E.C.S.
INFORMATION SECTION
Issued 06-01-07
UNDERGROUND SPLICES AND TERMINATIONS
Section WST00
Page 1 of 1
INDEX
SECTION WST01: GENERAL
ELECTRICAL STRESS ON PRIMARY CABLE ………………………… Page 1
CAUSES OF FAILURES ………………………………………………….. Page 2
GROUNDING OF BUSHINGS, PROTECTIVE CAPS AND ELBOW
TERMINATORS ……………………………………………………………. Page 2
3M COLD-SHRINK CABLE JACKET SEAL KITS ……………………… Page 3
SECTION WST02: TAPES
DESCRIPTION AND APPLICATION ……………………………………. Page 1
SECTION WST03: CABLE END PREPARATION
REMOVAL OF JACKET …………………………………………………… Page 1
REMOVAL OF INSULATION TO EXPOSE CONDUCTOR …………… Page 1
REMOVAL OF SEMI-CONDUCTING INSULATION SHIELD ………… Page 2
CLEANING CABLE ……………………………………………………...... Page 2
SECTION WST04: ELBOWS
GENERAL ………………………………………………………………….. Page 1
APPLICATION ……………………………………………………………… Page 2
INSTALLATION OF 600A ELBOW TERMINATORS ………………….. Page 3
PRECAUTIONS ……………………………………………………………. Page 5
OPERATION AND MAINTENANCE …………………………………….. Page 5
PARTIAL VACUUM FLASHOVERS …………………………………….. Page 5
SECTION WST05: SPLICES
PRIMARY CABLE SPLICES ……………………………………………… Page 1
E.C.S.
INFORMATIONAL SECTION
Issued 06-01-07
UNDERGROUND SPLICES AND TERMINATIONS
Section WST01
Page 1 of 3
GENERAL
1. ELECTRICAL STRESS ON PRIMARY CABLE
a. Dielectric Stress
Concentric neutral cable consists of a conductor, conductor or strand shield, insulating medium,
insulation shielding and a shield drain (neutral) assembly. The design of the cable using these
elements is primarily based on the control of the two types of electrical stresses which are radial
within the insulation wall and on its surface. These dielectric stresses are dependent on the
voltage gradients between the conductors and can be represented as flux lines and
equipotential lines.
1) Figure 01-1 Flux Lines represents the flux lines, radial stress on a cross-sectional plane.
These stresses diminish in intensity as the lines diverge and approach the ground electrode
outer shield. Maximum stress occurs at the conductor shield.
2) Figure 01-2 Equipotential Stress Lines represents equipotential lines which are points of
equal stress magnitude at a constant distance from the conductor: The highest stress level
is closest to the conductor and is zero at the outer surface of the insulation.
Figure 01-1 Flux Lines
Figure 01-2 Equipotential Stress Lines
b. Theory of Stress Control When Splicing and Terminating
It is obvious that every cable run must have two ends. The shielded power cable has a
conductor which is energized at line potential and a grounded shield separated from the
conductor by a relatively thin wall of insulation. This distance is so small that the voltage would
cause flashover from conductor to shield at the cable ends if the cable was energized.
Therefore, when the cable is terminated, it is necessary to remove the shield from the proximity
of the conductor. When the shielding is removed from the insulation, there is a considerable
change in the dielectric field. The radial and longitudinal stresses are no longer completely
controlled by the shield. The result is a concentration of these stresses at the termination of the
cable shield. This concentration of stress results in the dielectric strength of the cable system
being minimized at this point. This could result in dielectric failure unless measures are taken to
control the stress and reduce it to tolerable limits.
Section WST01
Page 2 of 3
E.C.S.
INFORMATION SECTION
GENERAL
Issued 06-01-07
UNDERGROUND SPLICES AND TERMINATIONS
Methods for controlling and reducing this stress are referred to as stress relief. One method of
accomplishing this is to gradually increase the wall thickness of the insulation beyond the
termination of the cable shield. This insulation build-up is shaped in the form of a cone. The
cable shielding is then extended up the surface of the cone and terminated at a point of
increased insulation thickness over that of the original cable. The stress concentration is thereby
reduced to an acceptable level. Another method is the use of high dielectric materials which
reduces the stress concentration at the end of the shield, without increasing the insulation
thickness. Stress relief can be constructed with hand applied insulating and conducting
shielding tapes, heat-shrinkable or cold-shrinkable materials, or with factory molded devices.
