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E.C.S.
INFORMATION SECTION
OVERVOLTAGE APPLICATION GUIDELINES
Section WOV00
Page 1 of 1
INDEX
S E C T I O N W O V 0 1 : O V E R V O L T A G E ............................................................................. Page 1
G E N E R A L .................................................................................... Page 1
V O L T A G E R A T I N G S ................................................................ Page 3
DISTRIBUTION DELIVERY SYSTEM ARRESTER
A P P L I C A T I O N S ......................................................................... Page 5
ARRESTER MOUNTING LOCATIONS ON
O V E R H E A D L I N E S .................................................................. Page 7
I N S T A L L A T I O N O F A R R E S T E R S O N R E C L O S E R S .... Page 8
INSTALLATION OF ARRESTERS ON
R E G U L A T O R S .............................................................................. Page 12
INSTALLATION OF ARRESTERS ON GROUP
O P E R A T E D L O A D B R E A K S W I T C H E S .............................. Page 15
INSTALLATION OF ARRESTERS ON
S W I T C H G E A R ........................................................................... Page 15
E.C.S.
INFORMATION SECTION
Issued 06-01-07
OVERVOLTAGE APPLICATION GUIDELINES
Section WOV01
Page 1 of 15
OVER VOLTAGE
1. GENERAL
a. Causes of Overvoltage
Problems associated with overvoltage are caused by lightning, as well as delivery system
switching operations.
b. Consequences of Overvoltage
Lightning causes the most overvoltage damage to distribution delivery systems. When lightning
strikes on or near the distribution system, equipment may fail and overhead conductors may
burn down, fuses may experience nuisance operations, poles may be splintered or other system
problems may result. Damage to utility facilities caused by lightning may increase the number
and duration of outages, which may lead to customer dissatisfaction, as well as increased
operations and maintenance costs.
Energized utility equipment has sufficient insulation levels to withstand momentary system
overvoltages up to the basic lightning impulse insulation level or BIL. BIL is the maximum level
of impulse voltage the equipment can tolerate before flashing over.
Industry standard equipment BIL ratings are as follows:
Distribution System Voltage Class
Equipment BIL Rating
5 kV
60 kV
15 kV
95 kV
25 kV
125 kV
35 kV
150 kV
c. Arrester Operation
Lightning protection of delivery system facilities is provided by shield wires, additional insulation,
system grounding, combined BIL of equipment and lightning arresters.
Arresters are designed to limit transient surge voltages to a level below the flashover or BIL
rating of the facilities. Above a designed voltage limit, an arrester will conduct lightning and
switching current to ground. These devices are designed to conduct high currents for short
durations and require no maintenance, but will fail if subjected to excessive energy levels during
delivery system overvoltage situations.
Due to the variation of lightning current magnitude, arresters will not survive all direct lightning
strikes. When an arrester fails, the disconnector (isolator) should visibly drop open from the
bottom of the arrester, effectively creating an open circuit and isolating the arrester from the rest
of the system.
Both top and bottom arrester terminals have a copper conductor range of #6 solid - 1/0
stranded.
d. Types of Arresters
There are two basic types of surge arresters used to protect distribution delivery systems, metal
oxide (MOV) and silicon carbide (SiC). Each type contains series elements that have non-linear
voltage characteristics which permit the conduction of current during a delivery system
overvoltage condition.
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OVER VOLTAGE
Issued 06-01-07
OVERVOLTAGE APPLICATION GUIDELINES
SiC arresters consist of several silicon carbide blocks in series and also requires a series gap to
prevent power frequency voltages from appearing across the SiC blocks. Following sparkover,
the SiC blocks dissipate energy and limit the overvoltage after the sparkover occurs. With SiC
arresters, power-follow current will occur until the next “zero” crossing of the current waveshape.
Silicon carbide arresters are no longer made, although many still exist on our systems.
Metal Oxide Varistors (MOV) have non-linear voltage characteristics. Based on their non-linear
voltage characteristics, MOV’s do not require a gap for proper operation. Most MOV arresters
are gapless. However, some MOV arrester designs do offer a gapped version. The gapped
MOV reduces the voltage stress on the arrester which makes the arrester less susceptible to
temporary overvoltage failures. MOV blocks can withstand rated power frequency voltage better
than the SiC arresters. The MOV will immediately go into conduction, start dissipating energy
and limit overvoltage as it sees a surge. MOV arresters typically provide better overvoltage
protection than SiC arresters.
