Document 2.4.54, Revision 0
July 2006
Instructions
Installation, Operation, and Maintenance
of Substation Transformers Through 10,000 KVA
Howard Industries
Substation Transformer Division
Document 2.4.54 Revision 0
July 2006
Small Power Substation Transformers
! IMPORTANT SAFETY INFORMATION !
Read these instructions carefully before proceeding with installation, operation, or maintenance of this equipment.
Small power transformers contain extremely hazardous voltages. To prevent death, serious personal injury, or property
damage, all information in these instructions should be read and observed. Safe use of this equipment is dependent
on proper installation, operation, and maintenance procedures.
Certain information in this manual is marked with the words DANGER, WARNING, or CAUTION. DANGER indicates an
imminently hazardous situation which, if not avoided, will result in death, serious personal injury, and property damage.
WARNING indicates a potentially hazardous situation which, if not avoided, could result in death, serious personal
injury, and property damage. CAUTION indicates a potentially hazardous situation which, if not avoided, may result in
minor or moderate personal injury, and property damage.
Personnel should not attempt to service this equipment until it has been completely de-energized and all high-voltage
and low-voltage bushing terminals have been properly grounded.
Only qualified personnel should install, maintain, and operate this equipment. Qualified personnel are those who are
trained in the installation, maintenance, and operation of high-voltage equipment, trained in the proper use of protective
equipment (such as rubber gloves, safety glasses, protective clothing
aid procedures.
, hard hats, etc.), and trained in appropriate first
IMPORTANT INFORMATION ABOUT THESE INSTRUCTIONS
The instructions contained herein are intended to be a general guide for the installation and operation of Howard
Industries small power transformers when used in typical applications and operated in normal environments.
Although efforts have been made to ensure accuracy and completeness, these instructions do not address every
conceivable application or circumstance that might be encountered. Features presented herein may not be present
in all transformer designs. Standard and optional features are subject to change without notice.
Howard Industries makes no representation or warranty with respect to and assumes no responsibility for the
completeness, accuracy, sufficiency, or usefulness of these instructions. Questions regarding installation, operation,
and maintenance (particularly when encountering unusual or special circumstances not sufficiently covered by
these instructions) should be directed to the Howard Industries Substation Transformer Division.
2
TABLE OF CONTENTS
IMPORTANT SAFETY INFORMATION .................................................................................................................................................................. 2
IMPORTANT INFORMATION ABOUT THESE INSTRUCTIONS ............................................................................................................................. 2
RECEIVING INSPECTION ....................................................................................................................................................................................4
Drawings and Documents ........................................................................................................................................................................... 4
External Inspection ......................................................................................................................................................................................
Tank Pressure ..............................................................................................................................................................................................4
Internal Inspection ......................................................................................................................................................................................4
HANDLING .......................................................................................................................................................................................................... 5
Lifting ........................................................................................................................................................................................................... 5
Jacking, Skidding, and Rolling ....................................................................................................................................................................
STORAGE ............................................................................................................................................................................................................. 6
Transformer Storage .................................................................................................................................................................................. 6
Extended Storage .......................................................................................................................................................................................
INSTALLATION ..................................................................................................................................................................................................... 7
Location and Mounting ...............................................................................................................................................................................
Opening Transformer Tank .......................................................................................................................................................................... 7
Installation of Detachable Radiators .........................................................................................................................................................8
Filling Installed Radiators with Fluid ..........................................................................................................................................................
Installation of Surge Arresters .................................................................................................................................................................... 9
Installation of Air Terminal Chamber and 15kV or 5kV Switchgear Adapters .........................................................................................
Pre-energization Tests and Checklist .........................................................................................................................................................9
COMPONENTS AND ACCESSORIES .................................................................................................................................................................11
Transformer Nameplate ............................................................................................................................................................................ 11
Control Cabinet ..........................................................................................................................................................................................11
Alarm Switch Ratings ................................................................................................................................................................................11
Current Transformers ................................................................................................................................................................................ 11
Pressure/Vacuum Gauge .......................................................................................................................................................................... 11
Automatic Pressure Relief Device ............................................................................................................................................................11
Fluid Level Gauge ......................................................................................................................................................................................
Fluid Temperature Gauge .........................................................................................................................................................................
Winding Temperature Gauge ....................................................................................................................................................................12
Thermal Overload Relay ............................................................................................................................................................................12
Rapid Pressure Rise Relay ........................................................................................................................................................................
Transformer Cooling Fans .........................................................................................................................................................................12
De-energized Tap Changer ........................................................................................................................................................................13
Dual-Voltage or Delta/Wye Switch ...........................................................................................................................................................13
High-Voltage Bushings .............................................................................................................................................................................. 14
Low-Voltage Bushings ............................................................................................................................................................................... 14
Surge Arresters ..........................................................................................................................................................................................14
Radiators .................................................................................................................................................................................................... 14
MAINTENANCE .................................................................................................................................................................................................15
Periodic Tests and Inspections .................................................................................................................................................................15
Sampling of Insulation Fluid .................................................................................................................................................................... 15
Gaskets ...................................................................................................................................................................................................... 16
Additional Maintenance Instructions ....................................................................................................................................................... 16
Repair Parts ............................................................................................................................................................................................... 16
Warranty Claims ........................................................................................................................................................................................16
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12
12
4
5
6
7
8
9
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Document 2.4.54 Revision 0
July 2006
Small Power Substation Transformers
RECEIVING INSPECTION
These instructions apply to substation transformers
manufactured by Howard Industries. It is important
to read the safety information on page 2 before
attempting any installation, operation, or maintenance
activities.