2. CAUSES OF FAILURES
Following are common causes of failed splices and terminations:
•
Contamination from dirt, moisture or petroleum products
•
Not removing semi-conducting insulation shield layer from insulation
•
Inaccurate dimensioning
•
Improper cleaning of insulation (use of conducting solvents or abrasives)
•
Nicks in insulation or improper tapering (penciling)
•
Leaving jagged shield edges
•
Sharp burrs left on conductor or connector
•
Sharp bending at or near splice or termination
•
Improper or loose connections or broken strands
•
Gaps or voids left at junction with cable components
•
Improper taping
•
Noncompatible materials
NOTE: Be sure to tie the concentric neutral wires of primary cable as close to the cable
termination device as possible to prevent failures due to cable tracking. Tie the
concentric neutrals with one of the neutral wires. DO NOT USE TAPE as it adds
unwanted resistance to the ground path.
3. GROUNDING OF BUSHINGS, PROTECTIVE CAPS AND ELBOW TERMINATORS
To eliminate concerns with corona, follow the grounding tab instructions that come with
padmounted equipment and rubber-molded cable termination accessories.
Corona is the result of voltage differences between parts of the system. A "static" charge builds up
on the outside insulating layers of all devices operating at higher voltages, such as on our primary
distribution systems. A drain wire connecting these outside layers bleeds off this charge.
If drain wires are not provided, the charge will build and, under moist conditions, will bridge air gaps
resulting in corona. Corona is sometimes visible as a blue light, and usually creates radio
interference.
Issued 06-01-07
E.C.S.
INFORMATION SECTION
UNDERGROUND SPLICES AND TERMINATIONS
Section WST01
Page 3 of 3
GENERAL
Also, if left to continue for long periods of time, part of the corona discharge will erode the surfaces
it travels over, especially those of rubber and plastic. Our distribution cables, elbows, protective
caps and bushings have an outer surface that is rubber or plastic, impregnated with semiconducting carbon. This outside surface will conduct small charges to the drain or neutral wires.
The grounding tabs and drain wires are designed to keep the discharge currents very small,
thereby eliminating the problem.
4. 3M COLD-SHRINK CABLE JACKET SEAL KITS
There are two methods of installing these seals that are used around the company. There are
separate instruction sheets enclosed in the kit for each method. The diagrams shown on the first
page of each set can quickly identify the proper instructions.
The 3M standard instruction sheet shows the neutral wires folded back over the outer cable jacket
and the seal applied over the neutral wires and the cable semi-conducting insulation shield.
The "non-foldback neutral wire sealing" instruction sheet details how to install the seal without
bending the neutral wires back over the jacket. This method is used when the outer jacket is
stripped back to make the cable more flexible. In this case, the neutral wires are left in position
against the cable semi-conducting insulation shield. The seal is slid over the cable and down to the
jacket with the lower part of the seal covering the end of the jacket while the upper part seals over
the neutral conductors.
(END)
Issued 08-01-08
E.C.S.
INFORMATION SECTION
UNDERGROUND SPLICES AND TERMINATIONS
Section WST02
Page 1 of 2
TAPES
1. DESCRIPTION AND APPLICATION
This section covers the description and application of certain tapes on underground distribution
cable.
a. Electrical Tape (Item ID 109499)
A black vinyl (PVC) electrical tape specifically designed for application in cold weather. Used
frequently as a protective outer covering (re-jacketing) on spliced low and medium voltage
power cables and terminations because of its resistance to acids, alkalines, salt, etc. DO NOT
APPLY IT DIRECTLY OVER SEMICONDUCTING SHIELDS SINCE THE ADHESIVE CAN
ADVERSELY AFFECT RESISTIVITY. Also used for insulating wire and cable splices and
terminations rated 600V maximum. Minimum application temperature is 0°F (18°C) and
maximum operating temperature is 220°F (105°C).
