PQM-700 Power Quality Analyzer

Product Information

Analysis
Software, Design and Measurement Methods, Calculation Formulas,
Power Quality – a Guide, Technical Specifications, Optional
Accessories
Safety Certifications| UL/cUL Safety Certification Mark – Investigated and certified
by Underwriters Laboratories (UL) in accordance with UL 61010-1,
3rd Edition, May 11, 2012, Revised July 15, 2015, IEC
61010-2-030:2010 (First Edition), UL 61010-2-030:2012 (First
Edition), CAN/CSA-C22.2 No. 61010-1-12, 3rd Edition, Revision dated
July 2015, CAN/CSA-C22.2 No. 61010-2-030-12 (First Edition)

Product Usage Instructions

Operation of the Analyzer

The PQM-700 Power Quality Analyzer provides functionality for
analyzing power quality parameters. Refer to the manual for
detailed instructions on operating the analyzer.

Sonel Analysis Software

The Sonel Analysis software is used in conjunction with the
PQM-700 Power Quality Analyzer. It provides additional analysis and
interpretation features for the collected data. Refer to the manual
for instructions on using the Sonel Analysis software.

Design and Measurement Methods

The analyzer supports voltage and current inputs for measuring
power quality parameters. The manual provides detailed information
on the design and measurement methods used by the analyzer.

Calculation Formulas

The manual includes calculation formulas for different types of
networks, such as one-phase network, split-phase network, 3-phase
wye network with N conductor, and 3-phase wye and delta network
without neutral conductor. These formulas can be used to perform
calculations related to power quality analysis.

Power Quality – a Guide

The manual contains a guide that provides basic information on
power quality and its importance. It also covers current
measurement techniques for power quality analysis.

Technical Specifications

The manual provides detailed technical specifications of the
PQM-700 Power Quality Analyzer, including information about inputs,
sampling and RTC (Real-Time Clock), and accuracy, resolution, and
ranges of measured parameters.

Optional Accessories

A list of optional accessories available for the PQM-700 Power
Quality Analyzer is provided in the manual. These accessories can
enhance the functionality and usability of the analyzer.

USER MANUAL POWER QUALITY ANALYZER
PQM-700
SONEL S.A. Wokulskiego 11 58-100 widnica
Poland
Version 1.15.8 30.06.2023

Due to continuous product development, the manufacturer reserves the right to make changes to functionality, features and technical parameters of the analyzers. This manual describes the firmware version 1.15 and the Sonel Analysis v4.4.8 software.

CONTENTS
1 General Information ……………………………………………………………………….. 6
1.1 Safety……………………………………………………………………………………………………6 1.2 General characteristics ……………………………………………………………………………7 1.3 Power supply of the analyzer ……………………………………………………………………9 1.4 Tightness and outdoor operation……………………………………………………………….9 1.5 Mounting on DIN rail ……………………………………………………………………………..10 1.6 Measured parameters ……………………………………………………………………………11 1.7 Compliance with standards …………………………………………………………………….13
2 Operation of the analyzer ……………………………………………………………… 14
2.1 Buttons ………………………………………………………………………………………………..14 2.2 Signalling LEDs…………………………………………………………………………………….14 2.3 Switching the analyzer ON/OFF………………………………………………………………14 2.4 Auto-off ……………………………………………………………………………………………….15 2.5 PC connection and data transmission ………………………………………………………15 2.6 Indication of connection error ………………………………………………………………….16 2.7 Warning about too high voltage or current ………………………………………………..17 2.8 Taking measurements……………………………………………………………………………17
2.8.1 Start / stop of recording…………………………………………………………………………………17 2.8.2 Approximate recording times …………………………………………………………………………17 2.9 Measuring arrangements ……………………………………………………………………….18 2.10 Inrush current ……………………………………………………………………………………….23 2.11 Key Lock ……………………………………………………………………………………………..23 2.12 Sleep mode ………………………………………………………………………………………….23 2.13 Firmware update …………………………………………………………………………………..24 2.13.1 Automatic update…………………………………………………………………………………………24 2.13.2 Manual update…………………………………………………………………………………………….24
3 “Sonel Analysis” software ……………………………………………………………. 25
4 Design and measurement methods ………………………………………………. 26
4.1 Voltage inputs ………………………………………………………………………………………26 4.2 Current inputs……………………………………………………………………………………….26
4.2.1 Digital integrator…………………………………………………………………………………………..26 4.3 Signal sampling…………………………………………………………………………………….27 4.4 PLL synchronization………………………………………………………………………………27 4.5 Frequency measurement ……………………………………………………………………….28 4.6 Harmonic components measuring method………………………………………………..28 4.7 Event detection …………………………………………………………………………………….29
5 Calculation formulas…………………………………………………………………….. 32
5.1 One-phase network……………………………………………………………………………….32 5.2 Split-phase network……………………………………………………………………………….35 5.3 3-phase wye network with N conductor…………………………………………………….37 5.4 3-phase wye and delta network without neutral conductor…………………………..40
3

5.5 Methods of parameter`s averaging…………………………………………………………..42
6 Power Quality – a guide ………………………………………………………………… 43
6.1 Basic Information ………………………………………………………………………………….43 6.2 Current measurement ……………………………………………………………………………44
6.2.1 Current transformer clamps (CT) for AC measurements …………………………………….44 6.2.2 AC/DC measurement clamps…………………………………………………………………………44 6.2.3 Flexible current probes …………………………………………………………………………………45 6.3 Flicker …………………………………………………………………………………………………45 6.4 Power measurement ……………………………………………………………………………..46 6.4.1 Active power ……………………………………………………………………………………………….47 6.4.2 Reactive power……………………………………………………………………………………………47 6.4.3 Reactive power and three-wire systems…………………………………………………………..50 6.4.4 Reactive power and reactive energy meters …………………………………………………….51 6.4.5 4-quadrant reactive energy measurement………………………………………………………..52 6.4.6 Apparent power …………………………………………………………………………………………..53 6.4.7 Distortion power DB and effective nonfundamental apparent power SeN ………………..55 6.4.8 Power factor ……………………………………………………………………………………………….55 6.5 Harmonics ……………………………………………………………………………………………56 6.5.1 Harmonics characteristics in three-phase system ……………………………………………..57 6.5.2 THD…………………………………………………………………………………………………………..58 6.5.3 TDD – Total Demand Distortion………………………………………………………………………59 6.6 Unbalance ……………………………………………………………………………………………60 6.7 Detection of voltage dip, swell and interruption ………………………………………….61 6.8 CBEMA and ANSI curves……………………………………………………………………….63 6.9 Averaging the measurement results…………………………………………………………64
7 Technical specifications ………………………………………………………………. 66
7.1 Inputs ………………………………………………………………………………………………….66 7.2 Sampling and RTC………………………………………………………………………………..67 7.3 Measured parameters – accuracy, resolution and ranges ……………………………67
7.3.1 Reference conditions ……………………………………………………………………………………67 7.3.2 Voltage ………………………………………………………………………………………………………68 7.3.3 Current ………………………………………………………………………………………………………68 7.3.4 Frequency ………………………………………………………………………………………………….69 7.3.5 Harmonics ………………………………………………………………………………………………….69 7.3.6 Power and energy………………………………………………………………………………………..69 7.3.7 Estimating the uncertainty of power and energy measurements…………………………..70 7.3.8 Flicker………………………………………………………………………………………………………..71 7.3.9 Unbalance ………………………………………………………………………………………………….72 7.4 Event detection – voltage and current RMS……………………………………………….72 7.5 Event detection – other parameters ………………………………………………………….72 7.5.1 Event detection hysteresis …………………………………………………………………………….73 7.6 Inrush current measurement …………………………………………………………………..73 7.7 Recording…………………………………………………………………………………………….73 7.8 Power supply, battery and heater…………………………………………………………….74 7.9 Supported networks ………………………………………………………………………………75 7.10 Supported current probes ………………………………………………………………………75 7.11 Communication …………………………………………………………………………………….75 7.12 Environmental conditions and other technical data …………………………………….76 7.13 Safety and electromagnetic compatibility ………………………………………………….76 7.14 Standards…………………………………………………………………………………………….76
8 Optional accessories ……………………………………………………………………. 77
4

9 Other information …………………………………………………………………………. 78 9.1 Cleaning and maintenance……………………………………………………………………..78 9.2 Storage ……………………………………………………………………………………………….78 9.3 Dismantling and disposal ……………………………………………………………………….78 9.4 Manufacturer ………………………………………………………………………………………..78
5

1 General Information

1 General Information
The following international symbols are used on the analyzer and in this manual:

Warning; See explanation in
manual

Functional earth terminal

Direct voltage/ current

Double Insulation (Protection Class)

Do no dispose of this product as un-
sorted municipal waste

Recycling information

UL/cUL Safety Certification Mark

Alternating voltage/ current
Conforms to relevant European Union direc-
tives (Conformité Européenne)
Conforms to relevant Australian standards

The PQM-700 (US model) analyzer has been investigated and certified by Underwriters Laboratories (UL) in accordance with the following Standards: UL 61010-1, 3rd Edition, May 11, 2012, Revised July 15 2015, IEC 61010-2-030: 2010 (First Edition), UL 61010-2-030: 2012 (First Edition), CAN/CSA-C22.2 No. 61010-1-12, 3rd Edition, Revision dated July 2015, CAN/CSA-C22.2 No. 61010-2-030-12 (First Edition).

It is UL/cUL listed under the UL File: E490376.

1.1 Safety
Warning
To avoid electric shock or fire, you must observe the following guidelines:
Before you proceed to operate the analyzer, acquaint yourself thoroughly with the present manual and observe the safety regulations and specifications provided by the producer.
Any application that differs from those specified in the present manual may result in damage to the device and constitute a source of danger for the user.
Analyzers must be operated only by appropriately qualified personnel with relevant certificates authorizing the personnel to perform works on electric systems. Operating the analyzer by unauthorized personnel may result in damage to the device and constitute a source of danger for the user.
The device must not be used for networks and devices in areas with special conditions, e.g. fire-risk and explosive-risk areas.
Before starting the work, check the analyzer, wires, current probes and other accessories for any sign of mechanical damage. Pay special attention to the connectors.
It is unacceptable to operate the device when: it is damaged and completely or partially out of order, its cords and cables have damaged insulation, of the device and accessories mechanically damaged.
Do not power the analyzer from sources other than those listed in this manual. Do not connect inputs of the analyzer to voltages higher than the rated values.
6

PQM-700 User Manual Use accessories and probes with a suitable rating and measuring category for the test-
ed circuit. Do not exceed the rated parameters of the lowest measurement category (CAT) of the
used measurement set consisting of the analyzer, probes and accessories. The measurement category of the entire set is the same as of the component with the lowest measurement category. If possible, connect the analyzer to the de- energized circuits. Opening the device socket plugs results in the loss of its tightness, leading to a possible damage in adverse weather conditions. It may also expose the user to the risk of electric shock. Do not handle or move the device while holding it only by its cables. Do not unscrew the nuts from the cable glands, as they are permanently fixed. Unscrewing the nuts will void the guarantee. Repairs may be performed only by an authorized service point.
The analyzer is equipped with an internal Li-Ion battery, which has been tested by an independent laboratory and is quality-certified for compliance with the standard UN Manual of Tests and Criteria Part III Subsection 38.3 (ST/SG/AC.10/11/Rev.5). Therefore, the analyzer is approved for air, maritime and road transport.
1.2 General characteristics
Power Quality Analyzer PQM-700 (Fig. 1) is a high-tech device providing its users with a comprehensive features for measuring, analysing and recording parameters of 50/60 Hz power networks and power quality in accordance with the European Standard EN 50160. The analyzer is fully compliant with the requirements of IEC 61000-4-30, Class S.
The device is equipped with four cables terminated with banana plugs, marked as L1, L2, L3, N. The range of voltages measured by the four measurement channels is max. ±1150 V. This range may be extended by using external voltage transducers.
Fig. 1. Power Quality Analyser PQM-700. General view. 7

1 General Information Current measurements are carried out using four current inputs installed on short cables ter-
minated with clamp terminals. The terminals may be connected to the following clamp types: flexible claps (marked as F-1(A), F-2(A)(HD), F-3(A)(HD)) with nominal rating up to 3000 A (differing from others only by coil diameter); and CT clamps marked as C-4(A) (range up to 1000 A AC), C5A (up to 1000 A AC/DC), C-6(A) (up to 10 A AC) and C-7(A) (up to 100 A AC). The values of nominal measured currents may be changed by using additional transducers – for example, using a transducer of 1000:5 ratio, the user may select C-6(A) clamps to measure currents up to 1000 A.
The device has a built-in 2 GB microSD memory card. Data from the memory card may be read via USB slot or by an external reader.
Note microSD card may be removed only when the analyzer is turned off. Removing the card during the operation of the analyser may result in the loss of important data.
Fig. 2. The rear wall of PQM-700 analyzer. Recorded parameters are divided into groups that may be independently turned on/off for recording purposes and this solution facilitates the rational management of the space on the memory card. Parameters that are not recorded, leave more memory space for further measurements. PQM-700 has an internal power supply adapter operating in a wide input voltage range (100…415 V AC / 140…415 V DC), which is provided with independent cables terminated with banana plugs. An important feature of the device is its ability to operate in harsh weather conditions ­ the analyzer may be installed directly on electric poles. The ingress protection class of the analyzer is IP65, and operating temperature ranges from -20°C to +55°C. 8

