Instruction Manual for POC Bushings

Instruction Manual for POC Bushings
1. Scope
This instruction contains general procedures to be followed
during receiving, installation, storage and maintenance of all
PCORE POC bushings. This instruction does not cover all
contingencies that may arise during installation, operation, or
maintenance of such equipment. If you require additional
information regarding a particular installation and the
operation or maintenance of your bushing, contact PCORE.
PCORE does not assume any liability or responsibility for
any damage or failure that would result from improper
transportation, application, installation, storage, or
2. Safety
These tasks may cause safety hazards if they are not
performed properly. Those who are responsible for or
involved in the installation, maintenance, storage and
operation of the bushings must read this instruction and
understand the details before they perform the tasks.
Required procedures and instructions must be followed
when installing bushings on apparatus or building (hereafter,
any equipment or buildings on which bushings are to be
installed will be called apparatus).
All applicable safety procedures such as OSHA
requirements, regional and local safety requirements, safe
working practices and good judgment must also be used by
personnel when installing, operating and maintaining such
Some of the hazards associated with these tasks are:
Lethal electric shock
Heavy equipment
Fire or burning due to high current
High pressure
Lifting hazards
Hot oil
Hazards will be identified by the three following categories:
3.3 Insulation Materials
Standard POC bushings use electrical grade Kraft paper.
High temperature bushings use Nomex©, high temperature
gaskets and o-rings.
3.4 Oil Expansion Tanks
Three types of oil expansion tanks are used on PCORE
POC bushings: cylindrical sight glass, metal tank with
“eyeball” sight glass, metal tank with oil level gage.
3.5 Oil Level Indicators
The following are the recommended oil levels at 25°C with
the bushing in a vertical position. A bushing with either sight
glass should show half full. A magnetic oil level pointer
should indicate 250C.
Slight variation in levels due to ambient conditions can be
expected and are not an indication of oil loss or over filling.
3.6 Flanges and Flange Adapter
Flanges and flange adapters are made of aluminum. For
replacing older bushings or other manufacturers’ bushings,
PCORE offers custom-made flange adapters.
3.7 Terminals
Terminals are copper or brass. Some are silver or tin plated.
4. Cable Connections
Hazard or unsafe practice,
which MAY result in SEVERE
personal injury, death, or
property damage.
4.2 Draw Lead Connections
Some bushings are designed with a hollow conductor
through which a flexible cable or a rod can be pulled. The
cable is a part of the apparatus on which the bushing is
mounted and is not supplied with the bushing. Most drawlead terminals have a flat spade for brazing, crimp type, or
tubular brazing terminals are available.
Hazard or unsafe practice,
which MAY result in MINOR
personal injury or property
3. Bushing Components
3.1 Housings
The top and bottom insulating
electrical grade porcelain. The
vitrified and is NOT POROUS.
petticoats WILL NOT affect
3.2 Conductors
Lower current bushings have aluminum conductors and high
current bushings have copper conductors.
4.1 Bottom Connections
PCORE POC bushings have one of the following bottom
terminals: Flat spade or threaded stud. The bushings with a
flat spade can be directly connected to the apparatus. The
bushings with a threaded stud MAY need adapters to
connect to the apparatus.
WILL result in SEVERE
personal injury, death, or
property damage.
EXTREMELY sharp. Gloves
must be used when handling
broken porcelain.
housings are made of
porcelain is completely
Chips or small broken
performance. BROKEN
Page 1 of 6
4.3 Transformer and Oil Circuit Breaker
The 800 ampere draw-lead bushings in the 115 kV through
230 kV class can be bottom connected for 1200 ampere
transformer rating and can also be 1600 ampere bottom
connected for oil circuit breaker application.
interchangeability between transformer and oil circuit
breaker applications with the same basic bushing by just
changing some hardware. The current rating for transformer
application is based on the maximum oil temperature of 95o
C while that for the oil circuit breaker application is on the
maximum oil temperature of 800C.