b. Rubber Shielding Tape (Item ID 104284)
EPR-based semiconducting self-fusing rubber tape utilized over spliced connectors on medium
voltage power cable to provide a continuation of the extruded conductor shield and to round out
connections to terminal lugs. Also the tape provides continuation of the insulation shield across
medium voltage (taped) splices and to the apex on conventional (taped) stress cones. The tape,
rated 266°F (130°C), has stable conductivity over a wide temperature range and is compatible
with PE, XLPE, EPR, PVC, butyl and oil-based rubber insulated cables.
c. Rubber High-Voltage Insulating Tape (Item ID 109990)
Self-fusing, corona resistant, 266°F (130°C) rated EPR-based tape for use on bus bar, electrical
connections and all extruded solid dielectric insulated cables (PE, XLPE, EPR, PVC, butyl
rubber). Provides insulation up to 69 kV, as well as moisture sealing and jacketing of splices,
terminations, connections, etc.
d. Track-Resistant Tape (Item ID 105606)
Self-fusing, silicone-rubber, track-resistant tape used as an overwrap to convert stress cone
terminations to outdoor service. Also used to provide track-resisitant finish on contaminated
indoor locations. Suitable on all types of cable.
e. Sealing Tape (Item ID 122346)
All weather, black, mastic, self-fusing, rubber sealing tape for molding around irregular shapes
to provide moisture and corrosion protection. Continuous operating temperature
rating of 194°F (90°C) with overload rating of 266° F (130°C). Should be overwrapped with
vinyl electrical tape Item ID 109499.
f.
Friction Tape (Item ID 102837)
Black, friction, general purpose tape for overwrapping low voltage splices, etc.
Section WST02
Page 2 of 2
E.C.S.
INFORMATION SECTION
TAPES
Issued 08-01-08
UNDERGROUND SPLICES AND TERMINATIONS
g. Marking Tapes (See List Below)
Colored tapes for temporarily marking measurements, etc., when splicing and terminating cable.
DO NOT LEAVE THIS TAPE ON THE CABLE.
Color
Item ID
White
109934
Brown
107421
Orange
105467
Yellow
100915
Red
104776
Blue
109326
Green
120588
h. Fire and Electric Arc Proof Tape (Item ID 109566)
The formulation of 77 Tape allows the manufacturing of an unsupported elastomer that expands
in fire to provide a thick insulating firewall between the cable and fire. It is thin, flexible and
conforming, wrapping easily around irregularly-shaped accessories. It is self extinguishing and
arc resistant.
(END)
Issued 06-01-07
E.C.S.
INFORMATION SECTION
UNDERGROUND SPLICES AND TERMINATIONS
Section WST03
Page 1 of 3
CABLE END PREPARATION
These guidelines are for preparing underground cable ends for splicing and terminating. These
guidelines serve to supplement, but should not replace the manufacturers’ instructions for splices and
terminations.
1. REMOVAL OF JACKET
For increased flexibility and reduced stress at the point of termination, the jacket may be removed
an appropriate distance from the end of the cable.
Use the cable jacket stripper/banana peeler tool (Item ID 106764) to make a 360° ring-cut in the
jacket. Then make a straight-cut from the ring-cut to the end of the cable. At a 3-4 inch distance
from the end of the cable, use a hook knife to cut completely through the jacket to the concentric
neutral. Spread the jacket and install the stripping wedge between the jacket and the concentric
wire. Push the wedge to the 360° ring-cut, making sure the wedge does not travel under the
concentric wire. Peel the jacket to expose concentric wires.
ALTERNATIVE
Our primary underground distribution cable specification was revised in 2004 to require two (2)
Kevlar nylon threaded rip cords embedded under the jacket, spaced 180-degrees apart* and
running longitudinally along the entire length of the cable. The Standards Advisory Team
unanimously recommended adding this requirement to make the jacket easier and safer to strip off
when making splices or terminations. The team also recommended keeping the requirement for the
water-swellable powder under the cable jacket (introduced in 2003).