PQM-700 User Manual Uninterrupted operation of the device (in case of power failure) is ensured by an internal rechargeable lithium-ion battery. The user interface consists of five LEDs and 2 buttons. The full potential of the device may be released by using dedicated PC software Sonel Analysis. Communication with a PC is possible via USB connection, which provides the transmission speed up to 921.6 kbit/s
1.3 Power supply of the analyzer
The analyzer has a built-in power adapter with nominal voltage range of 100…415 V AC / 140…415 V DC (90…460 V AC / 127…460 V DC including fluctuations). The power adapter has independent terminals (red cables) marked with letter P (power) To prevent the power adapter from being damaged by undervoltage, it automatically switches off when powered with input voltages below approx. 80 V AC (110 V DC).
To maintain power supply to the device during power outages, the internal rechargeable battery is used. It is charged when the voltage is present at terminals of the AC adapter. The battery is able to maintain power supply up to 6 hours at temperatures of -20 °C…+55 °C. After the battery is discharged the meter stops its current operations (e.g. recording) and switches off in the emergency mode. When the power supply from mains returns, the analyzer resumes interrupted recording.
Note The battery may be replaced only by the manufacturer’s service de-
partment.
1.4 Tightness and outdoor operation
PQM-700 analyzer is designed to work in difficult weather conditions ­ it can be installed directly on electric poles. Two bands with buckles and two plastic fasteners are used for mounting the analyzer. The fasteners are screwed to the back wall of the housing, and bands should be passed through the resulting gaps.
Fig. 3. Fasteners for bands (for mounting the analyzer on a pole) 9

1 General Information The ingress protection class of the analyzer is IP65, and operating temperature ranges
from -20°C to +55°C. Note
In order to ensure the declared ingress protection class IP65, the following rules must be observed: Tightly insert the stoppers in the slots of USB and microSD card, Unused clamp terminals must be sealed with silicone stoppers.
At ambient temperatures below 0C or when the internal temperature drops below this point, the internal heater of the device is switched on ­ its task is to keep the internal temperature above zero, when ambient temperatures range from -20C to 0C.
The heater is powered from AC/DC adapter, and its power is limited to approx. 5 W. Due to the characteristics of the built-in lithium-ion rechargeable battery, the process of charging is blocked when the battery temperature is outside the range of 0C…60C (in such case, Sonel Analysis software indicates charging status as “charging suspended”).
1.5 Mounting on DIN rail
The device is supplied with a bracket for mounting the analyzer on a standard DIN rail. The bracket must be fixed to the back of the analyzer with the provided screws. The set includes also positioning catches (in addition to fasteners for mounting the analyzer on a pole), which should be installed to increase the stability of the mounting assembly. These catches have special hooks that are supported on the DIN rail.
Fig. 4. The rear wall of the analyzer with fixtures for mounting on DIN rail.
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PQM-700 User Manual
1.6 Measured parameters
PQM-700 analyzer is designed to measure and record the following parameters:
RMS phase and phase-to-phase voltages ­ up to 760 V (peak voltages ±1150 V), RMS currents:
up to 3000 A (peak currents ±10 kA) using flexible clamps (F-1(A), F-2(A)(HD), F-3(A)(HD)); up to 1000 A (peak values ±3600 A) using CT clamps (C-4(A) or C-5A); up to 10 A (peak values ±36 A) using C-6(A) clamps, up to 100 A (peak values ±360 A) using C-7(A) clamps, crest factors for current and voltage, mains frequency within the range of 40…70 Hz, active, reactive and apparent power and energy, distortion power, harmonics of voltages and currents (up to 40th), Total Harmonic Distortion THDF and THDR for current and voltage, power factor, cos, tan, unbalance factors for three-phase mains and symmetrical components, flicker PST and PLT , inrush current for up to 60 s.
Some of the parameters are aggregated (averaged) according to the time selected by the user and may be stored on a memory card. In addition to average value, it is also possible to record minimum and maximum values during the averaging period, and to record the current value occurring in the time of measurement.
The module for event detection is also expanded. According to EN 50160, typical events include voltage dip (reduction of RMS voltage to less than 90% of nominal voltage), swell (exceeding 110% of the nominal value) and interruption (reduction of the supplied voltage below 5% of the nominal voltage) The user does not have to enter the settings defined in EN 50160, as the software provides an automatic configuration of the device to obtain energy measurement mode compliant with EN 50160 The user may also perform manual configuration ­ the software is fully flexible in this area. Voltage is only one of many parameters for which the limits of event detection may be defined. For example, the analyzer may be configured to detect power factor drop below a defined value, THD exceeding another threshold, and the 9th voltage harmonic exceeding a userdefined percentage value. Each event is recorded along with the time of occurrence. For events that relate to exceeding the pre-defined limits for voltage dip, swell, interruption, and exceeding minimum and maximum current values, the recorded information may also include a waveform for voltage and current. It is possible to save two periods before the event, and four after the event.
A very wide range of configurations, including a multitude of measured parameters make PQM-700 analyzer an extremely useful and powerful tool for measuring and analysing all kinds of power supply systems and interferences occurring in them. Some of the unique features of this device make it distinguishable from other similar analyzers available in the market.
Tab. 1 presents a summary of parameters measured by PQM-700, depending on the mains type.
11

1 General Information

Tab. 1. Measured parameters for different network configurations.

Network type, channel
Parameter

U

RMS voltage

UDC

Voltage DC component

I

RMS current

IDC F CF U CF I P

Current DC component
Frequency
Voltage crest factor
Current crest factor
Active power

Q1, QB D, SN
S PF cos tanC-, tanL+ tanL-, tanC+ THD U
THD I
EP+, EPEQC-, EQL+ EQL-, EQC+
ES
Uh1..Uh40
Ih1..Ih40
Unbalance U, I

Reactive power
Distortion power
Apparent power
Power Factor
Displacement power factor
Tangent factor (4-quadrant)
Voltage Total harmonic dis-
tortion Current Total harmonic dis-
tortion Active energy
(consumed and supplied) Reactive energy (4-quadrant) Apparent en-
ergy Voltage harmonic ampli-
tudes Current harmonic ampli-
tudes Symmetrical components and unbalance
factors

Pst, Plt

Flicker factors

1phase L1/A N

2-phase L1/A L2/B N

3-phase wye with

3-phase triangle

N,

3-phase wye without N,

L1/A L2/B L3/C N L12/AB L23/BC L31/CA

(1)

(1)

(1)

Explanations: L1/A, L2/B, L3/C (L12/AB, L23/BC, L31/CA) indicate subsequent phases
N is a measurement for current channel IN ,
is the total value for the system. (1) In 3-wire networks, the total reactive power is calculated as inactive power = 2 – 2
(see discussion on reactive power in section 6.4)

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PQM-700 User Manual

1.7 Compliance with standards
PQM-700 is designed to meet the requirements of the following standards. Standards valid for measuring network parameters: IEC 61000-4-30:2009 ­ Electromagnetic compatibility (EMC) – Testing and measurement
techniques – Power quality measurement methods, IEC 61000-4-7:2002 ­ Electromagnetic compatibility (EMC) ­ Testing and Measurement Techniques – General Guide on Harmonics and Interharmonics Measurements and Instrumentation for Power Supply Systems and Equipment Connected to them, IEC 61000-4-15:2011 ­ Electromagnetic compatibility (EMC) ­ Testing and Measurement Techniques – Flickermeter ­ Functional and Design Specifications, EN 50160:2010 ­ Voltage characteristics of electricity supplied by public distribution networks.

Safety standards:
IEC 61010-1 ­ Safety requirements for electrical equipment for measurement control and laboratory use. Part 1: General requirements

Standards for electromagnetic compatibility:
IEC 61326 ­ Electrical equipment for measurement, control and laboratory use. Requirements for electromagnetic compatibility (EMC).

The device meets all the requirements of Class S as defined in IEC 61000-4-30. The summary of the requirements is presented in the table below.

Tab. 2. Summary of selected parameters in terms of their compliance with the standards

Aggregation of measurements at different intervals
Real-time clock (RTC) uncertainty
Frequency Power supply voltage Voltage fluctuations (flicker) Dips, interruptions and swells of supply voltage Supply voltage unbalance Voltage and current harmonics

IEC 61000-4-30 Class S: Basic measurement time for parameters (voltage, current, harmonics, unbal-
ance) is a 10-period interval for 50 Hz power supply system and 12-period interval for 60 Hz system, Interval of 3 s (150 periods for the nominal frequency of 50 Hz and 180 periods for 60 Hz), Interval of 10 minutes. IEC 61000-4-30 Class S: Built-in real-time clock, set via Sonel Analysis software, no GPS/radio synchronization. Clock accuracy better than ± 0.3 seconds/day Compliant with IEC 61000-4-30 Class S of the measurement method and uncertainty Compliant with IEC 61000-4-30 Class S of the measurement method and uncertainty The measurement method and uncertainty meets the requirements of IEC 61000-4-15 standard. Compliant with IEC 61000-4-30 Class S of the measurement method and uncertainty Compliant with IEC 61000-4-30 Class S of the measurement method and uncertainty Measurement method and uncertainty is in accordance with IEC 61000-4-7 Class I

13

2 Operation of the analyzer

2 Operation of the analyzer
2.1 Buttons

The keyboard of the analyzer consists of two buttons: ON/OFF

and START/STOP

. To switch-on the analyzer, press ON/OFF button. START/STOP button is used to start and stop recording.

2.2 Signalling LEDs

The analyzer is equipped with five LEDs that indicate different operating states:
ON (green) ­ the LED is on when the analyzer is turned on. During recording with activated sleep mode, the LED is off.
LOG (yellow) ­ indicates recording in process. In standby mode the LED is lit continuously. During recording it flashes. During recording with activated sleep mode ­ it is off and then switched on in 10-sec. intervals.
ERROR (red) ­ blinking of this LED indicates a potential problem with connecting to the tested network or the incompatibility of the active configuration with network parameters. Control criteria are defined in section 2.6. Continuous light indicates one of the possible internal errors of the analyzer (see also the description of additional statuses presented below).
MEM (red) ­ when this LED is on, it indicates that the data cannot be recorded on the memory card. MEM LED is continuously lit when the entire space on the memory card is filled. See also the description of additional statuses presented below.
BATT (red) – battery status. Blinking indicates that the battery is low (charged in 20% or less). When the battery is completely discharged, LED lights up for 5 seconds (with beep) and then the analyzer is switched off in emergency mode.

Additional statuses indicated by LEDs:
Continuous light of MEM and ERROR LEDs ­ no memory card, the card is damaged or not formatted. When these LEDs are on after inserting a memory card, there are two possible scenarios: o the card is damaged or incompatible with the analyzer. In this case there is no possi-

bility of further work with the analyzer. START button

is inactive.

o the card is not formatted (missing files required by the analyzer or files damaged) ­ in

this case you can press the START button

(it is active), which will start the pro-

cess of formatting the card (NOTE: all data on the card will be deleted). If the process

is successful MEM and ERROR LEDs will go off and the analyzer will be ready for fur-

ther work.

Blinking ON LED ­ FIRMWARE.PQF file detected on the card, containing the correct firm-

ware update file. You may press the START button

to begin the update process. Dur-

ing the update process ON and MEM LEDs blink simultaneously. After this process is com-

pleted, the meter will restart. You may skip the firmware update by pressing the ON/OFF but-

ton

or by waiting 10 seconds.

2.3 Switching the analyzer ON/OFF

The analyzer may be switched-on by pressing button

. Green ON LED indicates that

analyzer is switched on. Then, the analyzer performs a self-test and when an internal fault is

detected, ERROR LED is lit and a long beep (3 seconds) is emitted ­ measurements are

blocked. After the self-test, the meter begins to test if the connected mains configuration is the

same as the configuration in analyzer’s memory, and when an error is detected ERROR LED

flashes every 0.5 seconds. When ERROR LED flashes the analyzer still operates as normal

and measurements are possible.

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PQM-700 User Manual
When the meter is switched on and detects full memory, MEM LED is lit ­ measurements are blocked, only read-out mode for current data remains active.
When the meter is switched on and fails to detect the micro-SD card or detects its damage, ERROR and MEM LEDs are lit and measurements are blocked.

Note The ERROR and MEM LEDs behaves the same way when a new microSD card has been inserted to the analyzer’s slot. To format the card to be usable

with PQM-700 analyzer the

(START/STOP) button must be pressed.

Analyzer will then confirm start of formatting process with 3 beeps. All the da-

ta on the card will be erased. If the formatting finishes successfully the

ERROR and MEM LEDs will switch off, and the analyzer will be ready for fur-

ther operation.

If the connection test was successful, after pressing mode, as programmed in the PC.

the meter enters the recording

To switch the analyzer OFF, keep button recording lock are active.

pressed for 2 seconds, when no button or

2.4 Auto-off

When the analyzer operates for at least 30 minutes powered by the battery (no power supply from mains) and it is not in the recording mode and PC connection is inactive, the device automatically turns-off to prevent discharging the battery.
The analyzer turns off automatically also when the battery is fully discharged. Such an emergency stop is preceded by activating BATT LED for 5 s and it is performed regardless of the current mode of the analyzer. In case of active recording, it will be interrupted. When the power supply returns, the recording process is resumed.

2.5 PC connection and data transmission

When the meter is switched-on, its USB port remains active.
In the read-out mode for current data, PC software refreshes data with a frequency higher than once every 1 second.
During the recording process, the meter may transmit data already saved in memory. Data may be read until the data transmission starts.
During the recording process the user may view mains parameters in PC: – instantaneous values of current, voltage, all power values, total values for three phases, – harmonics and THD, – unbalance, – phasor diagrams for voltages and currents, – current and voltage waveforms drawn in real-time.