Although all transformers, components, and
accessories are carefully inspected and tested prior
to shipment, a thorough receiving inspection should
be conducted to detect any damage or loss that
might have occurred during shipment. The receiving
inspection should be completed upon receipt and
before unloading from the truck. Note any damage or
discrepancies on the bill of lading, file a claim with the
carrier, and notify the Howard Substation Transformer
Division prior to unloading the transformer.
Drawings and Documents
Locate all shipping papers, packing lists, outline
drawings, and other pertinent information. Use these
documents and this manual during the inspection.
The transformer outline drawing indicates the locations
of nameplates and warning labels, and provides
physical dimensions and weights. The nameplate
provides electrical characteristics, winding connections,
and weights. The wiring diagram provides details of
control, fan and alarm wiring.
DO NOT REMOVE OR OBSCURE ANY WARNING LABELS
OR NAMEPLATES.
Tank Pressure
The tank vacuum/pressure gauge may indicate
positive or negative when the transformer is
received, depending on the relative fluid and ambient
temperatures. This indicates that the transformer
is sealed effectively. If the vacuum/pressure gauge
reads zero, this may indicate the possibility of a tank
leak; although, a zero reading can occur occasionally
with changing internal and external temperatures.
In the case of a zero reading, the tank should be
pressure tested according to the instructions on page
9 (Pre-energization Tests and Checklist). Report
any suspected tank leaks to the Howard Substation
Transformer Division.
Internal Inspection
An internal inspection of the transformer tank is
rarely necessary and is required only when there are
indications that the transformer has received severe
impact damage during transit. If an internal inspection
is necessary, follow the instructions on page 7 for
opening the transformer tank. Contact the Howard
Substation Transformer Division before proceeding with
any internal inspection.
External Inspection
The following external inspections should be made at a
minimum.
1. Verify that all equipment, accessories, and
components listed on the bill of lading are
present.
2. Ensure there are no signs of external damage.
3. Verify the paint finish has not been damaged.
4. Ensure that fittings, conduit, wiring, and other
attachments are tight and undamaged.
5. Check for evidence of fluid leakage on the
tank, valves, or cooling assemblies.
6. Check for damage to the bushings.
7. Check for damage to the shipping crates,
packages, or other materials shipped
separately from the transformer.
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Small Power Substation Transformers
HANDLING
Lifting
Lifting hooks are provided near the top of the
transformer tank for lifting. All four lifting hooks must
be used simultaneously. The transformer must not be
lifted from any points other than the provided lifting
hooks. It is recommended that spreader bars be used
to keep the lifting cables nearly vertical, reducing the
likelihood of tank deformation or damage to painted
surfaces. Transformers should be lifted in an upright
position, allowing no more than 15 degrees of tilt
from vertical. Lifting cables shall be no more than 20
degrees from vertical.
Document 2.4.54 Revision 0
July 2006
Jacking, Skidding, and Rolling
Jacking pads are provided at all four corners of the
transformer base for use in jacking. Do not use
cooling fins or pipes, valves, or sheet metal surfaces
for jacking. Jacking must be done from two adjacent
corners simultaneously to prevent warping of the tank
bottom. When rolling, use an adequate number of
rollers to distribute the transformer’s weight evenly.
Refer to the transformer outline drawing for the location
of jacking pads on the transformer tank.
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July 2006
Small Power Substation Transformers
STORAGE
Transformer Storage
Transformers can be stored if properly prepared. It is
recommended that stored transformers be completely
assembled. Prior to storage, transformers should be
pressure tested according to the instructions on page 9
(Pre-energization Tests and Checklist). The gas space
above the insulating fluid should be pressurized with
dry nitrogen to a pressure between two and three PSIG.
This will prevent a negative internal pressure which
might draw moisture into the tank. Transformers not
designed for outdoor use must be stored indoors. If
the transformer is not completely assembled, separate
components and accessories should be stored in a
clean dry area in their original shipping containers.
Extended Storage
If the transformer is to be stored for an extended period
of time before being placed into service, it should be
placed on a firm level surface.
All space heaters (if supplied) in terminal chambers,
switch cabinets, control cabinets or other enclosures,
must be connected and energized at all times to control
moisture. If it is not practical to energize the control
cabinet space heater, desiccant packets may be used
to control moisture in control cabinets only. Desiccant
packets must be replaced periodically to maintain
effectiveness.
It is recommended that the transformer be inspected
periodically as described below while it is in extended
storage. Results should be recorded and compared
with previous results to ensure that no damage or
change in condition has occurred.