Arresters are enclosed with either a porcelain or a polymer housing. Polymer housings do not
fragment as catastrophically as porcelain upon arrester failure, and therefore are safer.
e. Arrester Installation Considerations
The two most important components impacting the effectiveness of an arrester are the lead
lengths and the ground resistance.
1) Lead lengths should be kept as short as possible on both the line side and ground side of
the arrester to maximize the margin of protection provided by the arrester. Margin of
protection is the difference between the BIL (Basic Insulation Level) of the equipment being
protected, and the discharge voltage across the arrester and the arrester lead. Arrester lead
is the combined length of energized line and ground wire in series with the arrester and in
parallel with the device being protected. In other words, arrester lead lengths include only
those wires which carry surge current through the arrester AND are connected across the
device being protected. Since the arrester discharge voltages are fixed, to minimize the
voltage across the device being protected, the arrester lead length should be kept as short
as possible. For the best protection to eliminate both line and ground lead lengths, and carry
the line and ground connections to the arrester terminals first and then to the terminals of
the device being protected.
2) Excessive ground resistance (greater than 40 ohms) may lead to flashover situations
because of the excessive voltage difference between the grounding conductor and phase
conductors. Therefore, a good ground is required for proper arrester operation.
To avoid breaking the arrester bracket during installation through a bending moment in excess
of the bracket strength, brace the top of the arrester while tightening the top connection. Also,
brace the bottom of the arrester while tightening the bottom connection.
A nylon-retaining washer suspends the U-washer to aid in ease of installation. The wire should
be run straight through the terminal, it does not need to be wrapped around the terminal.
f.
Arrester Classifications
There are five classes of arresters: station, intermediate, distribution (heavy duty and normal
duty), riser pole and secondary.
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INFORMATION SECTION
OVERVOLTAGE APPLICATION GUIDELINES
Section WOV01
Page 3 of 15
OVER VOLTAGE
Each class has different requirements and are designed to meet different industry standard
tests. Arrester costs are directly related to the amount of protection provided. For most
overhead and underground installations, distribution class arresters are used. For underground
cable risers or dips, riser pole class arresters are used. In substations, intermediate and station
class arresters protect transformers, reclosers, underground cable exits and other equipment.
2. VOLTAGE RATINGS
a. Safety Concerns
It is extremely important for safety and system protection reasons that the correct voltage rated
arresters be installed. For these reasons, it is recommended that the equipment nameplates be
checked for the appropriate voltage rating before voltage-sensitive equipment is installed.
b. Application Guidelines
1) Arresters should be selected from Table 01-1 for the proper system voltage and MCOV
rating.
2) The arrester must have a voltage rating greater than the line-to-ground system operating
voltage.
3) The arrester voltage rating should be less than the voltage rating of the equipment being
protected.