When connected to a PC, button

is locked, but when the analyzer operates with key

lock mode (e.g. during recording),

button is also locked.

To connect to the analyzer, enter its PIN code. The default code is 000 (three zeros). The PIN

code may be changed using Sonel Analysis software.

When wrong PIN is entered three times in a row, data transmission is blocked for 10 minutes.

Only after this time, it will be possible to re-entry PIN.

When within 30 sec of connecting a PC to the device no data exchange occurs between the

analyzer and the computer, the analyzer exits data exchange mode and terminates the

connection.

15

2 Operation of the analyzer

Notes

Holding down buttons

and

for 5 seconds results in an

emergency setting of PIN code (000).

If you the keys are locked during the recording process, this lock has a

higher priority (first the user would have to unlock buttons to reset the

emergency PIN). This is described in section 2.11.

USB is an interface that is continuously active and there is no way to disable it. To connect the analyzer, connect USB cable to your PC (USB slot in the device is located on the left side and is secured with a sealing cap). Before connecting the device, install Sonel Analysis software with the drivers on the computer. Transmission speed is 921.6 kbit/s.
2.6 Indication of connection error
During operation, the analyzer continuously monitors the measured parameters for compliance with the current configuration. Basing on several criteria listed below, the analyzer controls the lighting of ERROR LED. If the analyzer does not detect any inconsistency, this LED remains off. When at least one of the criteria indicates a potential problem, ERROR LED starts to blink.
The criteria used by the analyzer for detecting a connection error are as follows: deviation of RMS voltage exceeding ±15% of nominal value, deviation of the phase angle of the voltage fundamental component exceeding ±30 of the theoretical value with resistive load and symmetrical mains (see note below) deviation of the phase angle of the current fundamental component exceeding ±55 of the theoretical value with resistive load and symmetrical mains (see note below) network frequency deviation exceeding ±10% of the nominal frequency, in 3-phase 3- and 4-wire systems the analyzer also calculates the sum of all the currents (instantaneous values) and checks if it totals to zero. This helps in determining if all current probes are connected correctly (i.e. arrows on current probes facing to the load). If the calculated current sum RMS value is higher then 0.3% of Inom it is treated as an error and blinking ERROR LED.

Note To detect a phase error, the fundamental component of the measured sequence must be at least equal to 5% of the nominal voltage, or 1% of the nominal current. If this condition is not fulfilled, the correctness of angles
is not verified.

16

PQM-700 User Manual
2.7 Warning about too high voltage or current
During its operation, the analyzer monitors continuously the value of voltages and currents connected to the measuring inputs. If the voltage of any active phase exceeds approx. 20% of the nominal voltage (> 120% UNOM) set in the measurement configuration, a two-tone continuous beep is activated. The same applies for currents ­ an alarm signal is activated if the measured current in any of the active channels exceeds 20% of nominal current (range of clamps;

120% INOM). In such a situation, check whether the voltage and current in the measured network is within voltage and current limits allowable for the analyzer or check if the analyzer configuration is correct and change it, if necessary.
2.8 Taking measurements

2.8.1 Start / stop of recording

Recording may be triggered in three ways:

immediate triggering – manually by pressing PC ­ LOG LED flashes,

button after configuring the meter from a

scheduled triggering – according to time set in the PC. The user must first press

button to enter recording stand-by mode; in this case pressing

button does not trigger

the recording process immediately (the meter waits for the first pre-set time and starts

automatically). In standby mode LOG LED is lit continuously, after triggering it flashes,

threshold triggering. The user must first press

button to enter recording stand-by

mode; in this case pressing

button does not trigger the recording process immediately

­ the normal recording starts automatically after exceeding any threshold set in the settings.

In standby mode LOG LED is lit continuously, after triggering it flashes.

Stopping the recording process:

Recording may be manually stopped by holding for one second button application.

or from the PC

Recording ends automatically as scheduled (if the end time is set), in other cases the user

stops the recording (using button

or the software).

Recording ends automatically when the memory card is full. After finishing the recording, when the meter is not in the sleep mode, LOG LED turns off and
the meter waits for next operator commands.

If the meter had LEDs turned-off during the recording process, then after finishing the recording no LED is lit; pressing any button activates ON LED.

2.8.2 Approximate recording times
The maximum recording time depends on many factors such as the size of the memory card, averaging time, the type of system, number of recorded parameters, waveforms recording, event detection, and event thresholds. A few selected configurations are given in Tab. 3. The last column presents approximate recording times for 2 GB memory card. The typical configurations shown in Tab. 3 assumes that IN current measurement is enabled.

17

2 Operation of the analyzer

Tab. 3. Approximate recording times for a few typical configurations.

Configuration mode/profile

Averaging time

System type (current
measurement on)

according to EN 50160
according to the “Voltages and currents” profile according to the “Power and harmonics” profile

10 min 1 s 1 s

3-phase wye 3-phase wye 3-phase wye

Events

(1000 events)

Event waveforms

Waveforms after averag-
ing period

Approximate recording time with
2GB allocated space

(1000 events)

60 years

270 days

23 days

according to the “Power and harmonics” profile

1 s

3-phase wye

(1000 events) (1000 events)

22.5 day

all possible parameters
all possible parameters
all possible parameters
all possible parameters

10 min 10 s 10 s
10 s

3-phase wye

3-phase wye

1-phase 1-phase

(1000 events (1000 events

/ day)

/ day)

4 years 25 days 64 days
22 days

2.9 Measuring arrangements
The analyzer may be connected directly and indirectly to the following types of networks: 1-phase (Fig. 5), 2-phase (split-phase) with split-winding of the transformer (Fig. 6), 3-phase wye with a neutral conductor (Fig. 7), 3-phase wye without neutral conductor (Fig. 8), 3-phase delta (Fig. 9).
In three-wire systems, current may be measured by the Aron method, which uses only two clamps that measure linear currents IL1 and IL3. IL2 jest current is then calculated using the following formula:
2 = -1 – 3
This method can be used in delta systems (Fig. 10) and wye systems without a neutral conductor (Fig. 11).

Note As the voltage measuring channels in the analyzer are referenced to N input, then in systems where the neutral is not present, it is necessary to connect N input to L3 network terminal. In such systems, it is not required to connect L3 input of the analyzer to the tested network. It is shown in Fig. 8, Fig. 9, Fig. 10 and Fig. 11 (three-wire systems of wye and delta
type).

18

PQM-700 User Manual In systems with neutral conductor, the user may additionally activate current measurement in this conductor, after installing additional clamps in IN channel. This measurement is performed after activating in settings the option of Current in N conductor.
Note In order to correctly calculate total apparent power Se and total Power Factor (PF) in a 4-wire 3-phase system, it is necessary to measure the current in the neutral conductor. Then it is necessary to activate option Current in N conductor and to install
4 clamps as shown in Fig. 7. More information may be found in sec. 6.4.5.
Pay attention to the direction of current clamps (flexible and CT). The clamps should be installed with the arrow indicating the load direction. It may be verified by checking an active power measurement – in most types of passive receivers active power is positive. When clamps are incorrectly connected, it is possible to change their polarity using Sonel Analysis software.
The following figures show schematically how to connect the analyzer to the tested network depending on its type.
Fig. 5. Wiring diagram ­ single phase.
Fig. 6. Wiring diagram ­ 2-phase. 19

2 Operation of the analyzer Fig. 7. Wiring diagram ­ 3-phase wye with a neutral conductor. Fig. 8. Wiring diagram ­ 3-phase wye without neutral conductor.
20

PQM-700 User Manual Fig. 9. Wiring diagram ­ 3-phase delta. Fig. 10. Wiring diagram ­ 3-phase delta (current measurement using Aron method).
21

2 Operation of the analyzer
Fig. 11. Wiring diagram ­ 3-phase wye without neutral conductor (current measurement using Aron method).
Fig. 12. Wiring diagram ­ indirect system with transducers ­ wye configuration. 22

PQM-700 User Manual

Fig. 13. Wiring diagram ­ indirect system with transducers ­ delta configuration.

2.10 Inrush current
This function allows user to record half-period values of voltage and current within 60 sec after starting the measurement. After this time, the measurements are automatically stopped. Before the measurement, set aggregation time at ½ period. Other settings and measurement arrangements are not limited.

2.11 Key Lock

Using the PC program, the user may select an option of locking the keypad after starting the process of recording. This solution is designed to protect the analyzer against unauthorized stopping of the recording process. To unlock the keys, follow these steps:

press three times in a row

button in steps of 0.5 s and 1 s,

then press

button within 0.5 s to 1 s,

When buttons are pressed, the user hears the sounds of inactive buttons ­ after completing the whole sequence the meter emits a double beep.
2.12 Sleep mode
PC software has the feature that can activate the sleep mode. In this mode, when the user starts recording, the meter turns off LEDs after 10 seconds. From this moment the following options are available:

immediate triggering ­ after LEDs are turned off, LOG LED blinks every 10 s signalling the recording process,
triggering by event ­ after LEDs are turned off, LOG LED blinks every 30 s in stand-by mode, and when the recording process starts LOG LED starts to blink every 10 s,
scheduled triggering ­ after LEDs are turned off, LOG LED blinks every 30 s in stand-by mode, and when the recording process starts LOG LED starts to blink every 10 s.
23

2 Operation of the analyzer

In addition to the above cases:

if the user interrupts the recording process by pressing

, then LEDs are lit, unless the

next recording is triggered,

if the analyzer finishes the recording process due to the lack of space on the memory card or

due to a completed schedule, the LEDs remain off.

Pressing any button (shortly) activates ON LED (and possibly other LEDs e.g. MEM depending on the state) and activates desired feature (if available).

2.13 Firmware update
Firmware of the analyzer must be regularly updated in order to correct discovered errors or introduce new functionalities. When the firmware is updated, check whether a new version of Sonel Analysis (and vice versa) is available, if yes ­ proceed with the upgrade.

2.13.1 Automatic update
Automatic update (recommended) is carried out with Sonel Analysis software. If the user activates option Check online updates in the software settings, the software will connect to the update server during startup. If updates are available, they are displayed (with a list of changes) and the user can confirm their download. The check for updates may be also activated manually by entering the menu and selecting Help On-line update. If the firmware update is available and has been downloaded, you can upgrade the firmware of the meter. To do this:
1. Before starting the update, download all the data from the analyzer to a computer (download and save the recorded data on the disk).
2. Connect the analyzer to the mains for battery charging. 3. Connect the analyzer to the computer via a USB cable and establish a connection between
the analyzer and the application. Immediately after connecting, Sonel Analysis should display a message about the option of updating the firmware (if the user sets in software options “Check firmware version while connecting”). 4. After confirming the update, wait until the process is completed. 5. NOTE: After a successful update, it is necessary to program the analyzer at least once before starting recording, in order to avoid inconsistencies in the recorded data.

2.13.2 Manual update

Manual update requires saving the appropriate firmware file on the memory card and starting the update with the button.
1. Before starting the update, download all the data from the analyzer to a computer (download and save the recorded data on the disk).
2. Connect the analyzer to the mains for battery charging. 3. Download a new firmware from the manufacturer’s website www.sonel.pl. If the file is com-
pressed, extract file FIRMWARE.PQF. 4. FIRMWARE.PQF file must be saved in the root directory of the microSD card using an exter-
nal card reader. 5. Insert the card into the analyzer. ON LED indicates that the firmware file was recognized and
readiness to start the update.

6. Press START

button to begin the update. If the START button is not pressed within 10 sec-

onds, the update is cancelled. The process progress is indicated by blinking LEDs ON and MEM.

7. NOTE: After a successful update, it is necessary to program the analyzer at least once before

starting recording, in order to avoid inconsistencies in the recorded data.

24

PQM-700 User Manual
3 “Sonel Analysis” software
Sonel Analysis is an application required to work with PQM-700 analyzer. It enables the user to: configure the analyzer, read data from the device, real- time preview of the mains, delete data in the analyzer, present data in the tabular form, present data in the form of graphs, analysing data for compliance with EN 50160 standard (reports), or other user-defined refer-
ence conditions, independent operation of multiple devices, upgrade the software and the device firmware to newer versions.
Detailed manual for Sonel Analysis is available in a separate document (also downloadable from the manufacturer’s website www.sonel.pl).
25

4 Design and measurement methods
4 Design and measurement methods
4.1 Voltage inputs
The voltage input block is shown in Fig. 14. Three phase inputs L1/A, L2/B, L3/C have common reference line, which is the N (neutral) input. Such inputs configuration allows reducing the number of conductors necessary to connect the analyzer to the measured mains. Fig. 14 presents that the power supply circuit of the analyzer is independent of the measuring circuit. The power adapter has a nominal input voltage range 100…415 V AC (140…415 V DC) and has a separate terminals.
The analyzer has one voltage range, with voltage range ±1150V.

4.2 Current inputs
The analyzer has four independent current inputs with identical parameters. Current transformer (CT) clamps with voltage output in a 1 V standard, or several types of flexible (Rogowski) probes can be connected to each input.
A typical situation is using flexible clamps with built-in electronic integrator. However, the PQM-700 allows connecting the Rogowski coil alone to the input and a digital signal integration.

Fig. 14. Voltage Inputs and integrated AC power
adapter.