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Small Power Substation Transformers
Document 2.4.54 Revision 0
July 2006
INSTALLATION
Location and Mounting
The transformer should be mounted on a level
concrete foundation of sufficient strength to support
the weight of the completely assembled transformer.
If the transformer is not level, insulating fluid may
not circulate properly through the cooling assembly,
possibly causing overheating and reduced transformer
life. The mounting location should provide for adequate
ventilation and easy access for inspection. The
transformer should be located at least 24 inches from
any obstruction. When installing transformers designed
for indoor operation, adequate air inlets and outlets
must be provided for proper cooling. Avoid locating
transformers in corrosive areas.
Opening Transformer Tank
Transformers are usually shipped sealed and should
not be opened unless necessary.
DANGER: SLOWLY RELEASE INTERNAL
!
TANK ACCESSORIES. FAILURE TO DO SO COULD
RESULT IN SEVERE PERSONAL INJURY, DEATH, OR
PROPERTY DAMAGE.
!
TO ENTER THE TRANSFORMER TANK UNLESS AN
ANALYSIS OF THE AIR IN THE TANK SHOWS AT
LEAST 19.5% OXYGEN. THE GAS SPACE IN AN
OPERATING TRANSFORMER USUALLY CONSISTS
OF NITROGEN GAS. WHENEVER ANYONE IS IN
THE TANK, A PERSON SHOULD BE STATIONED AT
THE HAND HOLE OUTSIDE THE TANK TO ENSURE
SAFETY OF THE PERSON INSIDE.
PRESSURE PRIOR TO REMOVING
DANGER: TO AVOID DEATH FROM
SUFFOCATION NEVER ALLOW ANYONE
If it is necessary to remove some fluid from the tank to
allow for inspection or other work, the transformer must
be refilled with fluid after work is completed.
Personnel should not be permitted on top or inside the
transformer while it is open unless they have emptied
all pockets and checked for loose objects that might fall
into the tank. All tools should be accounted for after
work is completed. It is recommended that any tools
used on top of the transformer or inside the tank be
attached with safety cords to prevent them from being
lost inside the transformer.
Personnel must not stand directly on any electrical
insulation. Clean drop cloths should be used under
working areas in the transformer to prevent objects
from dropping into the core/coil assembly.
The following procedure should be used to remove the
hand hole cover.
1. Thoroughly clean the hand hole cover.
Remove all moisture, dirt, and grease to
avoid contaminating the transformer’s fluid
compartment.
2. Relieve internal tank pressure by manually
operating the pressure relief valve.
3. Remove cover fasteners.
4. Gently pry the cover upward, making sure that
the cover gasket does not fall into the tank.
Lift the cover vertically to prevent damage to
cover, bolts, and gasket.
5. Remove the gasket sections from the
hand hole flange. Record the location and
orientation of each gasket piece so they can be
reinstalled correctly.
Transformer should not remain open for more than
12 hours at a time. If work is interrupted, the tank
should be resealed, evacuated, and filled with dry air or
nitrogen.
To prevent contamination of the transformer tank, do
not open the transformer in an unprotected area during
inclement weather or where the air may contain dirt
or other particles. Either of the above could cause
a transformer failure. The tank opening should be
protected against entry of foreign matter.
The following procedure should be used to reinstall the
hand hole cover.
1. Place gasket sections in their original positions
and orientations.
2. Reinstall hand hole cover. Reinstall fasteners
and torque to 25 ft-lbs. After tightening all
fasteners, re-torque each one to ensure proper
torque.
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Small Power Substation Transformers
3. Pressurize the headspace to 4 PSIG and
check for fluid leaks. This pressure should be
maintained for at least four hours.
When the internal inspection is complete, reseal the
tank and refill with fluid (if any was removed prior to
inspection). The gas space should be filled with dry
air or dry nitrogen to 2 PSIG. Contact the Howard
Substation Transformer Division if any internal damage
is found during the internal inspection.
Installation of Detachable Radiators
When radiators are shipped detached, they should be
installed according to the instructions below.
1. Verify that all valves on the tank are in the
closed position.
2. Remove shipping plates from the valves on the
tank and from the radiator flanges. Take care
not to damage gaskets.
3. Inspect for moisture and contamination
inside the radiator headers. Contact the
Howard Substation Transformer Division if any
contamination is found.
4. Clean all mating surfaces on the tank valves
and radiator flanges and apply a small amount
of petroleum jelly to the gaskets on the tank
valve flanges to hold them in place during
installation of the radiators.
5. Lift the radiators into position using the lifting
eyes on top of the radiators and align holes
in the radiator flanges with holes in the valve
flanges. If fans are provided, attach the
radiators having fans first, then attach the
other radiators.
6. Insert bolts in the top and bottom flanges with
bolt heads adjacent to the transformer tank.
7. Tighten bolts evenly alternating across corners
until metal-to-metal tightness is achieved at all
four corners of each flange
Filling Installed Radiators with Fluid
Follow the steps below to fill installed radiators with
insulating fluid.
DANGER: TRANSFORMER OIL SHOULD
!