The jacket must be cut back far enough from the end of the cable to expose the rip cords. Once
exposed, use needle-nose pliers to grip and pull (or rip) the nylon cords through and thereby
splitting the jacket. The jacket can then be peeled off to the length desired.
*Note: The manufacturing plant’s ability to keep the two rip cords 180–degrees apart the entire
length of the cable is impractical. The reason for this is that the rip cords may get caught on the
concentric neutral wires in the process of laying them on the cable, causing them to spiral around
the outside. Keep this in mind when locating the rip cords for jacket stripping. The Standards
Advisory team was aware of and experienced this during the cable field trials, but did not find it to
cause significant problems.
2. REMOVAL OF INSULATION TO EXPOSE CONDUCTOR
Clamp the end of the cable in the speed stripper tool (Item ID 101816). Then visually check and
adjust the depth of the blade to avoid nicking the conductor. Make a spiral-cut to the distance
required in the manufacturer’s instructions. At this point, move the blade from spiral to square-cut
and make a 360° ring-cut. Wire brush the conductor before removing the semi-conducting shield to
prevent contamination of the insulation.
Section WST03
Page 2 of 3
E.C.S.
INFORMATION SECTION
CABLE END PREPARATION
Issued 06-01-07
UNDERGROUND SPLICES AND TERMINATIONS
3. REMOVAL OF SEMI-CONDUCTING INSULATION SHIELD
Starting at the manufacturer’s required distance, install the semi-conductor stripping tool (Item ID
102977) onto the cable. Start with a square-cut and make a 360° ring-cut. Use a little silicone
grease on the blade to aid a smooth and quality cut. Adjust the tool to the spiral-cut setting and
rotate the tool to the end of the cable.
Caution: Make sure the blade depth is properly set to prevent scoring the insulation.
Caution: Install the tool so when it is changed from a straight to a spiral-cut style, the spiral-cut will
travel to the end of the cable.
Carefully remove the semi-conductor from the insulation by using a small needle-nose pliers. Be
careful not to damage the insulation. After the semi-conducting shield has been removed, check
for nicks and cuts by running your thumbnail along the surface of the insulation. See Cable
Cleaning Method 2 if nicks or cuts are detected.
4. CLEANING CABLE
Minor scratches on the insulation must be buffed. Cuts or gouges into the insulation necessitate
removal of insulation to that point and restarting. All conducting material must be removed from the
creepage area. Do not loosen remaining shield beyond the cut-off point either by allowing flaring or
by solvent flowing under the shield. Make cuts square, trim away raveling or jagged edges.
Utilize Cleaning Methods 1 or 2 outlined below, as appropriate, for cleaning the exposed insulation
surface after having removed the cable jacket and/or the semi-conducting insulation shield. Method
2 may be required if a line or mark is left on the surface of the insulation when removing the semiconducting insulation shield.
a. METHOD 1 - Solvent Wipe
1) After removing the semi-conducting insulation shield, clean the finished insulation surface by
wiping it with a clean, lint-free, dry cloth (Item ID 122096) which has been moistened with
the standard approved cable-cleaning solvent (Item ID 120377).
a) Rub briskly over the entire insulation surface. TAKE CARE not to get the solventmoistened cloth in contact with the semi-conducting shield. The solvent will dissolve and
extract some of the semi-conducting filler (carbon black) material, smearing it over the
insulation surface.
b) Repeat the cleaning operation, using fresh clean sections of the cloth, until it comes
away clean after the final wiping.
2) Allow the surface to dry before proceeding with the splice or termination, being sure to
protect the prepared cable from contamination.
Issued 06-01-07
E.C.S.
INFORMATION SECTION
UNDERGROUND SPLICES AND TERMINATIONS
Section WST03
Page 3 of 3
CABLE END PREPARATION
b. METHOD 2 - Abrasive Wipe
When the semi-conducting insulation shield is peeled from the insulation, a fine mark or line may be
left on the insulation surface. If these marks occur, they can be easily removed as follows:
1) Lightly sand the surface in a circumferential motion with a NON-CONDUCTING 120-grit abrasive
cloth (Item ID 105514).
