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Medium Power Substation Transformers
Document 2.4.06, Reision 2
December 2011
Howard IndustriesSubstation Transformer Diision
InstructionsInstaation, Operation, and Maintenance
of Medium Power Substation Transformers
Document 2.4.06, Reision 2
December 2011
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Document 2.4.06, Reision 2December 2011 Medium Power Substation Transformers
IMPORTANT SAFETY INFORMATION
Read these instructions carefuy before proceeding with instaation, operation, or maintenance of this equipment.
Medium power transformers contain extremey hazardous otages. To preent death, serious persona injury, or property
damage, a information in these instructions shoud be read and obsered. Safe use of this equipment is dependent
on proper instaation, operation, and maintenance procedures.
Certain information in this manua is marked with the words DANGER, WARNING, or CAUTION. DANGER indicates an
imminenty hazardous situation which, if not aoided, wi resut in death, serious persona injury, and property damage.
WARNING indicates a potentiay hazardous situation which, if not aoided, coud resut in death, serious persona
injury, and property damage. CAUTION indicates a potentiay hazardous situation which, if not aoided, may resut in
minor or moderate persona injury, and property damage.
Personne shoud not attempt to serice this equipment unti it has been competey de-energized and a high-otage
and ow-otage bushing terminas hae been propery grounded.
Ony quaied personne shoud insta, maintain, and operate this equipment. Quaied personne are those who are
trained in the instaation, maintenance, and operation of high-otage equipment; trained in the proper use of protectie
equipment (such as rubber goes, safety gasses, protectie cothing, hard hats, etc.); and trained in appropriate rst
aid procedures.
IMPORTANT INFORMATION ABOUT THESE INSTRUCTIONS
The instructions contained herein are intended to be a genera guide for the instaation, operation, and of Howard
Industries medium power transformers, when they are used in typica appications and are operated in norma
enironments. Athough efforts hae been made to ensure accuracy and competeness, these instructions do not
address eery conceiabe appication or circumstance that might be encountered. Features presented herein may
not be present in a transformer designs. Standard and optiona features are subject to change without notice.
Howard Industries makes no representation or warranty with respect to and assumes no responsibiity for the
competeness, accuracy, sufciency, or usefuness of these instructions. Questions regarding instaation, operation,
and maintenance (particuary when encountering unusua or specia circumstances not sufcienty coered by
these instructions) shoud be directed to the Howard Industries Substation Transformer Diision.
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Document 2.4.06, Reision 2December 2011 Medium Power Substation Transformers
RECEIvINg INSPECTION
These instructions appy to medium power transformers
manufactured by Howard Industries. It is important to
read the safety information on Page 2 before attemptingany instaation, operation, or maintenance actiities.
Athough a transformers, components, and accessories
are carefuy inspected and tested prior to shipment,
a thorough receiing inspection shoud be conducted
to detect any damage or oss that might hae occurred
during shipment. The receiing inspection shoud be
done upon receipt and before unoading from the truck
or rai car. Note any damage or discrepancies on the
bi of ading and e a caim with the carrier, and notify
the Howard Substation Transformer Diision prior to
unoading the transformer.
Impact RecorderImpact recorders are proided on a rai shipments
and on some truck shipments. An impact recorder is
a mechanica recording acceerometer that can record
shock and impact from a directions. The impact
recorder records on pressure sensitie chart paper each
impact that has occurred, its magnitude, direction, and
time of occurrence. These impacts are recorded through
three independenty operating styi in each of three
separate axes: ongitudina, atera, and ertica.
The impact recorder shoud be checked for eidenceof possibe damage to the transformer due to impacts
during shipment. This check shoud be performed prior
to unoading the transformer. A representatie of the
shipper shoud be present when the recorder is checked.
Any eidence of damage shoud be noted on the bi of
ading and signed by the shipper’s representatie before
the transformer is accepted. Consut with the Howard
Substation Transformer Diision if shipping damage is
found or suspected.
Refer to the operating manua accompanying the impact
recorder for instructions expaining how to turn off the
recorder and to interpret the chart. If it appears thechart recorder stopped running before arria at the na
destination, the shutdown time shoud be noted and this
fact shoud be brought to the attention of the shipper
representatie and to the Howard Industries Substation
Transformer Diision.
Impacts in any axis of ess than 4 G’s are considered
acceptabe. Impacts in any axis of 4 G’s or greater
indicate rough handing that coud potentiay hae
caused damage to the equipment. If rough handing
is indicated, this fact shoud be noted on the shipping
documents and brought to the attention of the shipperrepresentatie and the Howard Industries Substation
Transformer Diision before proceeding with inspection
of the transformer.