FLUID. UNDER SOME CONDITIONS, SEALED
TRANSFORMER TANKS MAY ACCUMULATE
EXPLOSIVE GASES AND THE HANDING OF
TRANSFORMERS MAY GENERATE STATIC
ELECTRICITY. SAFETY PRECAUTIONS BEFORE OILFILLING OR FILTERING SHOULD INCLUDE PURGING
ALL GAS SPACES WITH NITROGEN, GROUNDING
THE TRANSFORMER, ALL BUSHINGS, AND ALL OIL
HANDLING EQUIPMENT. FAILURE TO DO SO COULD
RESULT IN SEVERE PERSONAL INJURY, DEATH, OR
EQUIPMENT DAMAGE.
!
DURING THE VACUUM FILLING OPERATION. THE
TANK SHOULD BE UNDER POSITIVE PRESSURE
DURING PERIODS OF RAIN OR HIGH HUMIDITY
IN ORDER TO PREVENT MOISTURE FROM BEING
DRAWN INTO THE TANK. FAILURE TO FOLLOW
THESE PRECAUTIONS COULD RESULT IN SEVERE
PERSONAL INJURY, DEATH, OR EQUIPMENT
DAMAGE.
During the process do not allow the fluid level to drop
below the top of the core and coil assembly.
fluid level in the transformer becomes too low, stop
the radiator filling procedure and add fluid to the tank
before completing the filling process.
ALWAYS BE HANDLED AS A FLAMMABLE
WARNING: TRANSFORMERS SHOULD
NOT BE LEFT UNDER VACUUM EXCEPT
If the
1. Loosen the top header plugs and slowly open
the bottom radiator valves one at a time to
start the flow of fluid.
2. Add fluid to the tank if necessary during the
process to maintain the proper fluid level in the
tank.
3. After the radiators are filled, open the top
radiator valves.
4. Remove the top header plugs and reinstall
them using Teflon pipe thread tape.
5. Ensure that top and bottom radiator valves on
each radiator are in the full “OPEN” position.
6. Observe the fluid level gauge and ensure that
the fluid level is correct. If the level is low, add
fluid to the tank.
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Small Power Substation Transformers
Document 2.4.54 Revision 0
July 2006
Installation of Surge Arresters
Surge arresters should be installed according to the
following instructions and the outline drawing.
WARNING: FAILURE TO FOLLOW THESE
!
PERSONAL INJURY, DEATH, OR EQUIPMENT
DAMAGE.
INSTRUCTIONS COULD RESULT IN SEVERE
1. Carefully unpack and inspect surge arresters
for damage.
2. When installing arresters, all mounting feet
must be flush with the mounting surface before
tightening bolts. Use shims if necessary.
3. Do not climb or stand on arrester. Do not place
undue mechanical stress on arrester.
4. Use only the lifting devices provided on the
arrester for lifting.
5. Arrester exhaust ports (if supplied) must be
oriented so that exhaust will be directed away
from other arresters and other equipment.
Installation of Air Terminal Chamber and
15 KV and 5 KV Switchgear Adapters
Air terminal chambers are designed to protect
personnel from high voltages and to provide a clean,
dry environment for bushings. Air terminal chambers
must be installed according to instructions on the
drawing. Refer to transformer outline drawing, detail
drawing, and station plan drawing.
WARNING: IMPROPER INSTALLATION OF
!
MAY ALLOW WATER OR OTHER CONTAMINANTS
TO CONTACT LIVE PARTS, POSSIBLY RESULTING IN
SEVERE PERSONAL INJURY, DEATH, OR PROPERTY
DAMAGE.
Securely attach the flexible connectors supplied by
the switchgear manufacturer to the switchgear bus
bars. The number of flexible connectors supplied
is determined by the transformer current and not
by the current rating of the bus bar. Check the
length of flexible connectors and ensure that there
is approximately 0.375 inch (10 mm) of slack. This
will permit some movement of the bus bars to allow
for expansion and contraction and possible settling
of the transformer. Securely attach the ground bus
connection between the transformer and switchgear.
Before reinstalling the adapter housing, check for
CONNECTING CHAMBERS AND ADAPTERS
adequate electrical clearances as indicated on the
outline drawing and check tightness of connections and
supports. Complete the installation by assembling the
housing. Install the adjustable plate and ensure proper
gasket sealing of the switchgear throat.
Pre-energization Tests and Checklist
The following tests and checks should be performed at
a minimum to ensure that the transformer is ready to
be energized. Do not energize the transformer without
performing these tests and checks.
1. Insulating Fluid Test. Draw a fluid sample and
test its dielectric strength. Dielectric strength
of the new fluid should be 26 kV or greater.
2. Pressure Test. Check the transformer tank for
leaks by pressurizing the tank with dry air or
dry nitrogen through the pressure test fitting
to a pressure of 3 to 4 PSIG. Let the tank
stand under pressure for one to two hours,
then examine the tank and fittings for leaks.