Rev. Date 10-28-15
5. Crates
8. Handling and Installation
Three types of crates are used. Small bushings are shipped
in wire-bound crates. Large bushings are shipped in crates
with top covers held in place with reusable fasteners. The
top covers of export bushings are nailed. POC bushings in
the 15 kV through 69 kV class are shipped in the horizontal
position in crates. The top end of bushings in the115 kV
through 230 kV class are shipped at a 5° to 7° angle to keep
the paper insulation immersed totally in oil. EHV bushings
(greater than 230 kV) are shipped in the horizontal position
in crates because they are too large to keep on an angle.
8.1 Removing Bushings from Crates
88xxx Series 25 kV ~ 69 kV Bushings
(Vertical or Horizontal Mounting)
PCORE POC bushings in the 25 kV through 69 kV class can
be removed from the crate using a nylon choker around the
upper porcelain. Position the bushing vertically, and check
the oil level of the bushing before installation.
6. Receiving and Incoming
You should perform a visual inspection on the crate and the
bushing before unloading. When unloading crates, you must
take extreme care not to damage the crates or the bushings.
Do not drop the bushings. The bushings should be
unpacked in a flat, dry area
To open the wire bound crate, the twisted wires should be
straightened with pliers. The clips (on crates with reusable
clips) can be removed using a claw hammer. Remove any
nailed covers carefully to avoid damage.
Some crates contain separate boxes containing special
terminal adapters, bottom shields, oil reservoir tanks for
horizontally mounted bushings, draw-lead extensions or
other special parts. These special parts should also be
checked for damage from shipment.
Examine the porcelain for cracks or chips. Check all seals
for oil leakage. Although surface oil is removed from the
bushing after electrical testing, occasionally a gasket seal
may weep an oil film when received. To check for gasket
seal leakage, wipe the suspected joints clean and observe
for a period of 48 hours. If oil leakage is detected, contact
the factory at Le Roy. Any special parts should be checked
for damage.
Generator Step-Up (GSU) Bushings
PCORE GSU bushings must be removed from the crate
while in the horizontal position. The center of gravity is not
at the flange so a double sling must be placed between the
porcelain at the air end of the bushing and the porcelain on
the oil end of the bushing. Once the bushing is removed
from the crate and placed horizontally on a pad, eyebolt may
be attached to the top terminal to lift the bushing from
horizontal to vertical and into the apparatus.
If shipping damage is evident, you must file a claim with the
transportation carrier and notify PCORE of the claim
7. Storage
The preferred way of storing bushing is to keep them vertical
in a proper stand, which cannot be tipped over. The
preferred location is indoors, however bushings may be
stored outdoors. The crates are not made for extended
outdoor storage; inspect the crates periodically for weather
damage. It is important that the paper core be completely
submerged in oil.
Small bushings, shipped in wire-bound crates may be stored
vertically in the crates, as long as they are kept indoors.
Bushings shipped in crates at an angle can be stored on a
flat surface in the shipping crate.
The top end of larger bushings (greater than 230kV) and
low-voltage, high current bushings (25 kV through 69 kV)
should be raised about 7 degrees. The bottoms of crates for
EHV bushings must be supported in several places to
prevent crate damage.
For long term outside storage, moisture or water may gather
inside the protective plastic bag that covers the upper and
lower porcelain. Suitable protection, such as water-repellent
grease should be provided for top and bottom terminals, and
mounting hardware to protect the contact area from
corrosion. Under these conditions, the voltage tap housing
should be filled with clean, dry transformer oil. This will
prevent condensation and corrosion of the threads.
Page 2 of 6
Eyebolts must be placed in
the vertical terminals only,
lifting from the horizontal
terminal may cause damaged
to the terminal alignment.
Do not attempt to lift bushing
from the shipping crate by the
top terminal alone. The angle
of the flange in the shipping
crate may cause binding and
extreme cantilever loading on
the terminal, which may cause
damaged to the bushing.
