ENSTO Low Voltage Overhead Line Equipment and Earthing Connectors Instruction Manual
- June 13, 2024
- ENSTO
Table of Contents
Low Voltage Overhead Line Equipment and Earthing Connectors
Product Information
The Installation Handbook provides recommended practices for
correct medium-voltage cable preparation and usage of underground
cable accessories. It is specifically aimed at installers and
includes information on cable accessories, tubing technology, and
cable construction. The handbook also highlights common errors in
installation and cable preparation to raise awareness among
installers.
The tools mentioned in the handbook are not the only suitable
ones for cable preparation, but they are recommended based on
Ensto’s experience and positive feedback from customers and
installers worldwide.
Table of Contents
- Medium-voltage cable accessories
- Heat-shrink technology
- Cold-shrink and hybrid technology
- Cable preparation
- Basic construction of an extruded cable
- Outer sheath and metallic screen
- Outer sheath removal
- Insulation screen
- Insulation screen removal
- Additional comments on the insulation screen
- Insulation
- Insulation removal
- Additional comments on the insulation
- Conductors
- Transition joints and paper-insulated cables
- Parts of a paper insulated cable
- Types of medium-voltage paper-insulated cables
- Preparation before the installation
- Installation errors
- Ensto Pro and Installer Certification
- Cable tools
Product Usage Instructions
Medium-voltage cable accessories: Cable
accessories are used to connect two cables together or one cable to
the terminal of another piece of equipment. They provide
insulation, galvanic connection, and control of the electric field.
Ensto manufactures heat-shrink, fully coldshrink, and hybrid
accessories for medium-voltage cables.
Cable joint: A cable joint is used to connect
two cables together. Straight joints are used when the insulation
material of both cables is the same. Transition joints are used to
connect a paper insulated cable to a polymeric insulated cable.
Screen break joints enable cross bonding the screens of the three
individual cable circuits.
Termination: A cable termination is used at the
end of the line to permanently connect a cable to the terminal of a
piece of equipment. Cable terminations are designed for indoor or
outdoor use and are resistant to UV radiation, environmental
elements, and dirt.
Screened separable connector: A screened
connector is used to terminate a cable with polymeric insulation
onto transformers, motors, or switchgears. These connectors are
touch-safe, require no maintenance, and can be used both indoors
and outdoors.
Heat-shrink technology: Heat-shrink accessories
provide mechanical robustness. These accessories require the use of
a flame to shrink the tubes and melt the glue and mastics
underneath. Ensto heat-shrink accessories include conductive,
insulating, and stress components.
Installation handbook
Cable preparation for medium-voltage underground cable accessories
Recommended practices for correct medium-voltage cable preparation. ensto.fi
This handbook is aimed at installers of medium-voltage underground cable
accessories, focused on cable preparation and correct usage concerning
recommended tools. Complementary information of cable accessories, tubing
technology and cable construction is also included.
Incorrect cable preparation is one of the main causes of failure in medium-
voltage cable accessories. Examples of common errors in installation and cable
preparation are also shown to raise awareness among installers.
The tools presented in this handbook are by no means the best or the only
suitable ones for cable preparation, but rather, the ones we recommend based
on our experience with internal use and the positive feedback received from
customers and installers worldwide.
Table of Contents
Medium-voltage cable accessories
5
Heat-shrink technology
6
Cold-shrink and hybrid technology
7
Cable preparation
8
Basic construction of an extruded cable
9
Outer sheath and metallic screen
10
Outer sheath removal
11
Insulation screen
17
Insulation screen removal
18
Additional comments on the insulation screen 20
Insulation
21
Insulation removal
22
Additional comments on the insulation
25
Conductors
26
Transition joints and paper-insulated cables
29
Parts of a paper insulated cable
30
Types of medium-voltage paper-insulated cables 31
Preparation before the installation
35
Installation errors
36
Ensto Pro and Installer Certification
39
Cable tools
40
3
Installers play a key role in the reliability of underground distribution networks
Medium-voltage cable accessories
Cable accessories are used to connect two cables together or one cable to the
terminal of another piece of equipment. They provide enough insulation,
galvanic connection and control of the electric field. Ensto manufactures
heat-shrink, fully coldshrink and hybrid accessories for medium-voltage
cables.
Cable joint A cable joint is used to connect two cables together. Straight
joints are used when the insulation material of both cables is the same.
Transition joints are used to connect a paper insulated cable to a polymeric
insulated cable. Screen break joints enable cross bonding the screens of the
three individual cable circuits.
Termination A cable termination is used at the end of the line to permanently
connect a cable to the terminal of a piece of equipment. Given their exposure
to UV radiation, environmental elements and dirt, cable terminations are
designed for indoor or outdoor use.
Screened separable connector A screened connector is used to terminate a cable
with polymeric insulation onto transformers, motors or switchgears. These
connectors are touch-safe, free of maintenance and suitable for both indoor
and outdoor use.
5
Heat-shrink technology
The mechanical robustness of heat-shrink accessories is the main advantage of the technology.
Heat-shrink accessories require a flame to shrink the tubes and to melt the
glue and mastics underneath.