4.2.1 Digital integrator
The PQM-700 uses the solution with digital integration of signal coming directly from the Rogowski coil. Such approach has allowed the elimination of the analog integrator problems connected with the necessity to ensure declared long-term accuracy in difficult measuring environments. The analog integrators must also include the systems protecting the inputs from saturation in case DC voltage is present on the input.
A perfect integrator has an infinite amplification for DC signals which falls with the rate of 20 dB/decade of frequency. The phase shift is fixed over the whole frequency range and equals -90°.
Theoretically infinite amplification for a DC signal, if present on the integrator input, causes the input saturation near the power supply voltage and makes further operation impossible. In practically implemented systems, a solution is applied which limits the amplification for DC to a specified value, and in addition periodically zeroes the output. There are also techniques of active cancellation of DC voltage which involve its measurement and re-applying to the input, but with an opposite sign, which effectively cancels such voltage. There is a term “leaky integrator” which describes an integrator with finite DC gain. An analog leaky integrator is just an integrator featuring a capacitor shunted with a high-value resistor. Such a system is then identical with a low-pass filter of a very low pass frequency.
Digital integrator implementation ensures excellent long-term parameters ­ the entire procedure is performed by means of calculations, and aging of components, drifts, etc. have been eliminated. However, just like in the analog version, also here we can find the saturation problem and without a suitable counteraction the digital integration may become useless. It should be remembered that both, input amplifiers and analog-to-digital converters, have a given finite and undesirable offset which must be removed prior to integration. The PQM-700 analyzer firmware includes a digital filter which is to remove totally the DC voltage component. The filtered signal is subjected to digital integration. The resultant phase response has excellent properties, and the phase shift for most critical frequencies 50 and 60 Hz is minimal.
Ensuring the least possible phase shift between the voltage and current components is very important for obtaining small power measurement errors. It can be proven that approximate power

26

PQM-700 User Manual
measurement error can be described with the following relationship1:
Power measurement error phase error (in radians) × tan() × 100 %
where tan() is the tangent of the angle between the fundamental voltage and current components. From the formula, it can be concluded that the measurement errors are increasing as the displacement power factor is decreasing; for example, at the phase error of only 0.1° and cos = 0.5, the error is 0.3%. Anyway, for the power measurements to be accurate, the phase coincidence of voltage and current circuits must be the highest possible.
4.3 Signal sampling
The signal is sampled simultaneously in all eight channels at the frequency synchronized with the frequency of power supply voltage in the reference channel. This frequency equals 10.24 kHz for the 50 Hz and 60 Hz mains systems.
Each period includes then about 205 samples for 50 Hz systems, and about 170 samples for 60 Hz systems. A 16-bit analog-to-digital converter has been used which ensures 64-fold oversampling.
3-decibel channels attenuation has been specified for frequency of about 12 kHz, and the amplitude error for the 2.4 kHz maximum usable frequency (i.e. the frequency of 40th harmonics in the 60 Hz system) is about 0.3 dB. The phase shift for this frequency is below 15°. Attenuation in the stop band is above 75 dB.
Please note that for correct measurements of phase shift between the voltage harmonics in relation to current harmonics and power of these harmonics, the important factor is not absolute phase shift in relation to the basic frequency, but the phase coincidence of voltage and current circuits. The highest phase difference error for f = 2.4 kHz is maximum 15°. Such error is decreasing with the decreasing frequency. Also an additional error caused by used clamps are transducers must be considered when estimating the measurement errors for harmonics power measurements.
4.4 PLL synchronization
The sampling frequency synchronization has been implemented by hardware. After passing through the input circuits, the voltage signal is sent to a band-pass filter which is to reduce the harmonics level and pass only the voltage fundamental component. Then, the signal is sent to the phase locked loop circuits as a reference signal. The PLL system generates the frequency which is a multiple of the reference frequency necessary for clocking of the analog- to-digital converter.
The necessity to use the phase locked loop system results directly from the requirements of the IEC 61000-4-7 standard which describes the methodology and admissible errors during the measurements of harmonic components. The standard requires that the measuring window, being the basis for a single measurement and evaluation of harmonics content, is equal to the duration of 10 periods in the 50 Hz mains systems and 12 periods in the 60 Hz systems. In both cases, it corresponds to about 200 ms. Because the mains frequency can be subject to periodical changes and fluctuations, the window duration might not equal exactly 200 ms and for the 51 Hz frequency will be about 196 ms.
The standard also recommends that before the Fourier transform (to separate the spectral components), the data are not subject to windowing operation. Absence of frequency synchronization and allowing the situation in which the FFT is performed on the samples from not the integer number of periods can lead to spectral leakage. This phenomenon causes that the spectral line of a harmonic blurs also to a few neighboring interharmonic spectral lines which may lead to loss of data about actual level and power of the tested spectral line. The use of Hann weighting window, which reduces the undesirable spectral leakage, has been permitted, but is limited to the situations when the PLL has lost synchronization.
The IEC 61000-4-7 defines also the required accuracy of the synchronization block: the time
1 “Current sensing for energy metering”, William Koon, Analog Devices, Inc.
27

4 Design and measurement methods
between the sampling pulse rising edge and (M+1)-th pulse (where M is the number of samples in the measuring window) should equal the duration of indicated number of periods in the measuring window (10 or 12) with maximum allowed error of ±0,03%. To explain it in simpler terms, let’s use the following example. For nominal frequencies the measuring window duration is exactly 200ms. If the first sampling pulse occurs exactly at time t = 0, the first sampling pulse of the next measuring window should occur at t = 200±0.06 ms. ±60 µs is allowed deviation of the sampling edge. The standard also defines the recommended minimum frequency range at which the abovementioned synchronization system accuracy should be maintained and specifies it as ±5% of rated frequency that is 47.5…52.5 Hz and 57…63 Hz for 50 Hz and 60 Hz mains, respectively.
The input voltage range for which the PLL system will work correctly is quite another matter. The 61000-4-7 standard does not give here any concrete indications or requirements. The PQM700 PLL circuit needs L1-N voltage above 10 V for proper operation.
4.5 Frequency measurement
The signal for measurement of 10-second frequency values is taken from the L1 voltage channel. It is the same signal which is used for synchronization of the PLL. The L1 signal is sent to the 2nd order band pass filter which passband has been set to 40…70 Hz. This filter is to reduce the level of harmonic components. Then, a square signal is formed from such filtered waveform. The signal periods number and their duration is counted during the 10-second measuring cycle. 10-second time intervals are determined by the real time clock (every full multiple of 10-second time). The frequency is calculated as a ratio of counted periods to their duration.
4.6 Harmonic components measuring method
The harmonics are measured according to the recommendations given in the IEC 61000-4-7 standard. The standard specifies the measuring method for individual harmonic components.
The whole process comprises a few stages: synchronous sampling (10/12 periods), Fast Fourier Transform (FFT), grouping.
Fast Fourier Transform is performed on the 10/12-period measuring window (about 200 ms). As a result of FFT, we receive a set of spectral lines from the 0 Hz frequency (DC) to the 40th harmonics (about 2.0 kHz for 50Hz or 2.4 kHz for 60 Hz). The distance between successive spectral lines depends directly on the determined length of measuring window and is about 5 Hz.
As the PQM-700 analyzer collects 2048 samples per measuring window (for 50 Hz and 60 Hz), this fulfills the requirement of Fast Fourier Transform that the number of samples subjected to transformation equals a power of 2.
A very important thing is to maintain a constant synchronization of sampling with the mains. FFT can be performed only on the data which include a multiple of the mains period. This condition must be met in order to minimize a so- called spectral leakage which leads to falsified information about actual spectral lines levels. The PQM-700 meets these requirements because the sampling frequency is stabilized by the phase locked loop (PLL).
Because the sampling frequency can fluctuate over time, the standard provides for grouping together with the harmonics main spectral lines also of the spectral lines in their direct vicinity. The reason is that the components energy can pass partially to neighboring interharmonic components. There are two grouping methods: harmonic group (includes the main spectral line and five or six neighboring interharmonic
components on each side), harmonic subgroup (includes the main spectral line and one neighboring line on each side).
28

PQM-700 User Manual
Fig. 15. Determination of harmonic subgroups (50 Hz system). The IEC 61000-4-30 standard recommends that the harmonic subgroup method is used in power quality analyzers.
Example In order to calculate the 3rd harmonic component in the 50 Hz system, use the 150 Hz main spectral line and neighboring 145 Hz and 155 Hz lines.
The resultant amplitude is calculated with the RMS method.
4.7 Event detection
The PQM-700 analyzer gives a lot of event detection options in the tested mains system. An event is the situation when the parameter value exceeds the user-defined threshold. The fact of event occurrence is recorded on the memory card as an entry which includes: parameter type, channel in which the event occurred, times of event beginning and end, user-defined threshold value, parameter extreme value measure during the event, parameter average value measure during the event.
Depending on the parameter type, you can set one, two or three thresholds which will be checked by the analyzer. The table below lists all parameters for which the events can be detected, including specification of threshold types.
29

4 Design and measurement methods

Tab. 4. Event threshold types for individual parameters

Parameter

Interruption Dip Swell Minimum Maximum

U

RMS voltage

UDC

DC voltage

f

Frequency

CF U

Voltage crest factor

u2

Voltage negative sequence unbalance

Pst

Short-term flicker Pst

Plt

Long-term flicker Plt

I

RMS current

CF I

Current crest factor

i2

Current negative sequence unbalance

P

Active power

Q1, QB

Reactive power

S

Apparent power

D, SN

Distortion power

PF

Power factor

cos

Displacement power factor

tan

tan

EP+, EP- Active energy (consumed and supplied)

EQ+, EQ- Reactive energy (consumed and supplied)

ES

Apparent energy

THDF U

Voltage THDF

Uh2..Uh40

Voltage harmonic amplitudes (order n = 2…40)

THDF I

Current THDF

Ih2..Ih40

Current harmonic amplitudes (order n = 2…40)

Some parameters can take positive and negative values. Examples are active power, reactive power, power factor and DC voltage. As the event detection threshold can only be positive, in order to ensure correct detection for above-mentioned parameters, the analyzer compares with the threshold their absolute values.

Example Event threshold for active power has been set at 10 kW. If the load has a generator character, the active power with correct connection of clamps will be a negative value. If the measured absolute value exceeds the threshold, i.e. 10 kW (for example -11 kW) an event will be recorded ­ exceeding of the maximum active power.

Two parameter types: RMS voltage and RMS current can generate events for which the user can also have the waveforms record.
The analyzer records the waveforms of active channels (voltage and current) at the event start and end. In both cases, six periods are recorded: two before the start (end) of the event and four after start (end) of the event. The waveforms are recorded in an 8-bit format with 10.24 kHz sampling frequency.
The event information is recorded at its end. In some cases it may happen that event is active when the recording is stopped (i.e. the voltage dip continues). Information about such event is also recorded, but with the following changes: no event end time,
30

PQM-700 User Manual extreme value is only for the period until the stop of recording, average value is not given, only the beginning waveform is available for RMS voltage or current related events.
In order to eliminate repeated event detection when the parameter value oscillates around the threshold value, the analyzer has a functionality of user-defined event detection hysteresis. It is defined in percent in the following manner: for RMS voltage events, it is the percent of the nominal voltage range (for example 2% of
230 V, that is 4.6 V), for RMS current events, it is the percent of the nominal current range (for example for C-4
clamps and absence of transducers, the 2% hysteresis equals 0.02×1000 A = 20 A), for remaining parameters, the hysteresis is specified as a percent of maximum threshold (for
example, if the maximum threshold for current crest factor has been set to 4.0, the hysteresis will be 0.02×4.0 = 0.08.
31

5 Calculation formulas
5 Calculation formulas
5.1 One-phase network

Name

Parameter Designation

Voltage (True RMS)

UA

Voltage DC component

UADC

Frequency

F

Current (True RMS)

IA

Current constant component

IADC

Active power

P

Budeanu reactive power

QB

Reactive power of fundamental component

Q1

Apparent power

S

Apparent distortion power

SN

Budeanu distortion power

DB

Power Factor
Displacement power factor
32

PF
cos DPF

One-phase network

Unit V
V Hz A
A
W
var
var VA VA var –

Method of calculation

=

1

=1

2

where Ui is a subsequent sample of voltage UA-N

M = 2048 for 50 Hz and 60 Hz

=

1

=1

where Ui is a subsequent sample of voltage UA-N

M = 2048 for 50 Hz and 60 Hz

number of full voltage periods UA-N counted during 10-sec period (clock time) divided by the

total duration of full periods

=

1

=1

2

where Ii is subsequent sample of current IA

M = 2048 for 50 Hz and 60 Hz

=

1

=1

where Ii is a subsequent sample of current IA

M = 2048 for 50 Hz and 60 Hz

=

1

=1

where Ui is a subsequent sample of voltage UA-N

Ii is a subsequent sample of current IA

M = 2048 for 50 Hz and 60 Hz

40

= sin

=1
where Uh is h-th harmonic of voltage UA-N Ih jest h-th harmonic of current IA
h is h-th angle between harmonic Uh and Ih 1 = 11 sin 1
where U1 is fundamental component of voltage UA-N I1 is fundamental component of current IA
1 is angle between fundamental components U1 and I1

=

= 2 – (11)2

= 2 – 2 – 2

=

If PF < 0, then the load is of a generator type

If PF > 0, then the load is of a receiver type

cos = = cos(1 – 1)

tan(L+)

Tangent (4-quadrant)

tan(C-) tan(L-)

tan(C+)