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OVER VOLTAGE
Issued 06-01-07
OVERVOLTAGE APPLICATION GUIDELINES
Table 01-1 Alliant Arrester Table
ARRESTER TABLE
Application
MCOV
Rating
Duty
Rating
Item ID
4,160 V Wye
Floated Wye-Delta Banks ***
Overhead Distribution - Heavy Duty
10.2 kV
12 kV
120982
8.4 kV
10 kV
105929
Elbow 10 kV
8.4 kV
10 kV
123024
Parking Stand with 15 kVCable no mtg bkt included
8.4 kV
10 kV
103584
Riser Pole with 15 kV Cable no mtg bkt included
8.4 kV
10 kV
107186
Riser Poles with 5 kV Cable - Distribution Class
2.55 kV
3 kV
100805
12.47 kV, 13.2 kV, & 13.8 kV Grounded Wye
Floated Wye-Delta Banks
Overhead Disribution - Heavy Duty
10.2 kV
12 kV
120982
8.4 kV
10 kV
105929
Elbow 10 kV
8.4 kV
10 kV
123024
Elbow 10 kV with 25 kV Interface
8.4 kV
10 kV
107668
Parking Stand with 15 kV Cable no mtg bkt included
8.4 kV
10 kV
103584
Riser Pole Class no mtg bkt included
Switchgear no mtg bkt included
8.4 kV
10 kV
107186
8.4 kV
10 kV
100313
Substation - Intermediate Class **
8.4 kV
10 kV
108748
13.8 kV Impedance Grounded Delta & 14.4 kV Wye
Overhead Distribution - Heavy Duty
Riser pole - Distribution Heavy Duty
10.2 kV
12 kV
120982 *
10.2 kV
12 kV
120982*
Elbow 18 kV with 15 kV Interface
15.3 kV
18 kV
122991
Substation - Intermediate Class **
15.3 kV‘
18 kV
105743
14.4 kV Delta & 24.9 kV Grounded Wye
Floated Wye-Delta Banks
Overhead Distribution - Heavy Duty
19.5kV
24kV
125035
15.3 kV
18 kV
101668
Elbow 18 kV with 15 kV Interface
15.3 kV
18 kV
122991
Elbow 18 kV with 25 kV Interface
15.3 kV
18 kV
125311
Riser Pole Class no mtg bkt included
15.3 kV
18 kV
122877
Substation - Intermediate Class **
15.3 kV
18 kV
105743
*Some Items ID are listed for cross reference only.
**Intermediate class arresters are installed in substations only to protect reclosers, breakers, and
underground substation circuit exit.
***12kV arrester is used on 4,160V system to maintain consistency of a gapped MOV arrester on all
floated wye-delta banks. (The 12kV gapped arrester has the same, or better, charateristics as the 10kV
arrester.)
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INFORMATION SECTION
OVERVOLTAGE APPLICATION GUIDELINES
Section WOV01
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OVER VOLTAGE
3. DISTRIBUTION DELIVERY SYSTEM ARRESTER APPLICATIONS
Arresters are installed at the following locations to protect distribution equipment from overvoltage:
a. Overhead Normally Open (N.O.) Points
Lightning arresters shall be installed at all normal open points on the overhead distribution
system. The purpose of this recommendation is to minimize the damage that can be caused by
the voltage doubling effect which occurs after the lightning waveform reflects back at these
normal open points. Arresters should be selected from Table 01-1 for the proper system
voltage, and be the same arresters that are applied for general line protection.
b. Underground Normally Open (N.O.) Points and Padmount Transformers
Lightning arresters shall be installed at all normal open points on a looped underground
distribution system, as well as at the first padmounted device on either side of the normal open
points. This recommendation shall be followed whether the normal open point is pad-mounted
switchgear, an elbow cabinet, or a transformer with an open switch or stand-offs. Lightning
arresters shall be installed at the padmounted device located at the end of a radial underground
tap and the first padmounted device upline from the last device on the radial underground tap.
This recommendation shall be followed whether the end of the radial underground tap is
padmounted switchgear, an elbow cabinet, or a transformer. The purpose of these
recommendations is to minimize the damage that can be caused by the voltage doubling effect
which occurs after the lightning waveform reflects back at these normally open points on the
system. Studies have shown that the addition of a second arrester, located up-line from the
normal open point or end-of-line point, can significantly increase the protection of the
underground system. Arresters should be selected from Table 01-1 for the proper system
voltage and the proper device that the arresters will be applied to.
c. Capacitor Banks
For capacitor bank protection, the line jumpers feeding the capacitor banks shall be routed to
the arresters and then to the cutouts. Arresters and cutouts are to be located on a bracket that
is dropped 33 inches below the lowest phase conductor as illustrated in the Capacitor
Assemblies, Section B15A.
d. Gang Operated Loadbreak Switches (GOLB)
Arresters are located on either side of a gang operated switch, whether the switch is operated
normally open or normally closed. If installation of arresters at the GOLB is not practical due to
the construction of the switch or configuration of equipment on the pole, then arresters will be
installed at the closest structure located either direction of the GOLB.
e. Reclosers and Regulators
Arresters should be mounted on the regulator or recloser tank using the provided tapped inserts
on the load and source side of regulators or the necessary hardware for recloser tank mounting
on both the source and load sides for each phase. By mounting the arresters at the tank,
arrester lead lengths are minimized, increasing the overvoltage protective margins.
f.