The typical heat-shrink components found in Ensto accessories are: >
Conductive, insulating and stress
control tubes. > Conductive and insulating cable break-
outs. > Rain sheds.
Ensto manufactures medium-voltage heat-shrink cable joints and terminations (for indoor and outdoor use) for polymeric insulated and paper insulated cables.
Stress control and sealing mastics are
sensitive to heat and melt when the tubes are heated
6
Cold-shrink and hybrid technology
The reliability of several components integrated into one body and shorter installation times are the main advantages of cold-shrink and hybrid technologies.
Cold-shrink accessories are the solution in places where hot work is not
possible or permits are difficult to obtain. A silicone body with integrated
components is molded and then pre-expanded on a spiral or tube, ready to be
installed without using any flame.
Hybrid accessories include silicone bodies with heat-shrink outer sealing
tubes, an alternative that combines the advantages of both cold and heatshrink
technologies.
Ensto manufactures medium-voltage cold-shrink and hybrid joints, terminations
(for indoor and outdoor use) and screened separable connectors.
Why silicone? > Great molding performance > Resistant to environmental stress,
such as UV radiation, heat, moisture, oil and ozone. > Inorganic material that
doesn’t absorb dirt and humidity, therefore insulation properties remain
excellent.
The cold-shrink components found in Ensto accessories are: > Silicone
termination body with inte-
grated geometric stress control cone. > Silicone joint body with integrated
conductive electrode and geometric stress control cones, painted with a
conductive outer layer (in hybrid joints) > Fully cold shrink silicone joint
body with integrated conductive electrode, geometric stress control cones,
grounding grater for screening and outer sheath for sealing and waterproofing.
7
Cable preparation
In most cases, faults that occur in cable accessories are the result of errors in cable preparation.
The cable preparation process is critical. The accessory emulates the
structure of the cable, layer by layer, and provides a safe and reliable
transition when jointing with another cable or terminating the cable at the
end of the line.
Polymeric insulated extruded cables Cables with extruded polymeric insulation
have a very consistent structure among different models and manufacturers. The
main differences from the installer perspective are the types of insulation
screen and the different methods and tools for correct handling.
Insulation material The insulation material most widely used in modern
underground polymeric insulated cables are cross-linked polyethylene (XLPE)
and ethylene propylene rubber (EPR).
At the core of an underground cable, the conductor screen, the insulation and
the insulation screen are co-extruded. Installers must carefully prepare the
insulation and the screen, because the electrical behavior is controlled by
these parts of the cable and their equivalent or corresponding part in the
accessory kit.
8
Basic construction of an extruded cable
1
2
3
4
5
1
3
5
Outer sheath Also known as outer jacket. The outermost layer of the cable that
provides protection from the environment.
Certain components for armoring, earthing and/or waterproofing are bonded to
the outer sheath or extruded underneath it. Installers select the correct set
of tools based also on what material the outer sheath is made of. When the
metallic screen is made of aluminum laminate, the use of flame is possible for
outer sheath removal, and is even recommended in some cases.
2
Metallic screen Also known as cable shield or cable screen. Provides an earth
connection and a path for fault and leakage currents.
Aluminum (laminate or wires) or copper (wires or tape) are used to screen
extruded medium-voltage cables.
Insulation screen Also known as the semi-conductive layer. Provides a
homogeneous distribution of the electric field around the external layer of
the insulation.
The insulation screen can be bonded or strippable by hand. It also provides a
smooth transition between the insulation and the metallic screen. From the
installer’s point of view, the removal of the insulation screen is the most
critical step during cable preparation.
4
Insulation The insulation thickness is defined by the rated voltage of the
cable.
To prevent short circuits, a polymeric insulation is extruded around the
conductor screen. The two most typical insulation materials used in medium-
voltage extruded cables are cross-linked polyethylene (XLPE) and ethylene
propene rubber (EPR).
Conductors The cross section defines how much current can flow through the
cable.
Built in copper (more conductive) or aluminum (less heavy). Conductors have
two types of construction, circular and sector-shaped. In both cases, compact
stranded (several wires) or one solid conductor can be found. Sector-shaped
construction is used to decrease the total diameter of the cable.
Around the conductors, an extruded screen provides a smooth transition between
conductive and insulating materials, not allowing dangerous concentrations of
electric field in the surface of the conductors. The conductor screen is
removed along with the insulation.
9
Outer sheath and metallic screen
The metallic screen defines what tool can be used for removing the outer
sheath.
Always clean the outer sheath
before removal
The outer sheath provides protection to the cable. It insulates the metallic
screen from the ground and protects from corrosion and humidity.
The metallic screen keeps the field contained within the cable, contributes to
waterproofing (in the case of aluminum laminate) and allows partial
circulation of short-circuit currents.
Also, relevant information about the cable is marked or printed on the outer
sheath, i.e., cable type, nominal voltage, cross section, manufacturer, phase
marking, etc.