CAUTION: CONDUCTIVE, METALLIC GRIT CLOTH, SUCH AS ALUMINUM OXIDE, MUST
NOT BE USED!
2) Follow-up and complete the abrasive wipe with the solvent wipe from METHOD 1.
(END)
Issued 08-01-08
E.C.S.
INFORMATION SECTION
Section WST04
Page 1 of 6
UNDERGROUND SPLICES AND TERMINATIONS
ELBOWS
1. GENERAL
a.
200A Elbow/Bushing Well System
ELBOW
1-1. Creep path integrity at the cable-elbow interface.
1-2. Stress relief. 1-3.
External shield. 1-4.
Internal shield.
1-5. Creep path integrity at the bushing elbow interface. 1-6.
Electrical circuit.
1-7. Voltage test point 18. Grounding point.
BUSHING
2-1. Creep path integrity. 22. Electrical circuit. 2-3.
Creep path integrity. 2-4.
External shield.
BUSHING WELL"FLOWER-POT"
3-1. Creep path integrity.
3-2. Conductive rubber ring.
3-3. Stainless steel flange and hold-down brackets. 3-4.
Electrical circuit.
Figure 04-1 Elbow/Bushing Well System
b.
Rating for 200A Elbow Terminators
Description
15KV Elbow Terminators
25KV Elbow Terminators
Standard Voltage Class
15 kV
25 kV
Maximum Phase-to-Phase
14.4 kV
26.3 kV
Maximum Phase-to-Ground
8.3 kV
15.2 kV
Basic Insulation Level (BIL)
95 kV
125 kV
Continuous Load
200A rms
200A rms
Switching
10 operations at 200A/14.4 kV
10 operations at 200A/26.3 kV
Fault Closure
10,000A rms symmetrical at
14.4 kV for 0.17 secs.
10,000A rms symmetrical at
26.3 kV for 0.17 secs
E.C.S.
INFORMATION SECTION
Section WST04
Page 2 of 6
ELBOWS
Issued 08-01-08
UNDERGROUND SPLICES AND TERMINATIONS
2. APPLICATION
The following table lists the correct elbow terminator and spare parts to use for the
specified conditions.
Table 04-1
200A ELBOW TERMINATORS
Cable Size
Voltage Rating
Cable
#2 Solid
Item ID
Elbow
Bushing
15 kV
(2)
Probe
109110
15 kV
103969
Connector
None
108995
(1)
25 kV
#1 Solid and
#2 Stranded
121179
100269
15 kV
1/0
25 kV
100340
150723
15 kV
106450
3/0
102867
103203
108995
15 kV
-----25 kV
123567
102332
15 kV
103203
108995
4/0
104033
103485
25 kV
25 kV
600A ELBOW TERMINATORS
Cable Size
Voltage Rating
Cable
Bushing
1/0
108524
(3)(4)(5)
Item ID
Elbow (2)
120537
15kV
15kV
25 kV
25 kV
102998/(121764)*
4/0
125113
500 kcmil
15 kV
15 kV
104989
102142/(120002)*
103021
125114
1000 kcmil
25 kV
25 kV
15 kV
15 kV
109459
120758
125115
25 kV
25 kV
120302
For Maintenance only on 220 mil insulated cable.
Source:
Alliant Electrical
Standards Created: 10-94
Revised: 03-05
103203
Issued 08-01-08
E.C.S.
INFORMATION SECTION
UNDERGROUND SPLICES AND TERMINATIONS
Section WST04
Page 3 of 6
ELBOWS
NOTES:
(1) For #1 solid or #2 stranded 15 kV cable to a 25 kV bushing application, use 25kV elbow terminator
Item ID number 150723, or replace the 25 kV bushing with a 15 kV bushing and use 15 kV elbow
terminator Item ID 103969.
(2) Do not place a cable with a smaller insulation diameter than the elbow terminator is designed to
accommodate. The resulting air gap between the cable insulation and the elbow stress relief layer
will cause a premature failure due to arcing and tracking along this interface.