Leaks above the fluid level can be detected
by applying soap solution to all welds, joints,
pipe fittings, and cable connections. Upon
completion of this test, reduce the internal
pressure to 1 or 2 PSIG.
3. Insulation Megger Test. Perform a 1000-Volt
Megger test and a power factor test to ensure
that none of the windings are grounded.
4. Ratio Test. Perform a ratio test at each tap
position to ensure that transformer coil ratios
and tap changer connections are correct.
5. Continuity Test and Resistance Test. Perform a
continuity check on each winding.
6. Line Connections. In preparation for making
line connections, check to make sure that
all mating connector surfaces are clean and
smooth. Connections must be tightened
appropriately to prevent overheating and
possible subsequent failure of the connection.
Connections should be made with care to avoid
placing undue stress on the bushings.
7. Tap Changer Setting. Check the tap changer
setting to ensure it is set to the proper position
for the required voltage.
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8. Delta/Wye and Series/Multiple Switch
Settings. Check delta/wye and series/multiple
switch settings to make sure they are set
correctly. If these connections are made using
an internal terminal board, check to ensure
that these connections are made properly
according to the chart on the transformer
nameplate. If the transformer is equipped
with an internal terminal board, refer to page 7
for instructions and warnings prior to opening
tank.
9. Grounding. Check to ensure that the
transformer tank is permanently and effectively
grounded. The transformer tank ground pad is
located near the bottom of the tank.
10. Wiring. Check wiring of control and alarm
circuits (if provided) to make sure there are
no loose connections and no damage to
insulation.
11. Fluid Level. Check to make sure the fluid level
is correct as indicated by the fluid level gauge.
12. Tank Finish. Check all painted surfaces
to make sure that there is no damage or
corrosion.
13. Bolted Connections. Check all bolted
connections for tightness.
14. Tools. Check to make sure that all tools and
equipment are accounted for and have been
removed from the transformer.
15. Fluid Temperature. Read the fluid temperature
gauge and make sure the temperature is no
lower than minus 20°C before the unit is
energized.
Small Power Substation Transformers
10
Small Power Substation Transformers
COMPONENTS AND ACCESSORIES
Document 2.4.54 Revision 0
July 2006
Refer to the outline drawing for a list of accessories
furnished with the transformer.
Transformer Nameplate
A nameplate is supplied on each transformer according
to ANSI standard C57.12.00. The nameplate provides
certain physical and electrical information about the
transformer.
Control Cabinet
Refer to the wiring diagram for a description of electrical
circuits inside the control cabinet. Use caution when
testing alarm switches to prevent damage to the switch.
DANGER: THE CONTROL CABINET
!
ENERIGZE THE CONTROL CABINET VOLTAGE
SUPPLY PRIOR TO PERFORMING WORK INSIDE THE
CONTROL CABINET OR ON EXTERNAL ACCESSORIES
CONNECTED TO EQUIPMENT WITHIN THE CONTROL
CABINET. FAILURE TO DO SO COULD RESULT IN
SEVERE PERSONAL INJURY, DEATH, OR PROPERTY
DAMAGE.
CONTAINS DANGEROUS VOLTAGES. DE-
Pressure/Vacuum Gauge
The pressure/vacuum gauge indicates the pressure in
the tank gas space relative to atmospheric pressure.
The pressure will normally vary as a function of
transformer temperature. If the transformer is lightly
loaded or de-energized during times of low ambient
temperature, the gauge may indicate a negative
pressure.
Pressure/Vacuum gauges can be supplied with an
optional alarm/signal switch. Refer to the schematic
wiring diagram furnished with the transformer.
WARNING: IF THE PRESSURE/VACUUM
!
VARYING LOAD AND AMBIENT CONDITIONS,
THE TRANSFORMER SHOULD BE CHECKED FOR
A POSSIBLE TANK LEAK. A LEAK WILL ALLOW
MOISTURE AND AIR TO ENTER THE TRANSFORMER,
WHICH COULD DEGRADE THE INSULATION AND
FLUID. LEFT UNREPAIRED, LEAKS COULD LIMIT
TRANSFORMER LIFE OR CAUSE A VIOLENT FAILURE
THAT COULD RESULT IN SEVERE PERSONAL INJURY,
DEATH, OR EQUIPMENT DAMAGE.
GAUGE CONSTANTLY READS ZERO UNDER
Alarm Switch Ratings
When control wiring or alarm contacts are provided, refer
to the control wiring diagram, or the outline drawing for
contact type, contact ratings, and terminal locations.
Current Transformers
Current transformers (if provided) are mounted inside
the transformer tank around the transformer line leads.
For cover-mounted bushings, current transformers are
located underneath the transformer cover. For tank-wall
mounted bushings, current transformers are usually
located on top of the core and coil assembly. Current
transformer leads are always terminated inside a
junction box. Refer to the transformer wiring diagram to
identify the wire markings. Current transformer leads
are always shorted and grounded to the tank at the
factory before shipment.
WARNING: CURRENT TRANSFORMER
!