Function of the outer sheath > Insulation and corrosion protection
for the metallic screen > Reduction of the contribution of cables
to fire propagation > Mechanical protection > Information about the cable
Materials and features The outer sheath must be fire retardant and protect the
cable from the environment (animals and weather). PVC and PE are widely used
for their mechanical strength and fire retardant properties, but corrosive and
toxic fumes are released if the burning point is reached.
Halogen-free, fire-retardant materials are not as mechanically strong as PVC
or PE but reduce the spread of fire and fumes harmful to personnel and
equipment in case of fire.
The metallic screen is made of aluminum or copper. The two most typical
screens in extruded cables are aluminum laminate and copper wires. The
aluminum laminate is removed with the outer sheath and extended with a
grounding grater or braid. Copper wires are treated independently and
terminated or jointed by a lug or connector.
10
Outer sheath removal
Multifunction tool for outer sheath and insulation removal
Scan QR code for video demonstration or click here.
Multifunction tool Ensto ST281 > Removes outer sheath of single core
cables with aluminum laminate. > Removes all types of polymeric insu-
lation. > Teflon pads for minimum friction. > Stopper included. > Adjustable
blade depth. > Adjustable blade angle.
Instructions > Place the tool at the cut edge of the
cable. > Adjust the depth of the blade no
deeper than the aluminum laminate. > Adjust the angle of the blade to its
minimum. > Rotate the tool through the desired
length. > Adjust the angle of the blade to its
maximum when reaching the desired peeling length. > Perform the final round
cut.
Tips > To avoid damaging the insulation
screen, perform the rotating cut without damaging the semi-conductive water-
swellable tape underneath the aluminum laminate. > After removing the outer
sheath, three additional longitudinal cuts are required to place the grounding
grater. Split the outer sheath with the auxiliary tool ST285.
For insulation removal, go to page 22
11
Outer sheath removal
Universal cable stripper with fast locking system
Scan QR code for video demonstration or click here.
Universal cable stripper Ensto ST257 > Removes outer sheath of single core
cables with aluminum laminate. > Round and longitudinal cuts. > Hook for outer
sheath removal. > Blade depth adjustable by knob.
Instructions > Measure the cable diameter with a
Vernier caliper. > Adjust the tool according to the cable
diameter by knob. > Lock the tool. > Adjust the blade depth by knob. > Perform
the longitudinal cuts. > Switch to round cut and keep the
blade depth unaltered. > Perform the round cut.
Tips Longitudinal cut first. Round cut after.
Before the longitudinal cut: > Keep the cable as straight as possible. > Test
the depth of the blade in the first
50 to 60 mm from the cut edge of the cable. It is safe to test the tool there
because the insulation will later be removed to install the cable lug or
connector. > Make sure the cut doesn’t go through the semi-conductive water-
swellable tape under the aluminum laminate. This will grant the integrity of
the insulation and its screen along the cut. > Do not perform the cut on the
aluminum foil overlap. The extra thickness may make the cut ineffective.
Before the round cut: > When turning the blade 90 degrees
for the round cut, make sure the depth of the blade remains unaltered.
12
Outer sheath removal
Complementary tools
Ensto ST285 for outer sheath longitudinal cut. The tool splits the MV cable
outer sheath and aluminum laminate for a distance of 40 mm. Application ø is
16-60 mm.
Scan QR code for video demonstration or click here.
Ensto ST259 is an outer sheath spreading wedge that is also used to help open
or remove the outer sheath of single and three-core cables of different
constructions.
Scan QR code for video demonstration or click here.
Ensto ST286 is used to spread the outer sheath and/or aluminum laminate. It
does not harm the aluminum laminate or semi-conductive layer during spreading.
Scan QR code for video demonstration or click here.
Ensto ST310 is for fastening metallic cable ties on the cable’s outer sheath.
With the metallic ties, the grounding grater makes an earthing contact to the
aluminum laminate screen. The tool does the tightening and cutting of the
exceeding tie.
Scan QR code for video demonstration or click here.
13
Outer sheath removal
Plier for outer sheath
Scan QR code for video demonstration or click here.
Plier > Removes outer sheath of single- and
three-core cables with copper wires. > Fixed blade depth for round cut. >
Adjustable blade depth for longitudi-
nal cut. > Hook for sheath removal.
Instructions > Perform the round cut by rotating
the tool. > Adjust the blade depth and perform
the longitudinal cut. > If needed, use the wedge ST259 and a
hammer to spread the outer sheath. > Remove the outer sheath with the
help of the inbuilt hook.
Tips Round cut first. Longitudinal cut thereafter.
Using a Vernier caliper, measure the thickness of the outer sheath of the cable and choose a plier with a suitable depth of the fixed blade.
14
Outer sheath removal
Waterproofing
When installing heat-shrink or hybrid
accessories, grind the outer sheath to
1
provide a grip point to the heat-shrink
outer sealing tube. Waterproofing is
achieved by the sealing mastic and the
glue of the sealing tube. Both will melt
when heat is applied to shrink the outer
sealing tube.
Instructions
Grind the cutback of the cable outer
sheath according to installation instruc-
tions. Grinding should be performed
parallel to the cut of the cable (1).
Clean the cable outer sheath after
grinding to ensure correct adhesion
of the sealing mastic and the glue un-
2
der the outer sealing tube (2).