(3) 600 A Elbow terminators include the following items:
•
T-Body Elbow Housing with Test Point
•
Cable Size Adapter
•
Aluminum Conductor Connector
•
200 Amp Insulating Protective Cap with Ground
•
200 Amp Loadbreak Aluminum Tap Plug
•
Tin-Plated Aluminum or Copper Alloy Equipment-Bushing Connection Stud
(4) A 200A elbow terminator or arrester may be installed on the 200A tap plug interface. When this is
done, return the 200A insulating protective cap to stock under Item ID 105193 (if 25 kV) or Item ID
101546 (if 15 kV).
(5) Installing Tool (Elastimold)
The hex installing tool is designed to shear at the ring-cut when the recommended installing torque
is reached. The hex rod can then be used for removal of the elbow assembly should disassembly
be required in the future. If reassembly is attempted with a hex rod (missing the ring-cut), the
recommended installing torque must be applied to assure a reliable connection.
3. INSTALLATION OF 600A ELBOW TERMINATORS
There are two brands of 600A elbow terminators on standards. The basic difference between the
two brands is how they connect to the apparatus bushing. The Cooper assembly uses an internal
nut that threads onto a stud that is pre-installed in the apparatus bushing. The Elastimold elbow has
an internal bolt that threads directly into the apparatus bushing.
The installation of both the Elastimold "Stick-Op" and the Cooper "T-OPII" elbows are summarized
below.
a. COOPER "T-OPII" INSTALLATION SUMMARY
1) Cut back the cable jacket, semicon and insulation from the cable end following the elbow
manufacturer's instructions and the guidelines found in ECS Information Section WST03,
Splices and Terminations - Cable End Preparation.
2) Install the cable jacket seal (not part of the elbow kit) on the cable, lube the cable insulation
and the inside of the elbow's cable adapter and install on the cable. Then place the threaded
eye compression connector on the conductor. Align the connector with the eye facing the
bushing and crimp.
3) Lube the t-body and exterior of the cable adapter and slide the t-body over the connector
and cable adapter.
E.C.S.
INFORMATION SECTION
Section WST04
Page 4 of 6
ELBOWS
Issued 08-01-08
UNDERGROUND SPLICES AND TERMINATIONS
4) Insert a 5/16" t-wrench tool into the Load Reducing Tap Plug (LRTP), insert the LRTP into
the t-body and carefully engage the threaded eye of the conductor connector using the
alignment segment on the end of the LRTP.
5) Turn the t-wrench (LRTP will turn with wrench) until positive stop is felt. Continue turning
until the shear pin breaks (the alignment segment may fall out before the pin shears) and
wrench turns freely. The LRTP is now fully seated against the connector. Remove the
alignment segment if it has not come off and out.
6) Remove the t-wrench from LRTP and insert a 5/16" hex torque tool. Push lubed t - body /
LRTP assembly onto the lightly lubed apparatus bushing. Carefully engage threads of LRTP
nut with stud threads. Tighten until 20-25 ft-lb of torque is achieved. Remove torque tool and
install insulated cap on LRTP. Attach insulated cap and elbow body drain wires to ground.
b. ELASTIMOLD "STICK-OP" INSTALLATION SUMMARY
1) Installation order is the same as the Cooper elbow until mounting onto the apparatus
bushing (1-5 above). However, a 3/8" t-wrench or an Elastimold 600AT tool is required to
install the LRTP in the t-body elbow and onto the threaded eye conductor connector. It is not
necessary for the LRTP to turn while being threaded onto the conductor connector.
2) The "Stick-Op" assembly does not require a stud in the bushing, remove the bushing stud if
the apparatus is so equipped.
3) Insert a 5/16" hex torque tool or Elastimold 600AT torque tool into the LRTP and engage the
free turning bolt. Push the lubed t-body / LRTP assembly onto the lubed apparatus bushing.