Do not use a single sling
around the top porcelain shed
as a means of lifting. This
unbalance may cause severe
pressure against the porcelain
Rev. Date 10-28-15
115 kV ~ 800 kV Bushings
These PCORE POC bushings are provided with lifting eyes
in the flange. Because of the size and weight of the
bushings, they may require special handling. Before lifting a
bushing, remove any mounting flange bolts holding the
bushing in the crate and any other method of support which
may be used to secure the bushing.
The main lifting tackle should always be attached to the
flange lifting eyes. A second crane hook must be attached to
a double sling with a choker rope tied around the bottom of
the top porcelain.
115 kV through 230 kV class bushings
Tie two choker ropes around the top porcelain under the top
petticoat. Attach two slings to one crane hook. Pass the
other end of the sling through the eyes of each choker rope.
Attach a shackle to each of these ends. Connect the
shackles to the lifting eyes of the mounting flange 180
degrees apart.
Pass a sling through eyes of mounting flange and attach
both ends to the second crane hook. If it is not easy to pass
the sling through the eyes of the flange, you may tie a
choker rope with a sufficient strength under a petticoat
close to the bottom petticoat. Attach a sling to the second
crane hook. Attach the end of choke rope to the hook.
Lift the bushing by raising both crane hooks simultaneously
maintaining the air end of the bushing slightly above the oil
end until ready to lower the oil end of the bushing.
Under certain conditions it may be advantageous to remove
the bushing from the crate first to accommodate placement
of the choker sling or placement of shackles on the flange.
Under these conditions a sling or choker around the
porcelain is acceptable and a sling through the flange lifting
eyes would be adequate to raise the bushing and maintain a
slight angle. The bushing can be removed and placed on
adequate support, which will keep the air end raised while
adjusting the slings and cables.
When ready to lift the bushing for mounting, raise both crane
hooks simultaneously while maintaining the air end at a
slightly higher angle by lowering the crane hook attached
solely to the flange. The entire weight of the bushing will be
held by the two slings through the choker and attached to
the flange lifting eyes. The angle of orientation can be
adjusted by the raising and lowing of each crane.
345 kV through 765 kV class
From one crane hook, use two slings or a double sling
passed through a spreader bar and attach the lower end of
the slings to the mounting flange lifting eyes. The spreader
bar is not provided but such a bar must be used. The slings
should be long enough so when the bushing is vertical the
bushing will pass through and under the spreader bar.
From the second crane hook attach a sling to the choker
around the bottom of the top porcelain 90 ° degrees from the
flange lifting eyes. This crane will be used to pivot the
bushing only while the flange crane by way of the spreader
bar will support the main weight of the bushing.
Page 3 of 6
Do not place a choker sling or rope
above the top shed between the
porcelain and the metal cover. The
metal dome on PCORE bushings
consists of a spinning and may be
damaged from sling pressure.
Do not attempt to lift the
bushing by a sling on the
porcelain alone.
After the bushing is upright, check to ensure the internal
bushing oil is at the correct height in the sight glass or that
the magnetic oil level indicator is showing the proper oil level.
Rev. Date 10-28-15
8.2 Cleaning
Bushings should be kept vertically in a secure stand and you
must remove all dust, grease, oil or particles of packaging
from the bushing with clean dry cloth. Especially the lower
porcelain and flange should be wiped clean of dust or dirt to
prevent contamination of transformer oil. Before mounting
bushings to the apparatus cover, inspect and clean the
mounting surfaces of both the bushing and apparatus.
Check the inside wall of draw-lead tube especially when the
bushing has been stored outdoors a long time. If it is dirty,
remove all the dirt, dust and other foreign materials from the
8.3 Electrical Tests
PCORE recommends that power factor and capacitance
measurements be performed on all bushings before
installation. The measured values should be compared with
those on the nameplate. The nameplate values are of
special importance in asking PCORE questions about
bushings. The bushing must be kept vertically in a secure
stand for the electrical tests.