Harmonic components of voltage and current
Total Harmonic Distortion for voltage, referred to the fundamental component
Total Harmonic Distortion for voltage, referred to RMS
Total Harmonic Distortion for current, referred to
the fundamental component
Total Harmonic Distortion for current, referred to RMS

Uhx Ihx THDUF
THDUR
THDIF
THDIR

TDD factor

TDD

Voltage crest factor

CFU

PQM-700 User Manual

where U1 is an absolute angle of the fundamental com-

ponent of voltage UA-N

I1 is an absolute angle of the fundamental component

of current IA

(+)

=

(+) +

–

where: EQ(L+) is the increase in reactive energy EQ(L+) (Budeanu/IEEE-1459) in a given averaging period,

EP+ is the increase in active power taken EP+ in a given

averaging period

(-)

=

–

(-) +

–

where: EQ(C-) is the increase in reactive energy EQC-)

(Budeanu/IEEE-1459) in a given averaging period,

EP+ is the increase in active power taken EP+ in a given

averaging period

(-)

=

(-) +

–

where: EQ(L-) is the increase in reactive energy EQ(L-) (Budeanu/IEEE-1459) in a given averaging period,

EP+ is the increase in active power taken EP+ in a given

averaging period

(+)

=

–

(+) +

–

where: EQ(C+) is the increase in reactive energy EQ(C+)

(Budeanu/IEEE-1459) in a given averaging period,

EP+ is the increase in active power taken EP+ in a given averaging period

V A

method of harmonic subgroups according to IEC 61000-4-7
x (harmonic) = 1..40

40=2 2

–

= 1 × 100%

where Uh is h-th harmonic of voltage UA-N

U1 is fundamental component of voltage UA-N

40=2 2

–

= × 100%

where Uh is h-th harmonic of voltage UA-N

40=2 2

–

= 1 × 100%

where Ih is h-th harmonic of current IA

I1 is fundamental component of current IA

40=2 2

–

= × 100%

where Ih is h-th harmonic of current IA

40=2 2 = × 100%

–

where Ih is the h-th harmonic of current IA

IL is demand current (in automatic mode IL it is the max-

imum average value of the fundamental component of

current, found in all measured current channels of the

entire recording range)

–

=

| |

||Where the operator expresses the highest abso-

33

5 Calculation formulas

Current crest factor

CFI

Short-term flicker

Pst

Long-term flicker

Plt

Active energy (consumed

EP+

and supplied)

EP-

Reactive energy (4-quadrant)

EQ(L+) EQ(C-) EQ(L-) EQ(C+)-

34

lute value of voltage UA-N samples

i = 2048 for 50 Hz and 60 Hz

–

||Where

the

=

||

operator expresses

the

highest

abso-

lute value of current IA samples

i = 2048 for 50 Hz and 60 Hz

–

calculated according to IEC 61000-4-15

Wh
varh

= 3=1 3

where PSTi is subsequent i-th indicator of short-term flicker

+ = +()() +() = {(0=)1(())>00

– = -()()

-()

=

{|(0=)1| ()()

< 0

0

where:

i is subsequent number of the 10/12-period measure-

ment window

P(i) represents active powerP calculated in i-th measur-

ing window

T(i) represents duration of i-th measuring window (in

hours)

(+) = +()()
=1
QL+(i) = Q(i) if Q(i)>0 i P(i)>0 QL+(i) = 0 in other cases

(-) = -()()
=1
QC-(i) = Q(i) if Q(i)>0 i P(i)<0 QC-(i) = 0 in other cases

(-) = -()()
=1
QL-(i) = |Q(i)| if Q(i)<0 i P(i)<0 QL-(i) = 0 in other cases

(+) = +()()
=1
QC+(i) = |Q(i)| if Q(i)<0 i P(i)>0 QC+(i) = 0 in other cases

where: i is subsequent number of the 10/12-period measurement window Q(i) represents active power (Budeanu or IEEE1459) calculated in i-th measuring window

PQM-700 User Manual
P(i) represents calculated active power in the i-th measuring window T(i) represents duration of i-th measuring window (in hours)

Apparent energy

= ()()

=1
where:

ES

VAh

i is subsequent number of the 10/12-period measurement window

S(i) represents apparent power S calculated in i-th

measuring window

T(i) represents duration of i-th measuring window (in

hours)

5.2 Split-phase network

Split-phase network
(parameters not mentioned are calculated as for single-phase)

Name

Parameter Designation

Total active power
Total Budeanu reactive power
Total reactive power of fundamental component
Total apparent power
Total apparent distortion power
Total Budeanu distortion power

Ptot QBtot Q1tot Stot SNtot DBtot

Total Power Factor
Total displacement power factor

PFtot
costot DPFtot

tantot(L+)

Total tangent (4-quadrant)

tantot(C-)

tantot(L-)

Unit W var var VA VA var –
–
–
–

Method of calculation

= +

= + 1 = 1 + 1
= + = +

= +

=

cos

=

=

1 2

(cos

cos )

(+)

=

(+) +

where: EQtot(L+) is the increase in total reactive energy

EQtot(L+) (Budeanu/IEEE-1459) in a given averaging peri-

od,

EPtot+ is the increase in total active energy EPtot+ in a

given averaging period

(-)

=

–

(-) +

where: EQtot(C-) is the increase in total reactive energy

EQtot(C-) (Budeanu/IEEE-1459) in a given averaging peri-

od,

EPtot+ is the increase in total active energy taken EPtot+

in a given averaging period

(-)

=

(-) +

where: EQtot(L-) is the increase in total reactive energy

35

5 Calculation formulas tantot(C+)

Total active energy (consumed and supplied)

EPtot+ EPtot-

Total reactive energy (4-quadrant)

EQtot(L+) EQtot(C-) EQtot(L-) EQtot(C+)

Wh
varh

EQtot(L-) (Budeanu/IEEE-1459) in a given averaging peri-

od,

EPtot+ is the increase in total active energy taken EPtot+

in a given averaging period

(+)

=

–

(+) +

where: EQtot(C+) is the increase in total reactive energy

EQtot(C+) (Budeanu/IEEE-1459) in a given averaging peri-

od,

EPtot+ is the increase in total active energy taken EPtot+

in a given averaging period

+ = +()()

+()

=

{0=(1)()()

0

0

– = -()()

=1
where:

i is subsequent number of the 10/12-period measure-

ment window,

Ptot(i) represents total active power Ptot calculated in i-th measuring window

T(i) represents duration of i-th measuring window (in

hours)

(+) = +()()
=1
QL+(i) = Q(i) if Q(i)>0 i P(i)>0 QL+(i) = 0 in other cases

(-) = -()()
=1
QC-(i) = Q(i) if Q(i)>0 i P(i)<0 QC-(i) = 0 in other cases

(-) = -()()
=1
QL-(i) = |Q(i)| if Q(i)<0 i P(i)<0 QL-(i) = 0 in other cases

(+) = +()()
=1
QC+(i) = |Q(i)| if Q(i)<0 i P(i)>0 QC+(i) = 0 in other cases
where: i is subsequent number of the 10/12-period measurement window, Q(i) represents total reactive power (Budeanu or IEEE1459) calculated in i-th measuring window, P(i) represents total active power calculated in i-th measuring window, T(i) represents duration of i-th measuring window (in hours)

36

Total apparent energy

EStot

PQM-700 User Manual

= ()()

=1
where:

VAh

i is subsequent number of the 10/12-period measurement window

Stot(i) represents total apparent power Stot calculated in i-

th measuring window

T(i) represents duration of i-th measuring window (in

hours)

5.3 3-phase wye network with N conductor

3-phase wye network with N conductor
(parameters not mentioned are calculated as for single-phase)

Name

Parameter Designation

Total active power

Ptot

Total Budeanu reactive power

QBtot

Total reactive power acc. to IEEE 1459

Q1+

Effective apparent power

Se

Unit W var var
VA

Method of calculation

= + + °

= + +

1+ = 31+1+ sin 1+
where: U1+ is the voltage positive sequence component (of the

fundamental component
I1+ his the current positive sequence component (of the
fundamental component) 1+ is the angle between components U1+ and I1+
= 3 where:

=

3(2

2

°2) + 18

2

2

2

Effective apparent distortion power

SeN

=

2

2

+ °2 3

2

= 2 + 12
where: 1 = 311

VA

1

=

3(12

1 2

12. • 12 18

12

12

Total Budeanu distortion power

DBtot

var

Total Power Factor

PFtot

–

Total displacement power factor

costot DPFtot

–

1

=

12

12

+ 3

12

12

= + +

=

cos

=

=

1 3

(cos

cos

cos°)

37

5 Calculation formulas

Total tangent (4-quadrant)
Total active energy (consumed and supplied)

tantot(L+) tantot(C-) tantot(L-) tantot(C+)
EP+tot EP-tot

Total reactive energy (4-quadrant)

EQtot(L+) EQtot(C-) EQtot(L-) EQtot(C+)

Total apparent energy

EStot

RMS value of zero voltage sequence

U0

RMS value of positive voltage sequence

U1

RMS value of negative voltage sequence

U2

Voltage unbalance factor for zero component

u0

Voltage unbalance factor for negative sequence

u2

–

calculated as for the split-phase network

Wh

formula same as in split-phase system

varh

calculated as for the split-phase network

= ()()

=1
where:

VAh

i is subsequent number of the 10/12-period measurement window

Se(i) represents the effective apparent power Se, calcu-

lated in i-th measuring window

T(i) represents duration of i-th measuring window (in

hours)

0

=

1 3

(1

1

1 )

V

0 = (0)

where UA1, UB1, UC1 are vectors of fundamental compo-

nents of phase voltages UA, UB, UC

Operator mag() indicates vector module

1

=

1 3

(1

1

2 1 )

1 = (1)

where UA1, UB1, UC1 are vectors of fundamental compo-

V

nents of phase voltages UA, UB, UC

Operator mag() indicates vector module

=

1120°

=

–

1 2

3 2

2 =

2

=

1 3

1240° (1 +

=

–

1 2

21

– +

3 2

2 = (2)

where UA1, UB1, UC1 are vectors of fundamental compo-

V

nents of phase voltages UA, UB, UC

Operator mag() indicates vector module

=

1120°

=

–

1 2

3 2

% %

2

=

1 0 2

==240°0121= 11-000012%%-

3 2

38

Current zero sequence

I0

RMS value of positive current sequence

I1

RMS value of negative current sequence

I2

Current unbalance factor for zero sequence

i0

Current unbalance factor for negative sequence

i2

PQM-700 User Manual

0

=

1 3

(1

1

A

0 = (0)
where IA1, IB1, IC1 are vectors of fundamental compo-

nents for phase currents IA, IB, IC

Operator mag() indicates vector module

1

=

1 3

(1

1

2 1)

A

1 = (1)
where IA1, IB1, IC1 are vectors of fundamental current

components IA, IB, IC

Operator mag() indicates vector module

2

=

1 3

(1

21

A

2 = (2)
where IA1, IB1, IC1 are vectors of fundamental compo-

nents for phase voltages IA, IB, IC

Operator mag() indicates vector module

% %

0 2

= =

0 12 1

100% 100%

39

5 Calculation formulas
5.4 3-phase wye and delta network without neutral conductor

3-phase wye and delta network without neutral conductor (Parameters: RMS voltage and current, DC components of voltage and current, THD, flicker are calculated as for 1-phase circuits; instead of the phase voltages, phase-to- phase voltages are used. Symmetrical components and unbalance factors are calculated
as in 3-phase 4-wire systems.)

Parameter

Name

Designation

Unit

Phase-to-phase voltage UCA

UCA

V

Current I2 (Aron measuring circuits)

I2

A

Method of calculation
= -( + ) 2 = -(1 + 3)

Total active power

Ptot

W

=

1

(
=1

=1

)

where:

UiAC is a subsequent sample of voltage UA-C

UiBC is a subsequent sample of voltage UB-C

IiA is a subsequent sample of current IA

IiB is a subsequent sample of current IB

M = 2048 for 50 Hz and 60 Hz

Total apparent power

Se

VA

= 3 where:

=

2

2 9

2

Total reactive power

(Budeanu and IEEE

Qtot

Total Budeanu distortion power

DBtot

Effective apparent distortion power

SeN

=

2

2 3

° 2

= = 2 – 2

var

where sign is equal to 1 or -1. The sign is determined

basing on the angle of phase shift between standardized

symmetrical components of voltages and currents

var

= 0

= 2 + 12
where: 1 = 311

VA

1

=

12

12 9

1 2

1

=

12

12 3

12

Total Power Factor

PFtot

–

Active energy (consumed and supplied)

EPtot+ EPtot-

Wh

40

=

+ = +()()
=1

Total apparent energy

EStot

PQM-700 User Manual

+ ()

=

{0()()()

0

0

– = -()()
=1

where:

-() = {|(0)|(()0) < 0

i is subsequent number of the 10/12-period measure-

ment window

Ptot(i) represents total active power Ptot calculated in i-th

measuring window

T(i) represents duration of i-th measuring window (in

hours)

= ()()

=1
where:

VAh

iis subsequent number of the 10/12-period measurement window

Se(i) represents the total apparent power Se calculated in

i-th measuring window

T(i) represents duration of i-th measuring window (in

hours)

41

5 Calculation formulas

5.5 Methods of parameter`s averaging
Method of averaging parameter

Parameter RMS Voltage DC voltage Frequency Crest factor U, I Symmetrical components U, I Unbalance factor U, I RMS Current Active, Reactive, Apparent and Distortion Power Power factor PF cos tan
THD U, I
Harmonic amplitudes U, I The angles between voltage and current harmonics Active and reactive power of harmonics

Averaging method RMS arithmetic average arithmetic average arithmetic average RMS calculated from average values of symmetrical components RMS arithmetic average
calculated from the averaged power values arithmetic average calculated as the ratio of the reactive energy delta (in the related quadrant) to the active energy delta calculated as the ratio of the average RMS value of the higher harmonics to the average RMS value of the fundamental component (for THD-F), or the ratio of the average of RMS value of higher harmonics to the average value of RMS value (for THD-R) RMS arithmetic average
arithmetic average

Note: RMS average value is calculated according to the formula:

=

1

,2
=1

The arithmetic average (AVG) is calculated according to the formula:

=

1

,
=1

where: Xi is subsequent parameter value to be averaged, N is the number of values to be averaged.