LOAD OR SHORT CIRCUITED TO AVOID DAMAGING
VOLTAGES AT THE TERMINALS. FAILURE TO MAKE
THESE CONNECTIONS COULD RESULT IN SEVERE
PERSONAL INJURY, DEATH, OR PROPERTY DAMAGE.
SECONDARIES MUST BE CONNECTED TO A
Automatic Pressure Relief Device
Small power transformers are sometimes furnished
with a weatherproof, cover-mounted automatic pressure
relief device (PRD) to relieve excessive tank pressures
that might occur during operation of the transformer.
The device consists of a self-resetting, spring-loaded
diaphragm and a visual indicating flag. When gas
pressure in the tank exceeds the PRD’s specified limit,
the gas pressure will open the diaphragm, vent the
excess pressure, and trip the visual indicating flag.
After the internal pressure decreases below the PRD
reseal rating, the valve will automatically close and
reseal the transformer. The visual indicating flag must
be manually reset. The cause of PRD activation should
always be investigated since pressure venting indicates
a potential problem inside the transformer.
WARNING: DO NOT ATTEMPT TO DIS-
!
TO DO SO COULD RESULT IN EQUIPMENT DAMAGE
AND SEVERE PERSONAL INJURY.
ASSEMBLE A PRESSURE RELIEF DEVICE.
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Small Power Substation Transformers
PRDs can be supplied with an optional alarm/signal
switch. Refer to the schematic wiring diagram
furnished with the transformer.
Fluid Level Gauge
The fluid level gauge indicates the fluid level inside the
tank. The transformer tank is filled with fluid at the
factory to the normal level at a reference temperature
of 25°C.
Fluid Temperature Gauge
The fluid temperature gauge indicates the fluid
temperature at the top of the fluid column. The
temperature gauge is mounted in a dry, leak proof
well, permitting removal of the gauge without lowering
the fluid level in the tank. The gauge is furnished with
a resettable drag-hand pointer which indicates the
maximum temperature reached since it was last reset.
The drag-hand can be reset by rotating the magnet at
the center of the dial or, on some models, by pressing a
reset button.
During normal operation the fluid temperature
gauge should read less than the sum of the ambient
temperature and the rated temperature rise. For
example, a 50°C gauge reading at an ambient
temperature of 25°C yields a top oil temperature of
75°C, which is below the transformer’s 85°C rated
temperature rise.
Winding Temperature Gauge
Transformers may be furnished with a gauge that
displays estimated winding hot-spot temperature. The
gauge uses a probe that measures the temperature of
the transformer fluid plus auxiliary heat from a heating
element that is energized by a current transformer
mounted inside the transformer tank.
The gauge’s temperature probe is mounted in a dry
well, permitting removal of the gauge without lowering
the fluid level. The gauge is furnished with a resettable
drag-hand pointer that indicates the maximum
temperature reached since it was last reset. The
drag-hand can be reset by rotating the magnet at the
center of the dial, or on some models, by means of a
pushbutton.
Winding temperature gauges can be supplied with an
alarm/signal switch. Refer to the schematic wiring
diagram furnished with the transformer.
Transformers may be supplied with a thermal overload
relay which is similar in operation to the winding
temperature gauge described above. The relay provides
alarm/signal contacts that close at approximately 100%
and 110% rated load.
Rapid Pressure Rise Relay
The optional rapid pressure rise relay (RPRR) monitors
the rate of pressure rise in the transformer’s gas space
and signals when the rate exceeds a safe threshold.
This signal can trigger circuit breaker operation to
de-energize the transformer and can send an alarm.
The RPRR will not be actuated by normal pressure
variations during operation of the transformer. A
seal-in relay latches the output relay and illuminates
an indicator lamp until the unit is manually reset. The
seal-in relay and associated circuitry is mounted in a
separate control cabinet.
If the RPRR has activated, internal arcing has likely
occurred in the transformer tank, and the cause of such
arcing must be investigated. The following steps are
suggested to determine if there are any damages to the
transformer and if so, to what extent.
1. Using a combustible gas detector, check for
combustible gas products of decomposition
in the gas space. Refer to the operating
instructions that came with the gas detector.
2. Test the RPRR and seal-in relay panel to make
sure they are operating properly. Refer to
instructions furnished with RPRR and seal-in
relay panel.
3. Test for insulation power factor, insulation
resistance tests, and transformer turns ratio.
4. Remove the hand hole cover and inspect the
tank interior for appearance and smell. A
burning odor may be present.
5. Make any other tests which may be appropriate
considering results of the tests listed above.
Transformer Cooling Fans
Optional cooling fans may be provided to increase
the transformer load capability without overheating
the transformer windings. Operation of the fans is
controlled by a contact in the fluid temperature gauge
or winding temperature gauge (when furnished) and
by an “auto/manual” control switch. Controls for the
fans are contained in a control cabinet mounted on the
transformer.
Thermal Overload Relay
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DANGER: ALWAYS DE-ENERGIZE THE FAN
!
MAINTENANCE ON FANS. IN ADDITION, DE-ENERGIZE
THE TRANSFORMER WHEN IT IS POSSIBLE TO COME
CLOSE TO LIVE PARTS. FAILURE TO DO SO COULD
RESULT IN SEVERE PERSONAL INJURY OR DEATH.