Carefully engage threads of LRTP bolt with internal threads of the bushing. Tighten until
proper torque is achieved (20 ft-lb or until 600AT tool slips). Remove tool and install
insulated cap on LRTP. Attach insulated cap and elbow body drain wires to ground.
c. TOOLS
Tool
Cooper (Item ID)
Elastimold
T-Wrench
2637659B03 (105167)
Included with kit
5/16 ” Hex Torque Tool
2637686B02M (109511)
N/A
5/16 ” – 3/8 ” Torque Tool
None
600AT
Issued 08-01-08
E.C.S.
INFORMATION SECTION
UNDERGROUND SPLICES AND TERMINATIONS
Section WST04
Page 5 of 6
ELBOWS
4. PRECAUTIONS
a. Always follow the manufacturer's installation instructions.
b. On all elbow terminator installations, one strand of the concentric neutral should be fed through
the eye of the elbow, located at the base of the terminator throat, and connected to ground. This
serves to bleed off any leakage current that may exist on the molded surface.
c. Use silicone grease Item ID 109464 when mating with a bushing insert. Do not use Item ID
120734 as it does not have the dielectric properties required.
d. The following information is edited from a "RESCO LINES" ARTICLE:
Misapplications and excessive application of silicone grease are major causes of connector
failures on underground molded rubber and epoxy products.
Sometimes silicone grease is applied to threaded areas (such as is on a loadbreak elbow
probe) which puts an insulator between two conductors. The grease will get caught in the
threads making full installation difficult. When the circuit heats up, the grease will flow out of the
threads and (since the probe will not be completely torqued) the resulting loose connection will
overheat and eventually fail.
Silicone grease should be used only as an aid in easier installation. All surfaces must be
thoroughly coated with a thin film so that they look shiny. A white appearance indicates
excessive application. Excessive grease tends to push back and increase assembly forces,
such as in the case of over-lubricating an elbow/bushing interface. The proper amount of
lubricant will keep the rubber components from bonding to each other.
5. OPERATION AND MAINTENANCE
a. Relubricate bushing inserts and elbow terminators every time they are operated and the system
is de-energized.
b. If a fault is closed in on with an elbow terminator, changeout the bushing insert and the elbow
terminator probe. Inspect the cable, and the elbow terminator connector and inside housing. If
there is visible carbon tracking, these should also be replaced.
6. PARTIAL VACUUM FLASHOVERS
a. PROBLEM
In the late 1980's users of 25kV and 35kV (200A) loadbreak elbows and insulating caps began
reporting incidents involving flashovers during switching operations. Study of this flashover
problem proved to be very difficult. The problem was intermittent in nature and was not easily
reproduced in the laboratory. After extensive field and laboratory study, a number of common
factors were discovered that contribute to the increased likelihood of these flashovers:
ƒ
Lightly loaded or unloaded circuits
ƒ
Higher voltages (25kV and higher)
ƒ
Cold temperatures (usually below 40° F)
ƒ
Breaking of load, not during closing (i.e., removing at elbows from, not installation of
elbows onto bushings)
ƒ
Sticking of elbows or caps during removal from bushings
Section WST04
Page 6 of 6
ELBOWS
E.C.S.
INFORMATION SECTION
Issued 08-01-08
UNDERGROUND SPLICES AND TERMINATIONS
The cause of the flashovers was determined to be the creation of a partial vacuum within the
elbow or cap. The partial vacuum causes a decrease in the dielectric strength of the air along
the interface of the probe and bushing insert. The decrease in dielectric strength is enough to
intermittently allow the energized probe to flashover to the bushing.
Flashovers occur early in the operation with an elbow or cap movement of an inch or less.
Evidence includes pitting and arcing on the upper end of the probe.
b. SOLUTION
All 25kV, 200A elbows and caps, have been changed to the "Posi-Break" design, manufactured
by Cooper Power Systems. The Posi-Break elbows and caps have an insulating sleeve over the
threaded end of the probe and an insulating layer over the conductor shield within the elbow/cap
cavity. This increases the flashover distance by 65%, which has eliminated all flashovers in
laboratory and field tests. Most of the other Wisconsin utilities utilize these elbows and caps on
their 25kV class systems.