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PQM-700 User Manual
6 Power Quality – a guide
6.1 Basic Information
The measurement methodology is mostly imposed by the energy quality standards, mainly IEC 61000-4-30. This standard, introducing precise measurement algorithms, ordered analyzers market, allowing customers to easily compare the devices and their results between the analyzers from different manufacturers. Previously, these devices used different algorithms, and often the results from measurements on the same object were completely different when tested with different devices.
The factors behind growing interest in these issues have included wide use of electronic power controllers, DC/DC converters and switched-mode power supplies, energy-saving fluorescent lamps, etc., that is widely understood electrical power conversion. All of these devices had a tendency to significantly deform the supply current waveform. The design of switched-mode power supplies (widely used in household and industrial applications) is often based on the principle that the mains alternating voltage is first rectified and smoothed with the use of capacitors, meaning that it is converted to direct voltage (DC), and then with a high frequency and efficiency is converted to required output voltage. Such a solution, however, has an undesirable side effect. Smoothing capacitors are recharged by short current pulses at moments when the mains voltage is close to peak value. From power balance rule it is known that if the current is taken only at short intervals, its crest value must be much higher than in case it is taken in a continuous manner. High ratio of current crest value to RMS value (a socalled crest factor) and reduction of power factor (PF) will result in a situation in which in order to obtain a given active power in a receiver (in watts), the power supplier must supply power greater than the receiver active power (this is a so-called apparent power expressed in volt-amperes, VA). Low power factor causes higher load on the transmission cables and higher costs of electricity transfer. Harmonic current components accompanying such parameters cause additional problems. As a result, the electricity suppliers have started to impose financial penalties upon the customers who have not provided sufficiently high power factor.
Among entities that may be potentially interested in power quality analyzers are power utility companies on one hand, (they may use them to control their customers), and on the other hand the power consumers who may use the analyzers to detect and possibly improve the low power factor and solve other problems related to widely understood power quality issues.
The power source quality parameters, as well as the properties of receivers, are described with many various magnitudes and indicators. This section can shed some light on this area.
As already mentioned, the lack of standardization of measurement methods has caused significant differences in values of individual mains parameters calculated with various devices. Efforts of many engineers resulted in IEC 61000-4-30 standard concerning power quality. For the first time, this standard (and related standards) provided very precise methods, mathematical relations and required measurement accuracy for power quality analyzers. Compliance with the standard (in particular, the class A) should be a guarantee of repeatable and almost identical measurement results of the same magnitudes measured with devices from different manufacturers.
43

6 Power Quality – a guide
6.2 Current measurement

6.2.1 Current transformer clamps (CT) for AC measurements

CT Current Transformer is just a transformer converting a large current in primary winding to a

smaller current in secondary winding. The jaws of typical current clamp are made of a ferromag-

netic material (such as iron) with the secondary winding wound around. The primary winding is a

conductor around which the clamp jaws are closed, hence most

often it is one single coil. If the 1000-ampere current flows

through the tested conductor, in the secondary winding with

1000 coils the current will be only 1 A (if the circuit is closed). In

case of clamps with voltage output, a shunt resistor is located in

the clamps.

Such current transformer has a few characteristic properties.

It can be used to measure very large currents, and its power

consumption is low. The magnetizing current causes some

phase shift (tenth of a degree) which can result in some power

Fig. 16. Current

measurement error (particularly when the power factor is low).

transformer clamp with Another disadvantage of this clamp type is also the core satura-

voltage output.

tion phenomenon when very large currents are measured

(above the rated range). Core saturation as a result of magnetiz-

ing hysteresis leads to significant measurement errors which can

be eliminated only by the core demagnetization. The core becomes saturated also when the

measured current has a significant DC component. An undeniable disadvantage of such clamp is

also its considerable weight.

Despite such drawbacks, the CT clamps are presently the most widely used non- invasive al-

ternating current (AC) measurement method.

The following CT clamps can be used with the PQM-700 analyzers to measure alternating

currents:

C-4(A), rated range 1000 A AC,

C-6(A), rated range 10 A AC,

C-7(A), rated range 100 A AC.

6.2.2 AC/DC measurement clamps
There are situations when it is necessary to measure the current DC component. In such case, the clamps must be based on different principle of operation than a traditional current transformer. The clamps in this case use the physical phenomenon known as the Hall effect and include a Hall sensor. In brief: the effect is the production of voltage across an electrical conductor through which the current is flowing and which is placed in a magnetic field. The voltage is transverse to the field induction vector.
The clamps based on this phenomenon can measure the DC and AC current component. The conductor with current located inside the clamps generates a magnetic field which concentrates in an iron core. In the core slot, where both clamp parts are joined, placed is a semiconductor Hall sensor, and its output voltage is amplified by an electronic circuit supplied from a battery.
This clamp type usually has the current zero adjustment knob. To adjust the current zero, close the jaws (no conductor inside) and turn the knob until the DC indication is zero.
In the area of AC/DC measurement clamps, Sonel S.A. offers the C-5A clamp with rated range of 1000 A AC / 1400 A DC. This clamp has a voltage output and for 1000 A rated current it gives a 1 V voltage signal (1 mV/A).

44

PQM-700 User Manual

6.2.3 Flexible current probes

Flexible Current Probes are based on a totally dif-

ferent physical principle than the current transformer.

Their principal part is a so-called Rogowski coil, named

after German physicist Walter Rogowski. It is an air-

core coil wound around a conductor with current. Spe-

cial design of the coil allows leading out its both ends

on the same side, thus facilitating clamp placement

around the conductor (the return end is placed inside

the coil at its entire length). The current flowing through

the measured conductor causes centric magnetic field

lines which due to the self-induction phenomenon in-

duce the electromotive force at the end of the coil. This

voltage, however, is proportional to the rate of current

change in the conductor, and not to the current itself.

In comparison with current transformers, the

Rogowski coil has a few indisputable advantages. As it

does not have a core, the core saturation effect is elimi-

nated; thus being a perfect instrument to measure large

currents. Such coil has also an excellent linearity and a

wide pass band, much wider than a current transformer,

Fig. 17. Rogowski coil.

and its weight is much smaller.

However, until recently the wider expansion of flexi-

ble clamps in the current measurement area was diffi-

cult. There are some factors which hinder practical implementation of a measurement system with

a Rogowski coil. One of them is a very low voltage level which is induced on the clamps (it de-

pends on geometrical dimensions of the coil). For example, the output voltage for the 50 Hz fre-

quency of the F-series flexible probes (to be used with PQM-700) is about 45 µV/A. Such low

voltages require the use of precise and low-noise amplifiers which of course increase the costs.

Because the output voltage is proportional to the current derivative, it is necessary to use an

integrating circuit; generally, the flexible probes comprise a Rogowski coil and an analog integra-

tor circuit (characteristic battery-powered module). On the integrator output available is the volt-

age signal proportional to measured current and suitably scaled (for example 1 mV/A).

Another problem connected with the Rogowski coil is its sensitivity to external magnetic fields.

A perfect coil should be sensitive only to the fields closed within its area and should totally sup-

press external magnetic fields. But this is a very difficult task. The only way to obtain such proper-

ties is very precise manufacture of the coil, with perfectly homogenous windings and impedance

as low as possible. It is the high precision which causes a relatively high price of such probe.

The user may connect the analyzer to the flexible probes offered by Sonel S.A. Clamp types

and parameters are described in section 8.

6.3 Flicker

In terms of power quality, flicker means a periodical changes of the luminous intensity as a result of fluctuations of voltage supplied to light bulbs.
The flicker measurement function appeared in the power quality analyzers when it turned out that this phenomenon causes a deteriorated well-being, annoyance, sometimes headache, etc. The luminous intensity fluctuations must have a specified frequency, they may not be to slow as then human iris can adapt to changed lighting, and they may not be too fast because the filament inertia offsets these fluctuations almost totally.
The tests have proved that maximum arduousness occurs at the frequency of about 9 changes per second. The most sensitive light sources are traditional incandescent bulbs with tungsten filament. Halogen bulbs, which filaments have much higher temperature, have also much higher inertia which reduces the perceived brightness changes. Fluorescent lamps have the best flicker “resistance”, as due to their some specific properties they stabilize the current flowing through the lamp during the voltage changes, and thus reduce the fluctuations.

45

6 Power Quality – a guide
Flicker is measured in so-called perceptibility units, and there are two types of flicker: shortterm PST which is determined once every 10 minutes, and long- term PLT which is calculated on the basis of 12 consecutive PST values, i.e. every 2 hours. Long measurement time results directly from slow-changing character of this phenomenon ­ in order to collect a reliable data sample, the measurement must be long. PST equal to 1 is considered a value on the border of annoyance ­ certainly sensitivity to flicker is different in different people; this threshold has been adopted after tests carried out on a representative group of people.
What causes flicker? Most frequently, the reason is the voltage drop as a result of connecting and disconnecting large loads and some level of flicker is present in the majority of mains systems. Disregarding the unfavorable effect on humans described above, flicker does not need to be ­ and usually is not ­ a symptom of malfunctioning of our installation. However, if a rather abrupt and unexplainable flicker level increase is observed in the mains (increase of PST and PLT), this should not be ignored under any circumstances. It may turn out that the flicker is caused by unsure connections in the installation ­ increased voltage drops on connections in the distribution panel (for example) will result in higher voltage fluctuations on the receivers, such as light bulbs. The voltage drops on connections also cause their heating, and finally sparking and possibly a fire. Periodical mains tests and described symptoms can turn our attention and help find the source of hazard.
6.4 Power measurement
Power is one of the most important parameters defining the properties of electrical circuits. The basic magnitude used for financial settlements between the supplier and the consumer is electric energy which is the power multiplied by time. A few different power types can be found in electrical engineering: active power, designated as P and measured in watts, reactive power, designated as Q, unit is var, apparent power, S, unit is VA. These three types of power are the most known, but there are also other types.
At school we are taught that these three power types make up a so-called power triangle which properties are expressed by the following equation:
P2 + Q2 = S2
This equation is however correct only for systems with sinusoidal voltage and current waveforms.
Before a more detailed discussion about the power measurement, individual types of power should be defined.
46

PQM-700 User Manual

6.4.1 Active power
Active power P is a magnitude with precise physical meaning and it expresses the ability of a system to perform a given work. It is the power most desired by the energy consumers and it is for this supplied power that the consumer pays the supplier in a given settlement period (the problem of fees for additional reactive power is discussed separately ­ see below). It is the active power (and consequently, the active energy) which is measured by electric energy meters in each household.
Basic formula to calculate the active power is as follows:

=

1

()()

where: u(t) ­ instantaneous voltage value, i(t) – instantaneous current value, T ­ period for which the power is calculated.

In sinusoidal systems, the active power can be calculated as: =

where: U is RMS voltage, I is RMS current, and is the phase shift angle between the voltage and the current.
The PQM-700 analyzer calculates the active power directly from the integral formula, using sampled voltage and current waveforms:

=

1

=1

where M is a number of samples in the 10/12-period measuring window (2048 for the 50 Hz and 60 Hz system), Ui and Ii are successive voltage and current samples.

6.4.2 Reactive power
The most popular formula for reactive power is also correct only for one-phase circuits with sinusoidal voltage and current waveforms:

Interpretation of this power in such systems is as follows: it is an amplitude of AC component of instantaneous power on the source terminals. Existence of a non-zero value of this power indicates a bidirectional and oscillating energy flow between the source and the receiver.
Let us imagine a one-phase system with sinusoidal voltage source which load is a RC circuit. As under such conditions, the elements’ behavior is linear, the source current waveform will be sinusoidal, but due to the properties of capacitor it will be shifted in relation to source voltage. In such a system, reactive power Q will be non-zero and can be interpreted as an amplitude of energy oscillation which alternately is collected in the capacitor and returned to the source. Capacitor active power equals zero.
However, it turns out the energy oscillation seems only an effect, and that it appears in particular cases of circuits with sinusoidal current and voltage waveforms, and is not the cause of reactive power. Research in this area has shown that reactive power occurs also in circuits without any energy oscillation. This statement may surprise many engineers. In latest publications on power theory, the only physical phenomenon mentioned which always accompanies appearance of reactive power is phase shift between current and voltage.
The reactive power formula given above is correct only for one-phase sinusoidal circuits. The
47

6 Power Quality – a guide
question thus arises: how do we calculate the reactive power in non-sinusoidal systems? This question opens a proverbial Pandora’s box among electrical engineers. It turns out that the reactive power definition in real systems (and not only those idealized) has been subject to controversy and now (2009) we do not have one, generally accepted definition of reactive power in systems with non-sinusoidal voltage and current waveforms, not to mention even unbalanced three-phase systems. The IEEE (Institute of Electrical and Electronics Engineers) 1459-2000 standard (from 2000) does not give a formula for total reactive power for non-sinusoidal three-phase systems ­ as three basic types of power the standard mentions are active power, apparent power and ­ attention ­ nonactive power designated as N. Reactive power has been limited only to the fundamental component and designated Q1.
This standard is the last document of this type issued by recognized organization which was to put the power definition issues in order. It was even more necessary as the voices had been appearing in scientific circles for many years that the power definitions used so far may give erroneous results. Most of all, the controversies related to the definition of reactive and apparent power (and also distortion power ­ see below) in one- and three-phase systems with non-sinusoidal current and voltage waveforms.
In 1987, professor L.S. Czarnecki proved that the widely used definition of reactive power by Budeanu was wrong. This definition is still taught in some technical schools and it was proposed by professor Budeanu in 1927. The formula is as follows:

= sin
=0
where Un and In are voltage and current harmonics of order n, and n are angles between these components.
As, after this magnitude has been introduced, the known power triangle equation was not met for circuits with non-sinusoidal waveforms, Budeanu introduced a new magnitude called the distortion power:

= 2 – (2 + 2)

Distortion power was to represent in the system the power appearing due to distorted voltage

and current waveforms.