Make sure any cut around the outer sheath is smooth and straight, not to interfere with tools being used in further steps (e.g., insulation screen removal). Uneven shapes may cause the tools to bend and damage the screen of the insulation.
Always clean the outer sheath before removal
and after grinding it
Scan QR code for video demonstration or click here.
15
Outer sheath removal
Hot opening
1
Apply heat symmetrically Use a mid-to-high flame to heat the outer sheath. Keep the flame moving all the time around the cable and through the whole peeling length.
2
Cut and remove the outer sheath
Once the sheath is heated enough, use
the cable stripping string for the round
cut and drag it to the edge of the cable.
This will split the sheath in two and ease
the removal. Wear thick gloves to pro-
tect from burning.
3
Grind the metallic screen
Grind the aluminum laminate to re-
move traces of glue and outer sheath.
This grants a clean earth connection of
the screen.
4
Remove aluminum laminate
Place a constant force spring and remove
the unnecessary aluminum laminate.
16
Insulation screen
Insulation screen is also known as the semi-conductive layer. It prevents concentration of electrical field at the interface between the insulation and the metallic screen. It can be bonded or strippable. When terminating or jointing a medium-voltage cable, part of the insulation screen must be removed.
Bonded insulation screen Consists of a black cross-linked compound that requires rotating stripping tools for removal. To avoid dangerous concentrations of electric field, avoid sharp edges in the edge of the semiconductive layer. Grinding the insulation is recommended after removing a bonded insulation screen.
Strippable insulation screen Also known as “easy strip”. Not fully bonded to the insulation and must be strippable by hand. Rotating tools with adjustable depth length are recommended for its removal. The use of unguarded knives is forbidden due to the risk of damaging the insulation and causing discharges. Cables with strippable insulation screen require no grinding of the insulation after screen removal.
17
Insulation screen removal
Bonded semiconductor stripper
Scan QR code for video demonstration or click here.
Bonded semi-conductive stripper Ensto ST308 > Insulation screen removal tool
with
chamfered end.
Ball bearings for effortless turning. > No greasing of the core is needed. > Adjustable blade depth. > Stopper included.
Instructions > Place the stopper accordingly (if used). > Tighten the tool on
the cable with the
red knob. > Adjust the depth of the blade with
the screw. > Proceed with the rotating movement
for peeling. > Turn the red knob about 1/4 of a full
round before the stopper. > Proceed with the final cut.
Tips To avoid leaving traces of semi-conductive layer on the insulation: Make
sure the cable is as straight as possible before starting and test the tool in
the first 50 mm of the cable. Make sure that at least 1/3 of the strip is
insulation before proceeding.
Notice that irregularities in the shape of the stripped part reflects how bent
the cable is proportionally. Check the strip often and make sure there is a
part of insulation all over it. If there is a full black part, it means that
semi-conductive traces are still present on the insulation.
18
Insulation screen removal
Peelable non-vulcanized semiconductor stripper
Scan QR code for video demonstration or click here.
Peelable non-vulcanized semiconductor stripper Ensto ST260 > Peelable semi- conductive stripper. > Stopper clamp included. > Adjustable blade depth. > Adjustable cut angle.
Instructions > Place the stopper clamp accordingly. > Make two round cuts with
the blade
guide parallel to the edge of the tool. > Turn the blade guide 45° and pro-
ceed to cut upward by rotating to the end of the cable. > Start peeling the
strip until the semiconductive edge. > Carefully accompany with a gentle
pressure toward the edge of the cut when removing the final strip at the edge
of the screen.
Tips To avoid damaging the insulation: > Test the depth of the blade in the
first
50 mm of the cable. > Verify the distance between the stop-
per and the cutting line.
To smooth the insulation after peeling: If the use of fire is permitted, it is
possible to smooth the insulation surface from marks by using a flame. > Apply
a medium flame through all
the peeling length.
19
Additional comments on the insulation screen
Avoid sharp edges Sharp edges in the insulation screen is a common error. The transition between the screen and the insulation must be smooth, achieved by a straight final cut.
correct
incorrect
Avoid leaving traces of semiconductive layer When parts of the strip look
partially or totally black, it means that traces of the semi-conductive
insulation screen were left on the insulation. To avoid this, keep the cable
as straight as possible and follow the strip during the peeling, keeping at
least 1/3 of the strip as insulation. The higher the voltage class of the
cable, the bigger the proportion of insulation can be, up to a maximum of 1/2
of the strip.
How to fix mistakes If traces of black semi-conductive insulation screen are
still present on the insulation, remove them with a scrapper. Never try to
remove them by grinding, because conductive black particles will be spread all
over the insulation and cause discharge. Grinding of the insulation is
performed to smooth its surface after stripping all traces of the
semiconductive layer.
Scan QR code for video demonstration or click here.
20
Insulation
The insulation thickness is defined by the rated voltage of the cable. Cross- linked polyethylene (XLPE) and ethylene propylene rubber (EPR) are common insulation materials.