Drawins and Documentslocate a shipping papers, packing ists, outine
drawings, and other pertinent information. Use these
documents and this instruction manua during the
inspection.
The transformer outine drawing indicates the ocations
of namepates and warning abes, and proides physica
dimensions and weights. The namepate proides
eectrica characteristics, winding connections, and
weights. The wiring diagram proides detais of contro,
fan and aarm wiring.
DO NOT REMOvE OR OBSCURE ANY WARNING lABElS
OR NAMEPlATES.
Externa InspectionThe foowing externa inspections shoud be made at a
minimum.
1. Ensure that a equipment, accessories, and
components isted on the bi of ading are
present.
2. Ensure that there are no signs of externa
damage.
3. Ensure that the paint nish has not been
damaged.
4. Ensure that ttings, conduit, wiring, and other
attachments are tight and undamaged.
5. Check for eidence of uid eakage on the tank,
aes, or cooing assembies.
6. Check for damage to bushings.
7. Check for damage to shipping crates, packages,or other materias shipped separatey from the
transformer.
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Medium Power Substation Transformers
Document 2.4.06, Reision 2
December 2011
Tank PressureThe tank acuum/pressure gauge may indicate positie
or negatie when the transformer is receied, depending
on the reatie uid and ambient temperatures. This
indicates that the transformer is seaed effectiey. If the
acuum/pressure gauge reads zero, this may indicate
the possibiity of a tank eak, athough a zero reading can
occur occasionay with changing interna and externa
temperatures. In the case of a zero reading the tank
shoud be pressure tested according to the instructions
on Page 14 (Pre-energization Tests and Checklist).
Report any suspected tank eaks to the Howard
Substation Transformer Diision.
Moisture Test (for units shipped dry)The transformer core and coi assemby was thoroughy
dried before shipping from the factory. Precautionswere taken to ensure that dryness is maintained during
shipment. Since it is possibe that moisture coud
enter the transformer tank due to mishanding or other
causes, perform a dew point test as described beow to
ensure the core and cois are sufcienty dry.
A dew point measurement of the gas inside the
transformer tank can be used to estimate dryness of the
insuation system. Using this technique, it is assumed
that moisture content of the gas is in equiibrium with
the moisture content at the surface of the insuation
materia.
The dew point test shoud be performed as described
beow. The easiest way to ensure reasonabe accuracy
is to take the dew point and temperature measurements
during the eary morning hours, when the ambient
temperature and the insuation temperature are in
equiibrium. The gas in the transformer tank shoud be
at a sight positie pressure (5 PSI max.) when the dew
point measurement is made.
1. Use a dew point tester to measure the dew point
of the gas inside the transformer tank.
2. Using Chart A (Page 6), conert the dew point
measurement to apor pressure.
3. Measure the temperature of the insuating
materia.
4. Using Chart B (Page 6), estimate the moisture
content of the insuating materia.
5. Moisture content aboe the cure is in the
acceptabe range. Moisture content beow the
cure is excessie and shoud be brought to the
attention of the Howard Industries Substation
Transformer Diision before proceeding.
Interna InspectionAn interna inspection of the transformer tank is
rarey necessary and is required ony when there are
indications that the transformer has receied seere
impact damage during transit. If an interna inspection
is necessary, foow the instructions on Page 10 for
opening the transformer tank. Contact the Howard
Substation Transformer Diision before proceeding with
any interna inspection.
It is important to foow a carefu receiing inspection
program to record the condition of the transformer when
receied and to identify the source of any damage that
may hae occurred during shipping and handing. A
compete inspection of the transformer and detached
parts shoud be made as soon as possibe to identify any
such damage.
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Document 2.4.06, Reision 2December 2011 Medium Power Substation Transformers
vapor Pressure (Micrometers of Mercury)
D e w P o i n t T e m p e r a t u r e ( ° C )
+20
+10
0
-10
-20
-30
-40
-50
-70
-60
10 100 1,000 10,000
6
TABlE A: Conersion of dew point in degrees centigrade to apor pressure in micrometers of mercury
I n s u l a t i o n T e m p e r a t u r e ( ° C )
vapor Pressure (Micrometers of Mercury)
10 100 1,000 10,000
TABlE B: Moisture equiibrium chart showing acceptabe and unacceptabe moisture imits.