Overhead Transformers
As with reclosers and regulators, arrester lead lengths can be minimized by installing the
arresters on the transformer tank. However, for low current fuse links, arresters placed on the
load side of the fuse can increase the number of nuisance fuse operations (NFO’s) for overhead
distribution transformers. An NFO is defined as a fuse operation at a distribution transformer
bank where no transformer damage is evident. After replacing the fuse, the transformer
operates normally.
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OVER VOLTAGE
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OVER VOLTAGE APPLICATION GUIDELINES
Most NFO’s are believed to occur from lightning surge current conducted by the arrester, as well
as any current conducted by the transformer. These currents may heat the fuse element to the
point of melting. Studies indicate that where arresters are placed on the load side of fuse links,
NFO rates decline as the fuse size is increased.
Where the arrester is located on the source side of the fuse, most of the lightning current will
pass to ground through the arrester. The fuse link will only see the transformer current during a
lightning surge.
The following takes into consideration NFO’s, arrester lead length and industry standard
transformer overvoltage protection margins. For transformers protected by 15T, 20K, or 20
Standard speed fuse links or greater, the arrester will be tank mounted. For transformers
protected by fuse links less than 15T, 20K, or 20 standard speed, arresters should be mounted
remotely on the arrester/cutout bracket or crossarm.
g. Overhead Distribution Lines
Arrester placement studies have shown marginal improvement between arresters located every
other pole versus every third pole. Although these same studies showed that the most effective
use of arresters is on every pole. The installation of arresters, on every phase at every third
pole, is the most cost effective application.
h. Underbuild Circuits
Due to the difference in BIL of transmission and distribution facilities, when lightning strikes a
transmission structure with distribution underbuild, the distribution phase located adjacent to the
pole is most likely to flashover. Due to the high probability of flashover to the distribution circuit
and the longer span lengths of most transmission lines, the recommended practice is to install
an arrester on only the distribution phase conductor nearest the pole at every
transmission structure. At locations where poor grounding is known to exist (40 ohms or
greater), arresters should be placed on all distribution phase conductors.
i.
Underground Cable Riser or Dip Locations, Single and Three Phase
Riser pole class arresters shall be installed at all underground riser/dip poles where the primary
underground distribution system is connected to the primary overhead distribution system.
These arresters will reduce the amount of voltage seen on the underground system when a
voltage surge is present on the overhead system. Riser pole class arresters should be mounted
using the single or three-phase arrester/terminator bracket as specified in the Riser Pole
Assemblies (Section G85A). Refer to Table 01-1 to select the proper riser pole class arresters
for the system voltage that they will be applied to.
j.
Placement of Arresters With Fuse Links
Standard overhead distribution practices have been to place the arrester on the source side of
the fuse link (cutout), except at riser/dip poles where the arrester is mounted next to the cable
terminator. Recent studies support the conclusion that when an arrester is located on the load
side of a fuse link, smaller fuse links are much more susceptible to nuisance fuse operations.
When the arrester is located on the load side of the fuse, the current flowing through the
arrester as it operates also flows through the fuse link and may cause smaller fuses to operate.
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OVERVOLTAGE APPLICATION GUIDELINES
Section WOV01
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OVER VOLTAGE
At locations where the fuse link is located remote from the transformer (such as a farm service
tapped at the road with the transformer and arrester one or more spans away), the
recommended practice is to install an additional arrester to protect the fuse link. This requires
the installation of two arresters, one at the transformer and one ahead of the fuse link. This will
also require an additional pole ground to be installed (for the arrester) at the pole with the
arrester-fuse link combination. The following diagram depicts this situation:
Figure 01-1 Arrester Installed at Fuse Link
This practice applies mainly to transformer fuses and tap fuses less than 15T, 20K, or 20
Standard speed. Since most sectionalizing fuses are larger, they are less susceptible to the
surge currents that damage the link. Thus, it is not necessary to place arresters at sectionalizing
fuses.