Extrusion Plastic polymeric insulated cables are three-layer extruded: >
Conductor screen: Semi-conductive,
between the conductors and the insulation material. > Insulation: High
resistivity > Insulation screen: Semi-conductive, between the insulation
material and the metallic screen.
Treating the insulation After removing the insulation screen, part of the
insulation is removed for connecting a lug or connector. The remaining peeled
insulation must have a smooth surface and may require grinding, depending of
the tool used and the skill of the installer. When jointing two cables, it is
recommended to chamfer the edge of the insulation.
The conductor screen is removed together with the insulation. When in place,
it ensures a good contact and fills any voids between the conductors and the
insulation, while diminishing the concentration of field at the surface of the
conductors. > Save the bags of the tubes, joint or
termination bodies to cover the insulation and use them after screen removal
and before grinding as protection for the insulation or the silicone body
parts. > When cleaning the insulation, always begin from the external side and
continue up to the screen. Never do the opposite, otherwise conductive
particles or dirt could be dragged to the insulation and cause discharge.
21
Insulation removal
Multifunction tool for outer sheath and insulation removal
Scan QR code for video demonstration or click here.
Multifunction tool Ensto ST281 > Removes outer sheath of single-core
cables with aluminum laminate. > Removes all types of polymeric insu-
lation. > Teflon pads for minimum friction. > Stopper included. > Adjustable
blade depth. > Adjustable blade angle.
Instructions > Clean the inner Teflon wards. > Put the tool in place and
fasten it
tightly. > Set the blade depth above the con-
ductor screen. > Place the stopper and lock it at the
desired peeling length. > Adjust the angle of the blade to its
minimum. > Rotate the tool to remove the insulation. > The stopper grants a
straight final
cut.
Tips > Clean the Teflon wards located in the
inner part of the tool to avoid damage to the insulation, caused by sand
particles or dirt that might be there after removing the outer sheath. >
Before proceeding with the cut, place the stopper into the multifunctional
tool at the desired peeling length. It is sufficient to set the blade depth
slightly over the conductor screen to prevent damage to the blade and the
shape of the conductors.
For outer sheath removal, go to page 11
22
Insulation removal
Ensto ST252 is designed to remove the cable insulation of 10 and 20 kV MV
cables with cross-section 25 up to 240 mm². Stripping length adjustable from
20 to 100 mm using the device built into the handle. Set including rigid case
with stripping inserts for cross-sections from 25 to 240 mm².
Scan QR code for video demonstration or click here.
Ensto ST280 is designed to chamfer the primary insulation near the connector
or lug in MV cables. This provides a smooth transition from insulation to
connector or lug for the accessories installed. The application range ø is
15-60 mm and the chamfer is 45°.
Scan QR code for video demonstration or click here.
Chamfering decreases the density of the electric field at the edge of the insulation. The results of a simulation using Comsol show a lower density in the chamfered insulation in Picture 1. On the other hand, Picture 2 shows a a higher density at the sharp edge of the unchamfered insulation.
From a mechanical perspective, chamfering is highly recom-
mended when installing cold-shrink joints. It prevents damage
on the silicone joint body if heavy objects (rocks for example)
hit the joints.
1
2
23
Installation grease is applied to the insulation to set the silicone bodies and to help positioning them
Additional comments on the insulation
Grinding, polishing and cleaning
Scan QR code for video demonstration or click here.
Grinding and polishing To avoid air gaps where discharges can occur, the insulation surface must be smooth. Use long and thin strips of grinding paper. Perform carefully and do not grind the insulation screen.
Cleaning Thoroughly clean the insulation, always toward the insulation screen. Never use the same side of a cleaning tissue twice. The insulation must be clean of conductive particles and dirt.
25
Conductors
Typical cross section values in medium-voltage underground cables range from 35 up to 1000 mm2. With stranded or solid conductors, cables are circular or sector-shaped.
Aluminum or copper Conductors are made of aluminum or copper, to carry current under normal, overload and short-circuit operating conditions. As copper is more conductive, it takes 65% more aluminum to electrically replace copper (1 mm2 of copper equals 1.65 mm2 of aluminum). On the other hand, aluminum is cheaper per ampere than copper and lighter in weight, allowing more length installation and requiring less jointing.
Classification Classification of cables is also made according to the
construction and shape of conductors:
Circular conductors are used in both single- and three-core cables. > Class 1
circular: Circular solid > Class 2 circular: Circular stranded
Sector-shaped conductors are used in three-core cables to minimize the cable
diameter. > Class 1 sector: Sector-shaped solid > Class 2 sector: Sector-
shaped stranded
Conductors are also designed to withstand mechanical stress when being pulled during installation.
Classification examples
(1) Class 2 circular aluminum stranded
(2) Class 2 sector copper stranded
1
2
26
Conductors
Cable lugs and connectors
Scan QR code for video demonstration or click here.
Cable lugs are used when terminating a cable. Connectors are used when
jointing two cables.
Scan QR code for bolt tightening sequence of the connector
Clamp device Ensto ST251 is used to hold the lug or connector while tightening the bolts. Especially suitable for underground shear head bolt connectors with diameters from 14 to 40 mm. Suitable for work on live parts with voltages up to 1000 V AC and 1500 V DC. Insulated in compliance with EN60900/IEC900 standards.