+80
+70
+60
+50
+30
+20
+10
0
+40
Acceptabe rane is aboe the cure
Unacceptabe rane is beow the cure `
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Document 2.4.06, Reision 2December 2011 Medium Power Substation Transformers
STORAgE
Transformer StoraeTransformers can be stored if propery prepared. It is
recommended that stored transformers be competeyassembed. Prior to storage, transformers shoud be
pressure tested according to the instructions on Page
14 (Pre-energization Tests and Checklist). The gas
space aboe insuating uid shoud be pressurized with
dry nitrogen to a pressure of between two to three PSIG.
This wi preent a negatie interna pressure which
might draw moisture into the tank. Transformers not
designed for outdoor use must be stored indoors. If
the transformer is not competey assembed, separate
components and accessories shoud be stored in a
cean dry area in their origina shipping containers.
Transformer uid containers or totes shoud be coered
or stored in a protected area to preent exposure to
rain water or other contaminants. Condenser bushings
shoud be stored in an upright position.
Extended StoraeIf the transformer is to be stored for an extended period
of time before being paced into serice, it shoud
be paced on a rm ee surface. The foowing test
procedure shoud be used prior to storage (in addition
to foowing the Receiving Inspection instructions
on Pages 4 and 5 and Transformer Storage
recommendations on this page).
1. Measure and record ambient temperature andbarometric pressure (for correction of test data).
2. Pressure test the tank using the procedure on
Page 14 (Pre-energization Tests and Checklist)
and check for uid eaks. Foowing pressure
test, reduce tank pressure to two (2) PSIG.
3. Test insuating uid for dieectric strength and
moisture content.
4. Test insuation with a 1000-vot or 2500-vot
Megger test set. (Omit if bushings hae not been
instaed.)
5. Measure insuation power factor using Dobe or
simiar test set. (Omit if bushings hae not beeninstaed.)
6. Measure coi ratios in each tap position to
ensure proper operation of the de-energized
tap changer. (Omit if bushings hae not been
instaed.)
7. Obsere uid ee gauge to erify proper uid
ee.
Sidewa-mounted bushings, if exposed and not
contained in a termina chamber or switch encosure,
shoud be protected from moisture and utraioet
damage with an appropriate coering. This coering
shoud be checked periodicay to ensure it is intact.
Coer-mounted bushings which are shipped separatey
from the transformer shoud be stored in a cean,
dry ocation in their origina shipping cartons. These
bushings shoud be carefuy inspected for damage prior
to instaation on the transformer.
A space heaters (if suppied) in termina chambers,
switch cabinets, contro cabinets or other encosures,
must be connected and energized at a times to contro
moisture. Desiccant packets may be used to contro
moisture in contro cabinets ony, if it is not practica to
energize the contro cabinet space heater. Desiccant
packets must be repaced periodicay to maintain
effectieness.
It is recommended that the transformer be inspected
periodicay as described beow whie it is in extended
storage. Resuts shoud be recorded and compared with
preious resuts to ensure that no damage or change in
condition has occurred.
Quartery InspectionThe quartery inspection described beow shoud be
performed after the rst month of storage and then
quartery thereafter.
1. Inspect protectie coering on sidewa-mounted
bushings. Repace coering if damaged.
2. Inspect space heaters to ensure they are
working propery. Inspect desiccant packets (if
any) in contro cabinets; repace if necessary.
3. Record uid-ee and pressure/acuum
gauge readings. Ensure that tank pressure ismaintained at approximatey 2 PSIG.
4. Measure and record ambient temperature and
barometric pressure.
5. If acuum/pressure gauge or uid ee gauge
readings indicate a possibe tank eak, perform
a tank pressure test according to instructions
found on Page 14 (Pre-energization Tests and
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Document 2.4.06, Reision 2
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Checklist). Any eaks found shoud be repaired
immediatey and then rechecked during
subsequent inspections.
6. Transformer uid containers or totes shoud be
isuay inspected for damage and any indication
of water intrusion or other contamination.
Annua InspectionThe annua inspection shoud incude the foowing
checks in addition to the quartery inspection checks
isted aboe.
1. Check paint nish and repair any damage.
2. Test insuating uid for dieectric strength and
moisture content.
3. Test insuation with a Megger test set. (Omit if
bushings hae not been instaed.)
4. Check insuation power factor with a Dobe or
simiar test set. (Omit if bushings hae not beeninstaed.)
5. Transformer uid containers or totes shoud be
isuay inspected for damage and any indication
of water intrusion or other contamination.