Note: this change does not affect any 15kV system components.
c. IDENTIFICATION
A yellow/black/yellow band identifies elbows and caps as having the Posi-Break design, as well
as three-phase switching and fault close capabilities. Posi-break elbows and caps are
compatible with all bushing products (types and vintages).
(END)
Issued 06-01-07
E.C.S.
INFORMATION SECTION
UNDERGROUND SPLICES AND TERMINATIONS
Section WST05
Page 1 of 2
SPLICES
1. PRIMARY CABLE SPLICES
a. Preformed (Premolded) Splice Design
Preformed splices, apparatus connectors and other cable accessories are, in essence, an
extension of the stress cone design. In general, they consist of separable products that are
joined by mating surfaces with an interference fit. Each contain stress relief to which external
shielding, insulation and connector shielding have been added.
The understanding of these products and their designs can best be illustrated by the straight
splice (see Figure 05-1 Straight Splice).
In the preformed splice, the design is predetermined and stress control is achieved by the
principle referred to as connector shielding. The connector shield is a conductive rubber insert
that extends over the connector area and onto the cable insulation. The insert is energized at
line potential. The conducting parts are completely surrounded by an internal conductive rubber
sleeve which is smooth and symmetrical and eliminates corona caused by trapped air. In effect,
it removes electrical stress from all air in the system and confines this electrical field to the
insulating material between the two conductive portions. Thus, excellent electrical strength and
corona characteristics can be achieved. The inside diameter of the connector housing is made
slightly less than the diameter of the cable to which it is applied to effect an interference fit.
When the rubber housing is pushed into place, the elastomer is expanded and exerts a uniform
360° pressure on the cable insulation. This produces a water seal between the cable and
housing and significantly increases the electrical strength of the creep path between the
conductor and the external shield. It should be further noted that the elastomeric properties of
the rubber housing allow it to expand and contract as the cable thermal cycles, constantly
retaining 360° pressure.
Figure 05-1 Straight Splice
E.C.S.
INFORMATION SECTION
Section WST05
Page 2 of 2
SPLICES
Issued 06-01-07
UNDERGROUND SPLICES AND TERMINATIONS
b. Application
The following table lists the correct splice to use for various situations:
Table 05-1
PRIMARY CABLE SIZE
15 KV
#2 Solid
25 KV
--
SPLICE FOR GIVEN RATED CABLES(1)
15 kV to 15 kV
(2)
109318
15 kV to 25 kV
25 kV to 25 kV
--
--
(2)(4)
#2 Solid-1/0 Stranded
--
1 05574
1093 18 (2)(4)
--
--
1/0
--
105574(2)
--
--
150339(7)
104817(3)
--
--
--
150340(7)
--
103241(2)
--
107120(3)
(6)
103688
#1 Solid and
#2 Stranded
#1 Solid
3/0
--
3/0
4/0
4/0
4/0
300 kcmil
500 kcmil
--
125120(5)(8)
--
500 kcmil
500 kcmil
109393(6)
100266(2)
125120(5)
125120(5)
1000 kcmil
1000 kcmil
109306(5)
--
125121(5)
104397(6)
Source: Alliant Electrical Standards
Created: 10-94
Revised: 03-04
NOTES:
(1)
See ECS Cable Accessory and Maintenance Sections for specific accessories required.
(2)
Pre-molded splice kits complete with splice body, rejacketing tube, and connectors for
conductor and concentric neutrals.
(3)
Premolded splice kit includes splice body and conductor connector. Rejacketing sleeve (Item ID
100486) and connector for concentric neutrals must be ordered separately.
Replace connector included in kit with transition connector Item ID 106887.
Cold-shrink splice kit includes rejacketing tube and connectors for conductor and concentric
neutral.
(6)
Premolded splice kit includes splice body and conductor connector. Concentric neutral
connector must be ordered separately. These splices are for use on nonstandard unjacketed
cable installations.
(7)
Cold-shrink splice kit includes rejacketing tube and conductor transition connector. Rejacketing
tube must be installed to protect silicone rubber splice body in direct-buried applications.
(8)
Replace connector included in kit with transition connector Item ID 120325.