When installing a lug or a connector > Pay attention to the shape and cross
section of the conductors. Put the centering ring on if needed. > Brush the
conductors just before installing a lug or connector. > Use the clamp device
ST251 to hold the lug or connector. > Perform the pre-tightening and
tightening sequences, from the outer bolts to the inner ones. Scan the QR code
for a video demonstration. > Wrap the insulation with a plastic or fabric
before breaking the shear head bolts. > Clean the insulation thoroughly and
remove the conductive particles and dirt. > If there is a ground connector for
external grounding wires, do not connect it close to the joint bodies.
27
Brushing lowers the probability of additional heating of the lug or the connector by lowering the resistance at the connection point
Transition joints and paper-insulated cables
Transition joints are used to connect paper insulated cables to polymeric insulated cables.
Cellulose paper is not a good insulation material by itself, but the high
dielectric strength of the mineral oil used to impregnate the paper provides a
satisfactory insulation level in low, medium- and high-voltage applications.
Before polymeric insulated cables became a worldwide trend during the 1980s,
different types of paper-insulated cables were installed by utilities and
industries. This is why paper cables are still in service in many distribution
networks and installers are required to know how to work with them.
Installing transition joints from oilimpregnated paper cables on polymeric
insulated cables is the most typical task some installers may ever perform in
the field, therefore, it is important to be familiar with the types of paper
cables and how to handle them.
Handling old paper cables Paper-insulated cables do not require special tools,
but they do require more skill from the installer. Follow these
recommendations when handling old paper cables: > Manipulate the cable with
care be-
cause the armor may have been corroded, leaving the cable with no mechanical
protection. > Bend the phases very carefully. Cracking the paper insulation
will result in failure during operation. > Perform the installation until the
end after removing the lead or aluminum sheath to prevent moisture from being
absorbed by the cable. > Wear gloves while manipulating the lead sheath.
29
Parts of a paper insulated cable
Outer sheath / Serving coat Paper-insulated cables typically have a polymeric
outer sheath or bitumenimpregnated hessian tape as the most external layer.
For optimal removal of bitumen-impregnated serving coats, it is sufficient to
apply enough heat and then proceed to remove it by hand. A constant force
spring, PVC tape or screw clip can be used to have a fixed and straight cut at
the desired length. If the outer sheath is made of PVC or MDPE, refer to the
Plier for mediumvoltage cable outer sheath.
Armor and bedding The armor provides mechanical protection against crushing
forces and can also be used as a neutral conductor together with the cable
sheath. There are three ways to armor cables: > STA: Steel tape armor, used in
multi-
core cables (magnetic) > SWA: Steel wire armor, used in multi-
core cables (magnetic) > AWA: Aluminum wire armor, used in
single-core cables (non-magnetic) The reason behind using magnetic or non-
magnetic armoring is related to overheating. In three-core cables, the current
flowing induces a magnetic field
from each phase, but the vector sum is always close to zero, resulting in very
small induced currents in the armor. In single-core cables, non-magnetic
aluminum is used to prevent this from happening. In this procedure, the armor
is laid over the bedding, which is typically made of wrapped layers of paper
and bitumen hessian tape. The bedding serves as a surface for the armor and
protection for the sheath underneath and the laid-up cores.
For correct removal of armor and bedding, use a constant force spring to keep
the armor in place and a hacksaw to cut the armor. Once the outer sheath is
exposed, heat up the bitumen with a medium flame and then use wax help to
remove the bitumen from the sheath and clean it.
Sheath In most cases, an extruded sheath of lead or lead alloy is applied to
protect the paper insulation, but aluminum is also used. Connected to the
armor, it provides a path for fault and leakage current. The main advantages
of an extruded lead sheath are waterproofing and corrosion resistance, but on
the
other hand it has a limited short circuit capacity, it is made of an expensive
material and because of its toxicity, its use is being restricted. A lead
sheath can be removed with a knife or with a Plier for medium-voltage cable
outer sheath.
Belt insulation, belt screen and fillers The belt insulation and fillers are
typically made of paper, impregnated with a mass-impregnated non-draining
(MIND) compound. The belt screen is made of carbon paper tapes.
Insulation screen and insulation The impregnated paper tapes are helically
lapped around the conductors up to the thickness defined by the voltage level.
In belted cables, there is no insulation screen at all, but in type H and HSL,
it is made of carbon paper tapes and a copper tape or aluminum foil.
30
Types of medium-voltage paper-insulated cables
Belted
Serving coat
Sheath Bedding Armor
Core insulation Belted insulation Belted insulation screen
Conductor Conductor screen
Unscreened phases The unscreened phases are laid up and insulated to withstand
full line-to-line voltage.
Common lead sheath An additional layer of oil-impregnated insulation paper
known as the belt layer, hence the name, is applied around the three phases
and then the cable is lead-sheathed.
Armor and serving coat If the cable is armored, a layer of bedding for the
armor is added together with a serving coat, which is the most external layer
that provides protection from the environment. If the cable is unarmored, then
a bitumen layer is added on top of the lead sheath to prevent corrosion and a
PVC outer sheath is extruded.