For years, reactive power had been associated with energy oscillations between the source

and the load. The formula indicates that according to Budeanu’s definition, the reactive power is a

sum of reactive power of individual harmonics. Due to the sin factor, such components can be

positive or negative, depending on the angle between the harmonics of voltage and current.

Hence, a situation is possible when total reactive power QB will be zero at non-zero harmonic components. Observation that at non-zero components, total reactive power can ­ according to

this definition ­ be zero is a key to a deeper analysis which finally allowed proving that in some

situations QB can give quite surprising results. The research has questioned the general belief that

there is a relation between energy oscillations and Budeanu reactive power QB. One can give ex-

amples of circuits in which despite oscillating character of instantaneous power waveform, reac-

tive power according to Budeanu is zero. Over the years, the scientists have not been able to

connect any physical phenomenon to the reactive power according to this definition.

Such doubts about the correctness of this definition of course also cast shadow on the related

distortion power DB. The scientists have started to look for answers to the question whether the

distortion power DB really is the measure of distorted waveforms in non- sinusoidal circuits. The

distortion is a situation in which the voltage waveform cannot be “put” on the current waveform

with two operations: change of amplitude and shift in time. In other words, if the following condi-

tion is met:

() = ( – )

48

PQM-700 User Manual
the voltage is not distorted in relation to the current. In case of sinusoidal voltage and load which is any combination of RLC elements, this condition is always met (for sinusoidal waveforms, these elements maintain linearity). However, when the voltage is distorted, the RLC load does not ensure absence of current distortion in relation to voltage any more, and the load is no longer linear ­ it is necessary to meet some additional conditions (module and phase of load impedance changing with frequency).
And then, is really DB a measure of such distortion? Unfortunately, also in this case the Budeanu’s power theory fails. It has been proven that the distortion power can be equal to zero in a situation when voltage is distorted in relation to current waveform, and vice versa, the distortion power can be non-zero at total absence of distortion.
Practical aspect of this power theory which relates to improvement of power factor in systems with reactive power was to be the feature to take the most advantage of correct definitions of reactive power. The compensation attempts based on the Budeanu reactive power and related distortion power fell through. These magnitudes did not allow even a correct calculation of correction capacitance which gives the maximum power factor. Sometimes, such attempts ended even with additional deterioration of power factor.
How come, then, that the Budeanu’s power theory has become so popular? There may be several reasons. Firstly, engineers got accustomed to old definitions and the curricula in schools have not been changed for years. This factor is often underestimated, though as a form of justification it can be said that this theory had not been refuted for 60 years. Secondly, in the 1920s there were no measuring instruments which could give insight in individual voltage and current harmonic components and it was difficult to verify new theories. Thirdly, distorted voltage and current waveforms (i.e. with high harmonics contents) are a result of revolution in electrical power engineering which did not start before the second part of the last century. Thyristors, controlled rectifiers, converters, etc. began to be widely used. All these caused very large current distortion in the mains, and consequently increased harmonic distortion. Only then, were the deficiencies of the Budeanu’s theory felt. Finally, fourthly, the scientific circles related to power utilities were aware of the fact that industrial plants had invested a fortune in the measuring infrastructure (energy meters). Each change is this respect could bring about huge financial consequences.
However, slow changes became visible in the views of electrical engineers. With time, as nonlinear loads were more and more frequent and the waveforms more and more distorted, the limitations of used formulas could no longer be tolerated.
A very significant event was the 2000 publication by IEEE of the standard 1459 called “Definitions for the Measurement of Electric Power Quantities Under Sinusoidal, Non-Sinusoidal, Balanced, or Unbalanced Conditions”. For the first time, Budeanu’s definition of reactive power has been listed as not recommended which should not be used in new reactive power and energy meters. Many magnitudes have been also divided into the part related to the current and voltage fundamental component (first harmonics) and the part related to remaining higher harmonics. In most cases, it is recognized that the usable part of energy is transmitted by the 50/60Hz components, with much smaller (and often harmful) participation of higher harmonics.
The standard also introduced a new magnitude ­ nonactive power N which represents all nonactive components of power:
= 2 – 2
Reactive power is one of the components of nonactive power N. In one-phase systems with sinusoidal voltage and current waveforms, N equals Q; hence the nonactive power does not have any other components. In three-phase systems, this is true only for symmetrical sinusoidal systems with a balanced purely resistive load.
Other nonactive power components are related to concrete physical phenomena. According to the professor Czarnecki’s theory, which is one of the best in explaining the physical phenomena in three-phase systems, the power equation in such systems is as follows:
2 = 2 + 2 + 2 + 2
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6 Power Quality – a guide

Ds is the scattered power which appears in the system as a result of changing load conductance with frequency. Hence, presence of reactive elements in the system may cause the scattered power. In this equation, reactive power Q appears when there is a phase shift between the voltage and current harmonics.
Du means the unbalanced power which is a measure of unbalance of a three-phase receiver. This component explains the situation in which an unbalanced three- phase load of a purely resistive character results in the power factor less than one. Such load does not have the reactive power Q, and still the results from the power triangle S, P, Q are totally different (the Budeanu’s power theory with its distortion power could not explain this situation either ­ in a purely resistive load, the distortion power DB equals zero).
An attempt to connect the IEEE 1459-2000 standard with the Czarnecki’s power theory leads to the conclusion that nonactive power conceals at least three separate physical phenomena
which influence the reduced effectiveness of energy transmission from the source to the receiver, i.e. reduction of the power factor.

=

=

2

2 +

2

2

In the IEEE 1459-2000 standard, reactive power known as Q has been limited to the fundamental component, for both one-phase and three-phase systems:
1 = 11 sin 1
In three-phase systems, only the positive sequence component is taken into consideration:
1+ = 31+1+ sin 1+
Correct measurement of this power requires the same phase rotation sequence (i.e. phase L2 delayed by 120 in relation to L1, phase L3 delayed by 240 in relation to L1).
The term of positive sequence component will be discussed in more detail in the section devoted to unbalance.
The value of reactive power of the fundamental component is the main value which allows estimating the size of capacitor to improve the displacement power factor (DPF), that is the displacement of the voltage fundamental components in relation to the current fundamental component (i.e. compensator of the reactive power of the fundamental component).
6.4.3 Reactive power and three-wire systems
Correct reactive power measurement is impossible in unbalanced receivers connected according to the three-wire system (delta and wye systems without the N conductor). Such statement may come as a surprise for many people.
The receiver can be treated as a “black box” with only 3 terminals available. We cannot determine its internal structure. In order to calculate the reactive power, we need to know the phase shift angle between the voltage and the current at each leg of such receiver. Unfortunately, we do not know this angle. In the delta-type receiver we know the voltages on individual impedances, but we do not know the current; in such systems, the phase-to- phase voltages and line currents are measured. Each line current is a sum of two phase currents. In the wye without N-type receivers, we know the currents flowing through impedance, but we do not know the voltages (each phase-to- phase voltage is a sum of two phase-to-neutral voltages.
We need to take account of the fact that at given voltage values at terminals and currents flowing into such “black box”, there is an infinite number of variants of receiver internal structure which will give us identical measurement results of voltage and current values visible outside the black box.
Then, how is it possible that there are reactive power meters intended for measurements in
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PQM-700 User Manual
three-wire systems and the mains analyzers which allow the reactive power measurement under such circumstances?
In both cases, the manufacturers use the trick which involves an artificial creation of a reference point (virtual neutral terminal N). Such point can be created very easily by connecting to the terminals of our black box a wye- connected system of three resistors of the same value.
In no case should a measuring instrument mislead the user, and such approximation can be allowed only after a clear reservation that the indicated value is not a result of actual measurement, but only an approximated value.
6.4.4 Reactive power and reactive energy meters
Reactive energy meters are devices unknown to the household users who for settlements with energy suppliers use the meters of active energy expressed in Wh or kWh. Household users are in a comfortable situation ­ they pay only for usable energy and do not have to think what the power factor is in their installations.
In contrast to the first group, the industrial consumers are obliged in their contracts and sometimes under pain of financial penalties to keep the power factor at an appropriate level.
The EN 50160 standard gives some guidelines for the power quality requirements, and defines the quality parameters which should be met by energy supplier. Among these parameters are, among others, mains frequency, RMS voltage, total harmonic distortion (THD) and allowed levels of individual voltage harmonics. Besides EN 50160 requirements there is often an additional condition: the supplier does not need to comply with those requirements if an energy consumer does not ensure the tan factor below some threshold (agreed value which can be changed in the contract between the energy supplier and consumer, i.e. 0.4) and/or exceeds the agreed level of consumed active energy.
The tan is defined as a ratio of measured reactive energy to the active energy in a settlement period. Going back for a while to the power triangle in sinusoidal systems, we can see that the tangent of the phase shift angle between the voltage and the current is equal to the ratio of reactive power Q to active power P. Consequently, the requirement to maintain the tan below 0.4 means nothing else but only that maximum level of measured reactive energy may not exceed 0.4 of the measured active energy. Each consumption of reactive energy above this level is subject to additional fees.
Does the knowledge of tan calculated in this manner give both interested parties an actual view of energy transmission effectiveness? Have we not mentioned before that the reactive power is only one of the nonactive power components which influence the power factor reduction? Indeed, it seems that instead of tan we should use the power factor PF which takes into account also other issues.
Unfortunately, if the present regulations leave no choice, than the correct reactive power measurement seems a key matter. Now, a question should be asked whether the reactive energy meters ensure correct readings in the light of the controversies described above. And what do such widely used meters really measure?
One can attempt to look for answers to these questions is the standard on such meters IEC 62053-23. Unfortunately, to our disappointment, we will not find there any reference to measurements in non-sinusoidal conditions ­ the calculation formulas relate to sinusoidal conditions (we can read in the standard that due to “practical” reasons, non-sinusoidal waveforms have been excluded). The standard does not give any measurement criteria which would allow checking the meter properties at distorted voltage and current waveforms. As a surprise comes also the fact that the older standard IEC 61268 (already withdrawn) defined the test which involved checking the measurement accuracy at 10% of the third current harmonic.
The present situation leaves the choice of measuring method to the meters designers, which unfortunately leads to significant differences in reactive energy indications in the presence of high harmonic distortion level.
Older, electromechanical meters have characteristics similar to that of a low- pass filter ­ higher harmonics are attenuated in such meters and the reactive power measurement in the presence of harmonics is very close to the value of reactive power of the fundamental component.
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6 Power Quality – a guide
Electronic meters which are more and more popular can perform the measurement with various methods. For example, they can measure active and apparent power, and then calculate the reactive power from the power triangle (square root from the sum of both such powers squared). In reality, in the view of the IEEE 1459-2000 standard, they measure the nonactive power, not the reactive power. Another manufacturer may use the method with voltage waveform shift by 90, which gives a result close to the reactive power of the fundamental component.
The higher the harmonics content, the higher difference in readings, and of course, as a consequence, other fees for measured energy.
As it has been signaled before, the reactive power measurement in unbalanced three-wire systems with traditional meters is subject to an additional error caused by creation of a virtual zero inside the meter which has little to do with actual zero of the receiver.
On top of that, the manufacturers usually do not give any information about the applied measuring method.
One can only wait impatiently for the next version of the standard, which ­ let’s hope ­ will define the measuring and testing methods much more precisely, also for non-sinusoidal conditions.
6.4.5 4-quadrant reactive energy measurement In the power sector, in many situations the reactive energy is divided into four separate com-
ponents, each of which is counted separately. This division into so-called quadrants is based on the signs of active and reactive power as shown in Fig. 18.
Fig. 18. Four-quadrant division of power and energy flow. quadrant I (marked as “L+”): active power is positive (receiving of active energy), reactive
power is positive (receiving of reactive power). In such conditions, the nature of the load is inductive. quadrant I (marked as “C-“): active power is negative (delivering of active energy), reactive power is positive (receiving of reactive power). The nature of the load is capacitive. quadrant III (marked as “L-“): active power is negative (delivering of active energy), reactive power is also negative (delivering of reactive energy). In such conditions, the nature of the load is inductive. quadrant IV (marked as “C+”): active power is positive (receiving of active energy), reactive power is negative (delivering of reactive power). The nature of the load is capacitive.
Plus and minus signs in marking quadrants indicate the sign of active power.
Presented division allows the construction of reactive energy meters, which increase their state only when the energy flow takes place in a given quadrant. This also means that at a given moment, only one of the counters can increase its status. 52

PQM-700 User Manual

In typical case of supplying the energy to a receiver, the operation takes place in two quadrants: I (L+) and IV (C+). Moreover, in these two quadrants the tangents ratio is monitored for customers connected to MV and LV networks in some countries. The four-quadrant tan coefficients are determined on the basis of recorded appropriate energy intakes:

(+)

=

(+) +

(+)

=

(+) +

If the convention is used, assuming all energy meters have a positive sign, the calculated values of tangents are complemented with a character resulting from the character of active and reactive power in a given quadrant. Thus, the sign of tan(L+) is always positive, while in case of tan(C+) it is always negative.