The methods of measuring power factor and capacitance
are in the user manual of your power factor measuring
device or consult IEEE Standard C57.152 IEEE Guide for
Diagnostic Field Testing of Fluid-Filled Power Transformers,
Regulators, and Reactors. Only C1 power factor and
capacitance have meanings for the 25 kV through 69 kV
class bushings. PCORE recommends against measuring C2
power factor and capacitance of this voltage class bushings
for any purpose.
After the testing has been completed, reassemble the tap
cover after coating the “0-ring” lightly with silicone grease
and tighten the cap.
8.4 Mounting Bushings
If the bushings are stored horizontally, it is important to
remove all entrapped air from the core. Place the bushing in
the vertical position and shake the oil end to force any air
bubbles out of the core area before Installation. Do not
apply voltage for at least 24 hours after installation for
the bushings rated below 230 kV and at least 48 hours
for the bushings in the 230 kV class and above
8.4.1 Mounting Angle
PCORE bushings with oil level sight glasses are designed
for safe operation in vertical position or at angles up to 70
degrees from vertical. Bushings with metal domes using
magnetic oil level gauges should not be used at angles
exceeding 30 degrees from the vertical and should be
mounted with the magnetic oil level gage facing downwards.
Bushings with metal domes using sight glasses should be
mounted with the sight glass facing sideways (see figure
PCORE bushings should not be mounted
horizontally unless the bushing is furnished with a
supplementary oil reservoir.
Do not operate the bushing
without the test tap or voltage
tap cover in place.
PCORE recommends measuring C1 and C2 power factors
and capacitances of the bushings rated 92 kV and above
prior to the installation. PCORE POC Bushings rated 92 kV
and above use a voltage tap located just above the flange
which is normally grounded in operation by means of a
ground clip in the tap cover. Unless a potential device is
used, this cover must always be installed during operation of
the bushing.
These measurements should agree with the nameplate
values within equipment tolerances and should be kept as
reference readings. When power factor and capacitance
readings are in disagreement with nameplate data beyond
reasonable tolerances, you should contact the factory at Le
Never test the bushing while
in the shipping crate.
When possible, place the
bushing in a grounded test
stand. It is important to isolate
the flange from the grounded
stand using a good insulating
material. Wood can contain
should never be used.
The readings may be taken
with the bushing installed in
the equipment provided the
top terminal connections are
not made or the terminal is
isolated from the main bus via
a PCORE Test terminal.
Page 4 of 6
8.4.2 Vertical Mounting
Lift the bushings in the same way as removing bushings
from the crates. If a flange adapter is required, install it
before moving the bushing to the mounting hole. Put the
gaskets and/or o-rings on the apparatus mounting surface
per the apparatus instruction. Move the bushing to the
mounting hole of apparatus. Tighten the bolts to the torque
specified from the apparatus manufacturer.
8.4.3 Draw-Lead Connection
Bushings designed for draw-lead applications have the
draw lead terminal, nut and pin in place. Before installation,
you must remove the top terminal, the draw lead nut, the
retaining pin and the draw lead terminal.
Braze the
apparatus cable to the draw lead terminal. Pass a wire or
pull cord through the bushing center conductor from the top
and attach it to the hole in the top end of the draw lead
terminal on the flexible cable. While lowering the bushing
into the opening in the cover, simultaneously pull the cable
up through the center conductor. Secure the draw lead
terminal into the top of the bushing by replacing the retaining
pin through the conductor and then replace the draw lead
nut. A light coating of silicone should be applied to the 0-ring
of the top terminal before replacing. Refer to the section
Bolting and Terminal Torque Settings for terminal tightness.