Commonly 12 kV
31
Types of medium-voltage paper-insulated cables
Type H
Filler
Serving coat
Sheath Bedding Armor
Commonly 36 kV
Core insulation Metallic screen
Conductor Conductor screen
Individually screened phases The insulation of each phase is individually
screened with a metallic laminate. The cores of the cable are insulated to
withstand full line-to-earth voltage, and laid so that the metallic screens
are in contact with each other.
Common lead sheath Underneath the lead sheath, a layer of oil impregnated
paper is added enclosing the phases and the filler parts.
Armor and serving coat If the cable is armored, a layer of bedding for the
armor is added and a serving coat as the most external layer provides
protection from the environment. If the cable is unarmored, then a bitumen
layer is added on top of the lead sheath to prevent corrosion and a medium-
density polyethylene (MDPE) outer sheath is extruded.
32
Types of medium-voltage paper-insulated cables
Type HSL
Filler
Bedding Armor Serving coat
Sheath
Core insulation Insulation screen
Conductor Conductor screen
Individually screened and sheathed phases Insulated to withstand full phase-
to-earth voltage, each core is built up as an individual single-core cable and
then enclosed by a bedding made of wrapped taped paper and bituminized hessian
tape. Each phase is individually screened and sheathed.
Armor and serving coat The cable is armored with metallic wires of plates. An
extruded outer sheath made of PVC, or a bitumen impregnated hessian tape as
serving coating, protects the cable from the environment.
Commonly 36 kV
33
Preparation before the installation
Accessory kit Verify that the kit contains all the components listed in the
bill of materials.
Always remember to: > Wash your hands before manipulat-
ing the components of the kit > When jointing two cables, place all
the tubular components in one cable before cable preparation
Installation site The conditions of the installation site may suddenly change due to weather conditions. Expect those changes and be prepared with plastic mattresses, portable roofs, lanterns, pallets and cable stands.
Cable preparation tools > Check the conditions of the tools and
the availability of spare parts beforehand. > If a hybrid or heat-shrink
accessory will be installed, check the gas level of the torch. > Keep the
tools in a clean tray.
Ensto ST277 cable joint stand locking mechanism keeps cable ends in place
during cable preparation and makes jointing
easier
35
Installation errors
Example of mistakes that cause faults in cable accessories
Sharp bolt Shear head bolts break when the right torque is achieved. Always
use the correct tools for tightening the bolts and never try to break the
bolts using other methods. Sharp edges or other shape irregularities will
cause the accessory to fail. This is not a problem when installing Ensto step-
less screw connectors Once the screw breaks, a semi-conductive cover is placed
on top of it.
Joint body not centered In the worst, critical areas of the cable are left
without any stress control and discharge eventually occurs.
Irregular edge of the insulation screen When the edge of the black semi-
conductive layer has sharp edges or an irregular shape, a dangerous
concentration of electric field occurs in the most critical part of the cable.
This is particularly dangerous in heat-shrink accessories.
Air gaps in stress control mastic When stress control mastic is not melted or
was not applied correctly, air gaps remain and discharge occurs.
36
Tubes shrank asymmetrically Flame must be in constant movement and applied
symmetrically all around the heat-shrink tubes.
Grinding the insulation screen This cause conductive particles to spread all
over the insulation, causing partial discharges.
Dirt between tubes If the outer sheath is not clean or the tubes are not
cleaned after shrinking, sand, dirt and/or small stones can be trapped between
tubes and cause severe damage.
Mastics pulled out from original position When positioning the tubes, pay
attention not to pull or drag the mastics underneath. The picture shows an
area of the insulation screen left unprotected when part of the stress control
mastic was pulled away from its position while placing the tube.
37
Installation errors
Example of mistakes that cause faults in cable accessories
Sand and dirt Installation has high cleanliness requirements. Respect them.
Treeing marks Discharge occurs in air gaps on untreated insulation. The damage
of this discharge is progressive and eventually causes the accessory to fail.
38
Ensto Pro
and Installer Certification
Ensto offers more than products: a complete package with reliable solutions, professional service, and customized support. We want to share our experience in electricity network building and have created Ensto Pro training and Installer Certification concepts.
Ensto Pro is a technical training concept targeted to Enstos’ customers, partners and our own personnel. The aim is to support sales and create loyal customer relations by sharing knowledge. We wish to learn from customer experiences and truly understand customers’ requirements, thereby becoming able to develop our products to best meet those precise needs.
happen in the field or in virtual. Also, we are ready to teach about a host of topics as customer needs and wishes dictate. We also arrange, or are involved in, sessions attended by professionals from various institutions, such as cable manufacturers and energy-market authorities. By offering all the necessary information in one session, we save time and energy. We care about your success.
6000 units yearly zero installation faults The Finnish DSO Enerke has already certificated of all their installers. The original certificates were valid for five years and in 2020 it was time to re-certify. Enerke sees certification very important and certification is in place to make sure that everyone can produce top quality.