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Document 2.4.06, Reision 2December 2011 Medium Power Substation Transformers
location and MountinThe transformer shoud be mounted on a ee concrete
foundation of sufcient strength to support the weightof the competey assembed transformer. If the
transformer is not ee, insuating uid may not circuate
propery through the cooing assemby, possiby causing
oerheating and reduced transformer ife. The mounting
ocation shoud proide for adequate entiation and
easy access for inspection. The transformer shoud be
ocated at east 24 inches from any obstruction. When
instaing transformers designed for indoor operation,
adequate air inets and outets must be proided for
proper cooing. Aoid ocating transformers in corrosie
areas.
Openin Transformer TankTransformers are usuay shipped seaed and shoud not
be opened uness necessary. Opening the transformer
wi be necessary when transformers are shipped without
bushings, when interna ed connections are required,
or when core ground tests are required.
DANgER: SlOWlY RElEASE INTERNAl
PRESSURE PRIOR TO REMOvING TANK
ACCESSORIES. FAIlURE TO DO SO COUlD RESUlT
IN SEvERE PERSONAl INJURY, DEATH, OR PROPERTY
DAMAGE.
DANgER: TO AvOID DEATH FROM
SUFFOCATION NEvER AllOW ANYONE 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 MANHOlE
OUTSIDE THE TANK TO ENSURE SAFETY OF THE
PERSON INSIDE.
Transformer shoud not remain open for more than24 hours at a time. If work is interrupted, the tank
shoud be reseaed, eacuated, and ed with dry air or
nitrogen.
To preent contamination of the transformer tank, do
not open the transformer in an unprotected area during
incement weather or where the air may contain dirt
or other partices. Either of the aboe coud cause
a transformer faiure. The tank opening shoud be
protected against entry of foreign matter.
If it is necessary to remoe some uid from the tank to
aow for inspection or other work, the transformer mustbe reed with uid after work is competed.
Personne shoud not be permitted on top or inside the
transformer whie it is open uness they hae emptied
a pockets and checked for oose objects that might fa
into the tank. A toos shoud be accounted for after
work is competed. It is recommended that any toos
used on top of the transformer or inside the tank be
attached with safety cords to preent them from being
ost inside the transformer.
Personne must not stand directy on any eectrica
insuation. Cean drop coths shoud be used under
working areas in the transformer to preent objects from
dropping into the core/coi assemby.
The foowing procedure shoud be used to remoe the
manhoe coer.
1. Thoroughy cean the manhoe coer.
Remoe a moisture, dirt, and grease to
aoid contaminating the transformer’s uid
compartment.
2. Reiee interna tank pressure by manuay
operating the pressure reief ae.
3. Remoe coer fasteners.
4. Genty pry the coer upward, making sure that
the coer gasket does not fa into the tank. lift
the coer erticay to preent damage to coer,
bots, and gasket.
5. Remoe the gasket sections from the manhoe
ange. Record the ocation and orientation of
each gasket piece, so they can be reinstaed
correcty.
The foowing procedure shoud be used to reinsta the
manhoe coer.
1. Pace gasket sections in their origina positionsand orientations.
2. Reinsta manhoe coer. Reinsta fasteners
and torque to 25 ft-bs. After tightening a
fasteners, re-torque each one to ensure proper
torque.
3. Remoe the pressure reief ae and pressurize
the headspace and check for uid eaks. Do not
exceed 7 PSIG during this test. This pressure
shoud be maintained for at east four hours.
INSTAllATION
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When interna work is being done on the transformer,
dry air shoud be used to entiate the inside of the tank.
Dry air can be obtained in high-pressure cyinders or
from desiccant-type air-drying equipment. When using
dry air, the foowing precautions shoud be obsered.
1. The temperature of dry air entering thetransformer shoud equa to or greater than the
temperature of the transformer uid and at east
10°F higher than the dew point of the ambient
air.
2. The dry air ow shoud be directed so as to
continuousy purge the transformer gas space.
3. The dew point in the tank gas space shoud
neer exceed 20°F.
Whie the tank is open, the foowing tests shoud be
conducted.
1. A ratio test shoud be made on a windingsand on each tap position. Contact the Howard
Industries Substation Transformer Diision if any
measurement is off-ratio by more than 0.5%.
2. Insuation resistance of each winding to a
other windings and from each winding to ground
shoud be measured. (Coi windings must be
competey coered with uid.) Record the
temperature of the uid. These readings shoud
be comparabe with factory measurements.