Rev. Date 10-28-15
Horizontal Mounting
(88xxx Series: 25 kV ~ 69 kV Bushings)
The bushings are shipped with the oil reservoir-mounting
hole plugged and with oil at the standard level for vertical
The oil volume in all bushings fluctuates
significantly with temperature. PCORE Series 88 bushings
are designed to operate with air ambient from -500C to
+400C. An oil reservoir tank mounted on the flange of an 88
series horizontally mounted bushing accommodates the oil
volume change.
are properly installed and
on the plugs.
not operate
a bushing with
the bushing oil level not visible
in the sight glass under
normal ambient conditions.
This could result in serious
damage to the bushing and/or
apparatus on which the
bushing is being mounted.
It is important to fill and install the bushing properly to
guarantee long life expectancy. Two things are extremely
important. First, all air must be out of the bushing, and
secondly, the oil level must be adjusted properly according
to the bushing oil temperature. Failure to follow these
instructions can cause bushing failure.
Before installing the bushing into the equipment (or wall),
perform the following steps while the bushing is held
A. Remove the oil filler plug in the stainless steel cover at
the top of the bushing.
B. Add oil through the fill hole in the top cover until the
bushing is completely full. Tip the bushing slightly so the air
bubble is at the fill hole in the top cover. Fill with oil until
some oil comes out of the fill hole in the top cover. Use the
extra oil supplied with the bushing, or any NON-PCB type I
or type II transformer oil. The oil must meet the minimum
requirements for new transformer oil per IEEE C57.106
(latest revision).
C. Replace the fill plug in the top cover and tighten slightly
by hand. Rock the bushing back and forth to release all
entrapped air inside the bushing into the sight glass area.
Watch the sight glass for air bubbles. Continue rocking until
no the air is being released into the sight glass. More oil may
have to be added to the bushing.
D. Loosen the oil filler plug in the top bushing cover to
bleed off the entrapped air (air bubble).
E. Add oil to the bushing until oil comes out of the fill hole
in the top cover. Be sure the fill hole in the top cover is
slightly higher than the bottom of the bushing.
F. Repeat steps B through E as necessary until the air
bubble that remains inside the sight glass is less than 1/4
inch in diameter. DO NOT STORE THE BUSHING
COMPLETELY FILLED. Any oil expansion could cause the
bushing to leak.
Install the bushing in the apparatus and perform the
following steps immediately. It is important to keep the
bushing in a horizontal position during installation.
G. Remove the oil reservoir plug from the flange and
install the oil reservoir. Be sure the O-ring is properly
installed on the reservoir.
H. Remove the oil filler plug from the oil reservoir top. IT IS
AIR. The best method is to use a dial thermometer or a
thermocouple inserted as far into the reservoir as possible.
Try to get into the flange thorough the neck of the reservoir.
minutes for the reading to stabilize.
Add oil to the reservoir until the oil level in the reservoir
is at the proper level.
THE OIL IN THE BUSHING. Use the dip stick to measure
the oil level. The top mark is for 55°C, the second is 40°C,
the middle for 25°C, the fourth for 10°C, and the bottom for 5°C oil temperature. Interpolation between marks is not
critical. If in doubt, use slightly less oil.
J. Tighten the oil fill plug in the bushing cover and install
the oil fill plug in the oil reservoir top. Make sure the 0-rings
Page 5 of 6
operation may result in severe
personal injury, death or
property damage. It is normal
for the oil level to drop below
the sight glass in some
bushings in extremely cold
conditions. Contact PCORE
Electric Company if you have
any questions.
8.4.5 Torque Specifications for Bolts
Before mounting bushings to the apparatus cover, inspect
and clean the mounting surfaces of both the bushing and
apparatus. Install the gasket or 0-ring supplied by the
apparatus manufacturer.
Secure the bushing on the
apparatus cover by tightening all the bolts uniformly in
several steps. Do not attempt to pull the bolts down to the
final setting on the first tightening. It is good practice to
allow time between the several tightening steps for the
gasket to set. Care in tightening avoids possible damage or
distortion of the mounting flange. Normally, the torque
values as listed will provide adequate compression for
Use the torque recommendations and mounting
specification of the apparatus manufacturer. Reduce
torque if gasketed per manufacturing recommendations for
material being used. Adjust torque for other metals for bolts
in flange. Values below are for SAE Grade 1 or 2.