The calculated values of tangents may be the basis to calculate any penalties for reactive power consumption above the contracted level. In case of quadrant I (L+), a typical limit value above which fees are charged is 0.4. Often, for quadrant IV (C+) any reactive power consumption is the basis for calculating fines. This also results in practical conclusion that the most profitable
(for consumer) is operation in the first quadrant (L+) in the range of tan(L+) between 0 and 0.4.

6.4.6 Apparent power

Apparent power S is expressed as the product of RMS voltage and RMS current:

=

As such, the apparent power does not have a physical interpretation; it is used during designing of transmission equipment. In terms of value, it is equal to maximum active power which can be supplied to a load at given RMS voltage and current. Thus, the apparent power defines the maximum capacity of the source to supply usable energy to the receiver.

The measure of effective use of supplied power by the receiver is the power factor, which is the ratio of active power to apparent power.
In sinusoidal systems:

=

=

=

In non-sinusoidal systems such simplification is however not allowed, and the power factor is calculated on the basis of actual ratio of active power and apparent power.

=

In one-phase systems, the apparent power is calculated as shown in the formula above and there are no surprises. However, it turns out that in three-phase systems calculation of this power is equally difficult as calculation of reactive power. Of course, this is related to actual systems with non- sinusoidal waveforms which additionally can be unbalanced.
The tests have shown that the formulas used so far can give erroneous results if the system is unbalanced. As apparent power is a conventional magnitude and does not have a physical interpretation, determination which of proposed apparent power definitions is correct could be difficult. Yet, the attempts have been made based on the observation that the apparent power is closely related to the transmission losses and the power factor. Knowing the transmission losses and the
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6 Power Quality – a guide
power factor, one can indirectly specify a correct definition of apparent power. The definitions which have been used so far include arithmetic apparent power and vector
apparent power. The test have shown however that neither the arithmetic definition nor the vector definition give correct value of the power factor. The only definition which did not fail in such a situation, was the definition proposed as early as in 1922 by German physicist F. Buchholz:
= 3
It is based on RMS current and voltage, and the power is called an effective apparent power (hence, the index “e” in designations in three-phase systems). Those effective voltage and current values are such theoretical values which represent voltage and current in an energetically equivalent three-phase balanced system. Consequently, the key issue is to determine the Ue and Ie.
The IEEE 1459 standard gives the following formulas. In three-wire systems:

=

2

2 3

2

In four-wire systems:

=

2

2 9

2

=

2

2

+ 3

2

2

=

3( 2

2

2. • 18

2

2

2

where Ia, Ib, Ic, are RMS currents for individual phases (line or phase), In is the RMS current in neutral conductor, Ua, Ub, Uc are RMS phase-to-neutral voltages, and Uab, Ubc, Uca are RMS phase-to-phase voltages.

Se calculated in this manner includes both the power losses in the neutral conductor (in fourwire systems) and the effect of unbalance.

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PQM-700 User Manual
6.4.7 Distortion power DB and effective nonfundamental apparent power SeN
During the discussion on reactive power, it was proved that the distortion power according to Budeanu cannot be used at large voltage and current distortions and three-phase systems unbalance (a paradox of distortion power which is not a measure of actual distortion). Despite this fact, however, this power is often used by energy quality specialists and manufacturers of systems for reactive power compensation.
It must be clearly said that this parameter has given relatively good results only in conditions of slight distortion of voltage and current waveforms.
The IEEE 1459-2000 standard lists this definition of power, however just like in case of Budeanu reactive power, it has a non-removable defect and it is recommended to discard it entirely. Instead of DB, another value has been proposed which is a much better characteristics of total distortion power in a system – nonfundamental apparent power SeN. The SeN power allows a quick estimation whether a load works in conditions of small or large harmonic distortion; it is also a basis for estimating the static values and active filters or compensators.

where:

= 2 – 21

1 = 311
Effective current and effective voltage of the fundamental component (Ief and Uef respectively) are calculated similarly to Ie and Ue, but instead of RMS phase-to-neutral or phase-to-phase voltages, the effective voltages of fundamental components are substituted:

= 2 – (11)2

where U1 and I1 are effective values of fundamental components of phase-to- neutral voltage and current.

6.4.8 Power factor
True Power Factor or Power Factor (TPF or PF) is the value which takes into account also the presence of higher harmonics. For sinusoidal systems, it is equal to Displacement Power Factor (DPF), popular cos.
Hence, DPF is a measure of phase shift between the fundamental voltage and current components:

=

1 1

=

1111 11

=

11

The general formula for True Power Factor is:

=

In case of a purely resistive load (in a one-phase system), the apparent power is equal to active power (in terms of value), and reactive power equals zero, so such load fully uses the energy potential of the source and the power factor is 1. Appearance of reactive component inevitably leads to reduction of energy transmission effectiveness ­ the active power is then less than apparent power, and the reactive power is increasing.
In three-phase systems, the power factor reduction is also influenced by receiver unbalance (see discussion on reactive power). In such systems, correct power factor value is obtained using the effective apparent power Se that is the value defined, among others, in the IEEE 1459-2000 standard.

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6 Power Quality – a guide
6.5 Harmonics
Decomposition of periodic signal into harmonic components is a very popular mathematical operation based on Fourier’s theorem which says that any periodic signal can be represented as a sum of sinusoidal components with frequencies equal to multiples of basic frequency of such signal. Time-domain signal can be subjected to Fast Fourier Transform (FFT) to receive amplitudes and phases of harmonic components in the frequency domain.
In a perfect situation, voltage is generated in a generator which at output gives a pure sinusoidal 50/60 Hz waveform (absence of any higher harmonics). If the receiver is a linear system, then also current in such situation is a pure sinusoidal waveform. In real systems, voltage and current waveforms can be distorted, hence in addition to the fundamental component there must be harmonics of higher orders.
Why is the presence of higher harmonics in the system not desirable? One of the reasons is the skin effect which involves pushing out the electrons from the center of conductor towards the surface as the current frequency is increasing. As a result, the higher the frequency, the smaller the effective conductor cross section which is available for the electrons, which means that the conductor resistance is increasing. Consequently, the higher the current harmonics, the higher effective cabling resistance for this harmonics, and this inevitably leads to more power losses and heating.
A classic example connected with this effect is related to neutral conductor in three-phase systems. In a system with little distortion, little unbalance and a balanced (or slightly unbalanced) receiver, the current in neutral conductor has the tendency of zeroing (it is much smaller that RMS phase currents). Such observation has tempted many designers to obtains savings by installing the cabling in such systems with neutral conductor of a smaller cross section than in phase conductors. And everything went well until the appearance of odd harmonic orders which are multiples of 3 (third, ninth, etc.). Suddenly, the neutral conductor began overheating and the measurement showed very high RMS current. Explanation of this phenomenon is however rather simple. In this example, the designer did not take into consideration two circumstances: in systems with distorted waveforms, the higher harmonics might not zero in the neutral conductor, and quite to the contrary, they may sum up, and secondly, the skin effect and high harmonic currents additionally contributed to the neutral conductor heating.
Let us try now to answer two basic questions: What is the cause of harmonic components in voltage? What is the cause of harmonic components in current?
Seemingly, these two questions are almost identical, but separation of current and voltage is extremely important to understand the essence of this issue.
The answer to the first question is as follows: harmonics in voltage are a result on a non-zero impedance of the distribution system, between the generator (assuming that it generates a pure sinusoid) and the receiver.
Harmonics in current, on the other hand, are a result of non-linear impedance of the receiver. Of course, it must be noted that a linear receiver to which distorted voltage is supplied will also have identically distorted current waveform.
For years, in the literature the following statement has been used “receiver generates harmonics”. It should be remembered that in such case, the receiver is not a physical source of energy (as suggested by the word “generates”). The only source of energy is the distribution system. If the receiver is a passive device, the energy sent from the receiver to the distribution system comes from the same distribution system. What we have here is a disadvantageous and useless bidirectional energy flow. As discussed earlier in the section on power factor, such phenomenon leads to unnecessary energy losses, and the current “generated” in the receiver causes an additional load on the distribution system.
Let us consider the following example. A typical non-linear receiver, such as widely used switched-mode power supplies (i.e. for computers) receives power from a perfect generator of sinusoidal voltage. For the time being, let us assume that the impedance of connections between the generator and the receiver is zero. The voltage measured on the receiver terminals will have
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PQM-700 User Manual
sinusoidal waveform (absence of higher harmonics) ­ this is imply the generator voltage. The receiver current waveform will however include harmonic components ­ a non-linear receiver often takes current only in specified moments of the total sinusoid period (for example, maximum current can take place at the voltage sinusoid peaks).
However, the receiver does not generate these current harmonics, it simply takes current in a variable or discontinuous way. The whole energy is supplied only by the generator.
In the next step, we can modify the circuit by introducing some impedance between the generator and the receiver. Such impedance represents the resistance of cabling, transformer winding, etc.
Measurements of voltage and current harmonics will give slightly different results. What will change? Small voltage harmonics will appear, and in addition current frequency spectrum will slightly change.
When analyzing the voltage waveform on the receiver, one could notice that original sinusoidal waveform was slightly distorted. If the receiver took current mainly at voltage peaks, it would have visibly flattened tops. Large current taken at such moments results in larger voltage drops on the system impedance. A part of the ideal sinusoidal voltage is now dropped on this impedance. A change in the current spectrum is a result of slightly different waveform of voltage supplied to the receiver.
The example described above and “flattened tops” of the sinusoid are very frequent in typical systems to which switched-mode power supplies are connected.

6.5.1 Harmonics characteristics in three-phase system
In three-phase systems, the harmonics of given orders have a particular feature which is shown in the table below:

Order

1 2

3

4

5

6

7

8

9

Frequency [Hz] 50 100 150 200 250 300 350 400 450

Sequence

+ ­

0

­

0

­

0

(+ positive,

­ negative,

0 zero)

The row “Sequence” refers to the symmetrical components method which allows the resolution of any 3 vectors to three sets of vectors: positive sequence, negative sequence and zero se-
quence (more in the part related to unbalance).
Let us use an example. Assuming that a three-phase motor is supplied from a balanced, 4wire mains (RMS phase-to-neutral voltage values are equal, and angles between the individual
fundamental components are 120 each). Sign “+” in the row specifying the sequence for the 1st harmonics means the normal direction
of the motor shaft rotation. The voltage harmonics, for which the sign is also “+” cause the torque corresponding with the direction of the fundamental component. The harmonics of the 2nd, 5th, 8th and 11th order are the opposite sequence harmonics, meaning that they generate the torque which counteracts normal motor direction of rotation, which can cause heating, unnecessary en-
ergy losses, and reduced efficiency. The last group are the zero sequence components, such as the 3rd, 6th and 9th, which do not generate torque but flowing through the motor winding cause ad-
ditional heating. Based on the data from the table, it is easy to note that the series +, ­, 0 is repeated for all
successive harmonic orders. The formula which links the sequence with order is very simple, and
for k being any integer:

Sequence “+” positive “­” negative
“0” zero

Harmonic order 3k +1 3k ­ 1 3k

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6 Power Quality – a guide
The even order harmonics do not appear when a given waveform is symmetrical in relation to its average value, and this is the case in majority of power supply systems. In a typical situation, the measured even order harmonics have minimum values. If we consider this property, it turns out that the group of harmonics with the most undesirable properties is the 3rd, 9th, 15th (zero sequence), and the 5th, 11th, and 17th (negative sequence).
The current harmonics which are multiples of 3 cause additional problems in some systems. In 4-wire systems, they have a very undesirable property of summing up in the neutral conductor. It turns out that, contrary to other order harmonics, in which the sum of instantaneous current values is zeroed, the waveforms of these harmonics are in phase with each other which causes adding of the phase currents in the neutral conductor. This can lead to overheating of such conductor (particularly in the distribution systems in which this conductor has a smaller cross section than the phase conductors, and this was widely practiced until recently). Therefore, in systems with non- linear loads and large current distortions, it is now recommended that the cross section of neutral conductor is larger than that of the phased conductors. In the delta systems, the harmonics of these orders are not present in the line currents (provided these are balanced systems), but they circulate in the load branches, also causing unnecessary power losses.
Character of individual harmonics as shown in the table is fully accurate only in three-phase balanced systems. Only in such systems, the fundamental component has the exclusively positive sequence character. In actual systems, with some degree of supply voltage unbalance and the load unbalance, there are non-zero positive and negative sequence components. The measure of such unbalance is so-called unbalance factors. And this is due to this unbalance of the fundamental component and additionally the differences in amplitudes and phases of the higher harmonics, that also these harmonics will have the

References

• Sonel S.A.
• Sonel S.A.
• Sonel S.A.
• Sonel S.A.

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