FAN GUARDS ARE FURNISHED AND INSTALLED AT
THE FACTORY TO PREVENT ACCIDENTAL CONTACT
WITH ROTATING FAN BLADES. DO NOT REMOVE FAN
GUARDS OR ALLOW PERSONNEL TO REACH INSIDE
A GUARD. DOING SO CAN RESULT IN SERIOUS
PERSONAL INJURY AND EQUIPMENT DAMAGE.
The auto/manual switch determines the mode of
operation for the fan motors. When the switch is in
the “manual” position, fans will operate continuously.
When the switch is in the “auto” position, fans will
be automatically controlled by contacts in the fluid
temperature gauge or winding temperature gauge.
Refer to the schematic wiring diagram provided with the
transformer.
Fan motors are provided with thermal overload
protection. The overload protection is usually contained
within the motor. However, if the motors are located in a
hazardous location, the overload protection device may
be located in the control box. Refer to the wiring diagram
provided with the transformer.
Fan motors have permanently sealed ball bearings
and do not normally require maintenance, except as
explained on page 15.
CIRCUIT WHEN INSTALLING OR PERFORMING
DANGER: DO NOT OPERATE A DE-
!
TRANSFORMER IS TOTALLY DE-ENERGIZED.
FAILURE TO DO SO WILL RESULT IN DAMAGE TO
THE TRANSFORMER AND COULD RESULT IN SEVERE
PERSONAL INJURY OR DEATH. DO NOT RE-ENERGIZE
THE TRANSFORMER UNLESS THE TAP CHANGER IS
FIRMLY LOCKED INTO POSITION.
The tap changer is operated by use of a rotating handle
located on the outside of the transformer tank. Never
operate a de-energized tap changer while the transformer
is energized. Tap changers normally have five or seven
tap positions as indicated on the tap changer dial plate
and the transformer nameplate. A locking mechanism is
provided to lock the tap changer in position and prevent
accidental operation. Do not re-energize the transformer
until the tap changer is firmly locked into a tap position.
The transformer is shipped from the factory with the tap
changer in the rated voltage position, unless otherwise
specified by the customer.
ENERGIZED TAP CHANGER UNLESS THE
Dual-Voltage or Delta/Wye Switch
Transformers designed with dual-voltage windings or
reconnectable delta/wye windings as indicated on the
nameplate are provided with a de-energized two-position
dual-voltage or delta/wye switch. The transformer must
be completely de-energized before operating the switch.
If the transformer is not de-energized before operating
the switch, permanent damage will result.
When fan assemblies are installed by the user, it
is important to permanently remove the drain plug
from the motor housing of each motor. This will allow
condensation to drain from the motor housing.
De-energized Tap Changer
The de-energized tap changer may be used to adjust the
voltage ratio of a transformer while it is de-energized. It
is intended to allow adjustment of the output (secondary)
voltage to the rated value. Do not use the tap changer to
raise or lower the output voltage to any voltage other than
that indicated on the transformer nameplate. If the tap
changer is set to provide an output voltage different from
rated voltage, a high noise level, high core loss, and core
saturation may result.
DANGER: DO NOT OPERATE DUAL-
!
THE TRANSFORMER IS TOTALLY DE-ENERGIZED.
FAILURE TO DO SO WILL RESULT IN DAMAGE TO
THE TRANSFORMER AND COULD RESULT IN SEVERE
PERSONAL INJURY OR DEATH. DO NOT RE-ENERGIZE
THE TRANSFORMER UNLESS THE DUAL-VOLTAGE
OR DELTA/WYE SWITCH IS FIRMLY LOCKED INTO
POSITION AND AT THE PROPER VOLTAGE.
VOLTAGE OR DELTA/WYE SWITCH UNLESS
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Small Power Substation Transformers
High-Voltage Bushings
High-voltage bushings are typically shipped installed in
the unit. If the bushings were removed for shipment,
install the bushings per the manufacturer’s guidelines.
WARNING: DO NOT EXCEED THE
!
BUSHING. GREATER LOADS MAY CAUSE BUSHING
DAMAGE THAT COULD RESULT IN SEVERE
PERSONAL INJURY, DEATH, OR PROPERTY
DAMAGE.
Draw-lead bushings usually require no maintenance
except as described on page 15. Maintenance
instructions for condenser-type bushings are furnished
with the bushings.
CANTILEVER LOAD RATING OF THE
Low-Voltage Bushings
Low-voltage bushings are typically shipped installed in
the unit. If the bushings were removed for shipment,
install the bushings per the manufacturer’s guidelines.
Surge Arresters
Transformers may be furnished with optional
distribution class, intermediate class, or station
class surge arresters. Intermediate and station class
arresters are shipped separately from the transformer
to prevent damage. Upon delivery, unpack the arresters
and carefully inspect them for damage, especially the
porcelain components. Install surge arresters according
to the instructions found on page 9.