4. ARRESTER MOUNTING LOCATIONS ON OVERHEAD LINES
For an extra margin of safety and system reliability, grounded conductors should be kept safely
below the phase conductors. Therefore, it is recommended that arresters always be mounted 33
inches below the lowest phase conductor. Following are four primary structure categories
describing recommended and optional locations for cutouts and arresters.
a. Single-Phase Structures
Unless the arrester is tank mounted, the cutout and arrester should be mounted on a T-bracket
below the crossarm mounting position on all single-phase structures, regardless of specific
operating voltage. The T-bracket is necessary to increase the distance the arrester and the
bottom of the cutout (since it is mounted on an angle) are from the pole to minimize the chance
of flashovers.
b. Three-Phase Equipment Structures
Unless arresters are tank mounted, cutouts and arresters must always be mounted on a sixposition bracket below the crossarm on structures carrying three-phase equipment regardless of
the operating voltage.
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OVER VOLTAGE
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OVER VOLTAGE APPLICATION GUIDELINES
c. Three-Phase Structures with Single-Phase Equipment
1) Recommendation
Unless the arresters are tank mounted, it is recommended that cutouts and arresters be
installed below the crossarm on a bracket, regardless of the voltage. This will allow easier,
safer operation and replacement of cutouts and arresters, (i.e., being out of reaching
distance by hand of the primary line). The ECS assemblies show this as the standard
practice.
2) Option
While the line is operating at 4.16 kV – 13.8 kV, cutouts and arresters may be placed on the
crossarm. However, if the line voltage is converted to 25 kV, the cutouts and arresters
(unless arresters are tank mounted) must be relocated on a bracket below the crossarm.
Keep in mind, the 108-inch spacing (urban) and 90-inch spacing (rural) from the top of the
pole to the neutral must be maintained to allow for this relocation.
d. Three-Phase Structures with Fused Taps
An arrester should be installed below the crossarm on the arrester/cutout bracket if the tap fuse
size is less than a 15T, 20K or 20 Standard.
e. First Three-Phase Structure Outside of Substation
For overhead distribution substation feeder exits, three arresters should be installed on the first
structure outside the substation. These arresters should be the same arresters that are applied
for general distribution line protection.
5. INSTALLATION OF ARRESTERS ON RECLOSERS
All new distribution line recloser installations should include the use of arresters to provide surge
protection. All installations should include two arresters per phase, one each for the load and
source side. Arresters should be selected from Table 01-1 for the proper system voltage, and be
the same arresters that are applied for general line protection. It is important that the arresters be
located as described below to provide maximum surge protection.
a. Single-Phase Reclosers
1) Option 1
On single-phase reclosers, two arresters should be mounted to the recloser by removing two
3/8 inch tank cover bolts, installing the flat strap of a crossarm bracket (Item ID #122633) to
these bolts, and attaching the arresters to the other end of the bracket strap using 2 inch x
3/8 inch bolts (Item ID #103390). This strap has 3/8 inch holes and the arrester mounting
bracket has a 1/2 inch hole, therefore, two 3/8 inch washers (Item ID #122121) are also
required. For Option 1 to work on reclosers with 1/2-inch diameter tank cover bolts, the hole
on one end of the flat strap must be drilled out since they are 7/16-inch diameter holes.
2) Option 2
An alternate way of mounting the arresters is to use two of the "L-shaped" parts of the
crossarm brackets and bolt them together using two 1-1/2 inch x 3/8 inch bolts (Item ID
#106867) and two 3/8 inch washers per bolt.
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INFORMATION SECTION
OVERVOLTAGE APPLICATION GUIDELINES
Section WOV01
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OVER VOLTAGE
3) General
The ECS assemblies reflect the first option. This application refers to one single-phase
recloser and three cluster-mounted single-phase reclosers, as well (See Figure 01-2). The
arrester line lead should connect to the recloser jumper just above the recloser bushing. The
ground lead of the arresters should be connected to the recloser tank ground and ground
rod using one continuous #4 pole ground wire.
