Sonel PQM-700 Power Quality Analyzer User Manual
- June 14, 2024
- Sonel
Table of Contents
PQM-700 Power Quality Analyzer
Product Information
| Product Name | Power Quality Analyzer PQM-700 |
|---|---|
| Manufacturer | SONEL S.A. |
| Address | Wokulskiego 11, 58-100 widnica, Poland |
| Version | 1.15.8 (Firmware), 30.06.2023 (Software) |
| Manual Contents | General Information, Operation of the Analyzer, Sonel |
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.
10
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)
12
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.
14
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 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.
42
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:
() = ( – )
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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
-
- 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
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