Radiators
Transformers are furnished with radiator assemblies
(usually panel type) to dissipate heat from the
transformer. Cooling fans may also be furnished
to provide additional loading capability without
overheating the transformer. Radiator assemblies may
be shipped separately from the transformer to reduce
the shipping size of the transformer and to prevent
damage. When radiators are shipped unattached,
they should be installed in the field according to the
instructions on page 8.
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Small Power Substation Transformers
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MAINTENANCE
DANGER: THE TRANSFORMER MUST BE
!
MAINTENANCE WORK. FAILURE TO DO SO COULD
RESULT IN SEVERE PERSONAL INJURY, DEATH, OR
PROPERTY DAMAGE.
It is the responsibility of the owner to inspect, maintain,
and keep the transformer in proper operating condition.
Report all issues during the warranty period to the
Howard Substation Transformer Division. All warranty
repairs must be made or approved by the Howard
Substation Transformer Division.
!
TO DO SO COULD RESULT IN SEVERE PERSONAL
INJURY, DEATH, OR PROPERTY DAMAGE.
DE-ENERGIZED BEFORE BEGINNING ANY
WARNING: TANK LEAKS MUST BE REPAIRED
IMMEDIATELY UPON DISCOVERY. FAILURE
Periodic Tests and Inspections
The following periodic tests and inspections are
recommended for routine transformer maintenance.
1. Gauge readings (one month after initial
energization and annually thereafter)
readings, ambient temperature, and kVA
load should be measured and recorded. Any
abnormal reading suggests that further
diagnostic testing or inspection should be
done. If pressure/vacuum gauge and/or fluid
level gauge readings suggest a possible tank
leak, perform a pressure test according to
instructions found on page 9 (Pre-energization
Tests and Checklist). Tank leaks must be
repaired immediately to prevent serious
damage to the transformer and danger to life.
2. Cooling fans (annual). Check the cooling fans
(if any) by setting the fan’s “auto/manual”
control switch to the “manual” position.
The fans should rotate at full speed within
approximately five seconds. The fans should
rotate smoothly with minimal vibration.
3. Control wiring (annual). Control wiring should
be checked to insure that wire insulation is
in good condition. The control cabinet and
associated conduit should be inspected to
ensure that weather seals are intact. Control
power supply voltage should be checked and
compared to the voltage stated on the wiring
diagram.
. Gauge
4. Paint finish (annual). Inspect the paint finish
for damage or weathering that exposes the
primer coat or bare metal. Repair any paint
damage that might be found.
5. Fluid dielectric test (annual). Sample the
insulating fluid as described below. The
dielectric strength of the insulating fluid should
measure at least 26 kV.
6. Bushing and surge arrester insulators (annual).
Bushing and surge arrester insulators should
be clean. If the surfaces are excessively dirty,
they should be cleaned while the transformer
is not energized.
7. Bushing terminals (one month after initial
energization and annually thereafter). If the
transformer is energized and under load,
measure bushing terminal temperatures
using an infrared scanner. Excessive bushing
terminal temperature indicates a loose or dirty
connection. If the transformer is not energized,
use a torque measuring device to make sure
terminal connections are tight.
Sampling of Insulating Fluid
Transformers are filled with insulating fluid which
provides electrical insulation within the transformer
tank and transfers heat generated in the coils to the
tank wall and radiators. The fluid is either conventional
transformer oil (mineral oil), Envirotemp® FR3 fluid, or
silicone fluid.
Periodically check the transformer for proper fluid level
by reading the fluid level gauge. Add fluid if necessary.
When adding fluid, add only the same type fluid that is
in the transformer.
It is also recommended that a fluid sample be drawn
annually and tested for dielectric strength. Samples
should be drawn from the bottom of the tank. Use
proper sampling procedures to prevent erroneous test
results. Dielectric strength should measure 26 kV
minimum.
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Gaskets
Visually check all gaskets for cracking or other signs of
deterioration. Replace as necessary. When replacing
a gasket carefully clean mating surfaces to remove
any rust, dirt, transformer fluid, old gasket material, or
other contamination that might prevent a good seal.
Use an appropriate gasket cement when installing new
gaskets. Do not reuse old gaskets. Six months after
replacing a gasket, check and retighten if necessary.
Additional Maintenance Instructions
Contact the Howard Substation Transformer Division for
additional maintenance instructions.
Repair Parts
Repair parts can be ordered from the Howard
Substation Transformer Division. A description of the
part and the transformer serial number will be required
to ensure that the correct part has been ordered.
Warranty Claims
The Howard Substation Transformer Division should
be notified immediately when problems are discovered
during the warranty period. All warranty repairs must
be made or approved by the Howard Substation
Transformer Division.
Small Power Substation Transformers
16
Small Power Substation Transformers
Document 2.4.54 Revision 0
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NOTES
17
Instructions for Installation, Operation, and Maintenance
of Substation Transformers Through 10,000 kVA
Document 2.4.54, Revision 0 (July 2006)
Copyright © 2005, Howard Industries, Inc.
Laurel, Mississippi
Telephone: 601-425-3151
Fax: 601-649-8090
Web: howardtransformers.com
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