Ensto Pro training is unique: > Local service in the local language. >
Customized trainings. > Consistent and engaging training
methods and presentations. > Easy-going and easily approachable
professionals. > Emphasis on two-way learning.
Customer benefits from Ensto Pro training: > Time, cost, and energy savings. >
Fewer installation errors. > Confidence and motivation. > The opportunity to
have an influence. > New perspectives.
Variety of Training Types Our customer training ranges from small installation
sessions to large lecturetype events. Installation trainings can
Ensto Installer Certification Installer Certification means a screening test
for the installation of Ensto’s low and medium voltage underground cable
accessories, which aims at the correct installation. The starting point is the
need for network companies to reduce failure interruptions due to installation
errors, which is a global problem.
Installer Certification has many benefits for the DSO’s, contractors and
installers. > Correctly installed solutions and longer
lifespan. > Reliability to the network. > Time and cost savings avoiding
elec-
trical outages. > Motivated professionals. > Professional know-how. > Extended
warranty. > Certified quality.
Enerke terminates yearly 2000 units of 3-phase cables resulting to 6000
terminations. In normal year there has been not a single fault. Enerke
believes in Ensto as a partner that helps in many ways to achieve the high
quality and reliability criteria they have set for themselves.
Ask more of Ensto Pro training and Installer Certification from sales.
39
Cable tools
Our selection includes peeling tools for the insulation, insulation screen and
sheath of medium voltage cables.
Medium voltage insulation removal tools
Product code ST252 ST252.1 ST261 ST266.10 ST267.10 ST269.10 ST270.10 ST271.10 ST272.10 ST273.10 ST265 ST266 ST267 ST268 ST269 ST270 ST271 ST272 ST273 ST274 ST274.1
GTIN 6418677457418 6418677457425 6438100314446 6438100330286 6438100330293 6438100340346 6438100330309 6438100330316 6438100330323 6438100330330 6438100316099 6438100314453 6438100316105 6438100316112 6438100316129 6438100316136 6438100316143 6438100316150 6438100316167 6438100316174 6438100330354
Description Insulation removal set for 20 kV cables Spare blade for ST252 Insulation stripping handle for inserts ST265-273 Insulation removal insert 10kV 35 mm² for ST261 Insulation removal insert 10kV 50 mm² for ST261 Insulation removal insert 10kV 95 mm² for ST261 Insulation removal insert 10kV 120 mm² for ST261 Insulation removal insert 10kV 150 mm² for ST261 Insulation removal insert 10kV 185 mm² for ST261 Insulation removal insert 10kV 240 mm² for ST261 Insulation removal insert 20kV 25 mm² for ST261 Insulation removal insert 20kV 35 mm² for ST261 Insulation removal insert 20kV 50 mm² for ST261 Insulation removal insert 20kV 70 mm² for ST261 Insulation removal insert 20kV 95 mm² for ST261 Insulation removal insert 20kV 120 mm² for ST261 Insulation removal insert 20kV 150 mm² for ST261 Insulation removal insert 20kV 185 mm² for ST261 Insulation removal insert 20kV 240 mm² for ST261 Insulation removal tool ø 15-52 mm Spare blade for ST274
Insulation screen removal tools
Product code ST250 ST250.1 ST308 ST308.1
GTIN 6418677457388 6418677457395 6438100324117 6438100330026
ST260
6438100313128
ST260.1
6438100317935
Description Bonded insulation screen removal tool 10-52 mm Spare blade for ST250 Bonded insulation screen removal tool 18-60 mm Spare blade for ST308 Peelable (non-vulcanized) insulation screen removal tool ø 16-41 mm Spare blade for ST260
40
Cable tools
Outer sheath removal tools
Product code GTIN
ST257
6438100311940
ST257.1
6438100321383
ST281
6438100320232
ST281.1
6438100330002
ST285
6438100320270
ST285.1
6438100330019
ST291
6438100329990
Description Outer sheath/aluminium laminate removal tool ø 16-54 mm Spare blade for ST257 Outer sheath/aluminium laminate removal tool ø 16-40 mm Spare blade for ST281 Outer sheath/aluminium laminate splitting tool ø 16-60 mm Spare blade for ST285 Outer sheath/aluminium laminate removal tool ø 16-58 mm
Cable stands
Product code GTIN
ST277
6438100317089
Description Cable jointing stand
Additional tools
Product code GTIN
ST251
6418677457401
ST259
6438100312367
ST286
6438100320287
ST258
6438100312015
ST310
6438100327903
ST280
6438100318666
ST280.1
6438100324483
Description Holding tool for connectors/lugs Wedge for spreading the outer sheath and aluminium laminate Tool for spreading the outer sheath and aluminium laminate Metal tie tightening tool Metal tie fastening pliers Insulation chamfering tool ø 15-60 mm Spare blade for ST280
41
Notes
42
Ensto DSO/ENG/05/2021
Ensto Finland Oy Ensio Miettisen katu 2, P.O. Box 77 FIN-06101 Porvoo, Finland
ensto@ensto.com
ensto com
References
Read User Manual Online (PDF format)
Read User Manual Online (PDF format) >>