Bolt Diameter
Thread Size
8.4.6 Bottom Terminal and Shields
If a bottom terminal and or shield is to be installed, use 40 ftlb for the ½-13 SST. bolts and 20ft-lb torque for the 3/8-16
SST. bolts. Pass the cable through the hole in the shield and
mount the bottom terminal. Then push the shield to the
bushing and mount the shield on the bushing.
8.4.7 Top Terminals
After power factor and capacitance tests are completed for
the apparatus, connect the top terminal for energization.
Rev. Date 10-28-15
9. Partial Discharge Tests
PCORE does NOT add a pressurized gas blanket over the
top of the oil in the bushings. It is possible to encounter
some partial discharges in the sight glass during overvoltage
tests. The partial discharges are a result of a partial vacuum
formed in the gas space above the oil. The condition occurs
most often after transformer heat-run tests. It can be
eliminated by venting the gas space to atmospheric pressure.
When the bushing is hot, do
NOT remove oil fill plug.
10. Energization
During initial energization, you should monitor oil level
changes. If oil level changes excessively, contact the factory
in Le Roy.
12. Re-shipping or Returning
To ship the bushing to another site, you may re-use the
original crate. Inspect the crate for damage and repair
before using.
Bushings with damaged porcelain or sight glasses pose
a significant danger. The entire assembly is under
compressive load, releasing that load suddenly may
cause the bushing to explode. Wrap broken porcelain or
glasses with duct tape and blankets (Burlap works well).
It is recommended that bushings be returned to the factory
for all significant repairs. Inquiries concerning repairs should
be addressed to the factory at Le Roy. You MUST obtain a
Return Authorization (RO) number before shipping bushings
or bushing attachments to PCORE. The handling of all
requests will be expedited if the factory is furnished the
catalog number and the serial number which are on the
nameplate. The catalog number identifies the bushing rating.
The first two digits of the serial number are the last two digits
of the manufacturing year.
11. Maintenance
Little maintenance is required other than periodically
checking the oil level as indicated in the sight glass or the
magnetic oil level gage. Unless a bushing is damaged, the
oil level should remain within the sight glass or indicate
normal with the oil level gage, fluctuating slightly with
thermal and ambient conditions.
Although we discourage the breaking of the seal of the oil-fill
plug in the bushing reservoir; if the oil level over an observed
period of time remains low and ambient conditions are
normal, oil may be added. However, contact the factory in Le
Roy first.
Removal of oil filler plug should be done only in a dry
atmosphere. Provide oil that meets the IEEE C57. 106
standard for new transformer oil. If there is mechanical
damage to the bushing which results in loss of oil, or the oil
level in the bushing is still indicating low after the addition of
oil the bushing should be taken out of service.
Do not attempt field repairs.
A bushing experiencing a core
problem may have a high
pressure and/or hot oil inside.
Do not remove oil fill plug.
pressures. A bushing with a
shattered oil sight glass must
be wrapped with burlap and
duct tape before the bushing
is removed from installation.
Never operate or test a
bushing with a low internal oil
level. Under these conditions,
operation may result in severe
personal injury, death or
property damage
Bushings exposed to salt spray, cements dust, and other
abnormal contamination deposits are subject to a special
hazard and must be cleaned regularly to prevent flashover
and corrosion of metal parts. The sight glass should also be
cleaned regularly. We endorse and recommend the
measurement of power factor and capacitance at the time of
installation and repeating the measurement regularly. These
values should be used as a base to compare the TRENDS
of future measurements. Field measurements of power
factor and capacitance may differ from measurements made
under the controlled conditions in the factory. Contact the
factory if you encounter any of the following:
A. Measurement of power factor increases to 1.5 times the
original installation value.
B. Measurement of capacitance increases by 10 percent
over the original installation value.
Page 6 of 6
Rev. Date 10-28-15