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OVER VOLTAGE
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OVERVOLTAGE APPLICATION GUIDELINES
Figure 01-2
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Section WOV01
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OVER VOLTAGE
b. Three-Phase Reclosers
For three-phase reclosers, three arresters should be mounted at the recloser away from the
pole, using the arrester bracket (Item I.D. #103015) which attaches directly to the recloser rack
[see Figure 01-3 and Figure 01-4]. The arrester line leads should be connected to the recloser
jumpers just above the recloser bushing. The ground lead from the arresters should be
connected to the recloser tank ground using one continuous #4 copper jumper wire. This
installation should allow adequate climbing space while providing lightning protection for the
recloser at the same time. To protect the other side of the recloser, another set of three
arresters should be mounted one span away on an adjacent pole using the 25 kV three-phase
arrester/terminator bracket (Item I.D. #107863). Install a pole ground on this adjacent pole
unless one already exists. One of these two sets of arresters should be connected to the source
side and the other set to the load side of the recloser.
Figure 01-3
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Figure 01-4
6. INSTALLATION OF ARRESTERS ON REGULATORS
All new distribution line regulator installations should include the use of arresters to provide
equipment surge protection. All installations should include two arresters per phase, one each
mounted on the load and source side. Arresters should be selected from Table 01-1 for the proper
system voltage, and be the same arresters that are applied for general line protection. It is
important that the arresters be located as described below to provide maximum surge protection.
a. Single-Phase Regulators
On single-phase regulators, two arresters should be mounted to the regulator using the
provided arrester mounting bosses as shown in “Figure 01-6 - Location of Arrester Mounting
Bosses” on page 13.
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OVERVOLTAGE APPLICATION GUIDELINES
Figure 01-5 - Regulator Arrester Bracket 04-2043
Section WOV01
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OVER VOLTAGE
Figure 01-6 - Location of Arrester Mounting Bosses
Two arrester brackets (Item I.D. #108223) with bolts should be used to attach the arresters
directly to the regulator tank. The arrester line leads should be connected to the regulator
jumpers just above the regulator bushing. The ground lead from the arresters should be
connected to the regulator tank ground using one continuous #4 copper jumper wire. This
installation should allow adequate climbing space while also providing lightning protection for
the regulator.
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OVERVOLTAGE APPLICATION GUIDELINES
Figure 01-7 - Location of Arresters on Line Regulators
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Section WOV01
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OVER VOLTAGE
7. INSTALLATION OF ARRESTERS ON GROUP OPERATED LOADBREAK SWITCHES
Lightning protection shall be provided for all group operated load break switches.
Insulation of the switch operating handle from the switch prohibits installation of lightening arrester
on the switch structure. Consequently, lightning arresters shall be mounted on the first (adjacent)
pole on each side of every group operated switch.
Lightning arresters maybe installed on the switch structure when the following conditions have been
satisfied.
1) The insulator in the switch operating rod is not present, and
2) The switch handle has been grounded to the system neutral and a ground grid has been
provided to mitigate potentially lethal step potential.
A lightning arrester bracket is available for mounting arresters directly to the switch assembly.
Refer to Information Section WOD09 for mounting instructions.
8. INSTALLATION OF ARRESTERS ON SWITCHGEAR
Six arresters should be installed at each switchgear where a normally open exists on the
underground primary cable system. Three arresters should be installed in the normally open
compartment. Three arresters should be installed in any of the remaining switch compartments.
a. Livefront Padmounted Switchgear
S&C PMH 15 kV padmounted switchgear will come equipped (See Figure 01-8 - Location of
Arresters in Switch compartment S&C 15 kV Padmounted Switchgear) with an arrester
mounting bracket installed in every gang-operated switch compartment. The mounting bracket
is designed to hold three switchgear type arresters. Please refer to Table 01-1 for the correct
Item ID numbers. If a normally open is established in an existing switchgear, mounting brackets
should be installed in the normally open compartment and any of the remaining switch
compartments. The mounting bracket will be available for existing switchgear where arresters
are needed.
Figure 01-8 - Location of Arresters in Switch compartment S&C PMH Padmounted Switchgear
b. Deadfront Padmounted Switchgear
In deadfront switchgear, elbow arresters should be installed on the 600 Amp cable elbows using
the same guidelines as above, six arresters per switchgear installation.
(END)