3. Disconnect the core ground connection, when
accessibe, on core-form transformers and
measure the resistance from the core to thetank or end frames, using a 1000-vot Megger
test set. The resistance shoud exceed 100
megohms if the core is not coered with uid or
200 megohms if the core is coered with uid.
When the interna inspection is compete, resea the
tank and re with uid (if any was remoed prior to
inspection). The gas space shoud be ed with dry
air or dry nitrogen. Contact the Howard Substation
Transformer Diision if any interna damage is found
during the interna inspection.
Instaation of Detachabe RadiatorsWhen radiators are shipped detached, they shoud be
instaed according to the instructions beow.
1. verify that a aes on the tank are in the
cosed position.
2. Remoe shipping pates from the aes on the
tank and from the radiator anges. Take care
not to damage gaskets.
3. Inspect for moisture and contamination
inside the radiator headers. Contact the
Howard Substation Transformer Diision if any
contamination is found.
4. Cean a mating surfaces on the tank aes
and radiator anges and appy a sma amount
of petroeum jey to the gaskets on the tank
ae anges to hod them in pace during
instaation of the radiators.
5. lift the radiators into position using the ifting
eyes on top of the radiators and aign hoes
in the radiator anges with hoes in the ae
anges. If fans are proided, attach the
radiators haing fans rst, then attach the other
radiators.
6. Insert bots in the top and bottom anges, with
bot heads adjacent to the transformer tank.
7. Tighten bots eeny, aternating across corners,
unti meta-to-meta tightness is achieed at a
four corners of each ange.
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Document 2.4.06, Reision 2December 2011 Medium Power Substation Transformers
Fiin Instaed Radiators with FuidFoow the steps beow to instaed radiators with
insuating uid.
DANgER: TRANSFORMER OIl SHOUlD
AlWAYS BE HANDlED AS A FlAMMABlE FlUID.
SEAlED TRANSFORMER TANKS MAY UNDER SOME
CONDITIONS ACCUMUlATE EXPlOSIvE GASES, AND
HANDING OF TRANSFORMERS MAY GENERATE
STATIC ElECTRICITY. SAFETY PRECAUTIONS BEFORE
OIl-FIllING OR FIlTERING SHOUlD INClUDE
PURGING All GAS SPACES WITH NITROGEN AND
GROUNDING THE TRANSFORMER, All BUSHINGS,
AND All OIl HANDlING EQUIPMENT. FAIlURE TO DO
SO COUlD RESUlT IN SEvERE PERSONAl INJURY,
DEATH, OR EQUIPMENT DAMAGE.
WARNINg: TRANSFORMERS SHOUlD NOT BE
lEFT UNDER vACUUM EXCEPT 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.
Eery container or tote of transformer uid used in the
ing process shoud be isuay inspected and tested
for water and other possibe contaminants beforeproceeding with the ing process.
During the process do not aow the uid ee to drop
beow the top of the core and coi assemby. If the
uid ee in the transformer becomes too ow, stop the
radiator ing procedure and add uid to the tank before
competing the ing process.
1. loosen the top header pugs and sowy open
the bottom radiator aes one at a time to start
the ow of uid.
2. Add uid to the tank if necessary during the
process to maintain uid ee in the tank at its
proper ee.
3. After the radiators are ed, open the top
radiator aes.
4. Remoe the top header pugs and reinsta them
using Teon pipe thread tape.
5. Ensure that top and bottom radiator aes on
each radiator are in the fu “OPEN” position.
6. Obsere the uid ee gauge and ensure that
the uid ee is correct. If the ee is ow, add
uid to the tank.
Instaation of Hih-votae BushinsTransformers are usuay furnished with draw-ead or
condenser type high-otage bushings. If bushings
were remoed prior to shipment and shipped separatey
from the transformer, insta them according to the
instructions beow.
WARNINg: DO NOT OvERSTRESS BUSHINGS
WHEN MAKING CONNECTIONS TO AvOID
DAMAGE. DAMAGED BUSHINGS COUlD CAUSE
SEvERE PERSONAl INJURY, DEATH, OR PROPERTY
DAMAGE.
Instaation of Draw-lead BushinsIf draw-ead type bushings are furnished, insta each
bushing as foows.
1. Remoe the bind ange coering the bottom
end of the bushing.
2. locate and uncoi the draw ead.
3. Insta the gasket suppied with the bushing to
the bushing boss. For cork-neoprene gaskets,
appy a uniform coating of gasket cement to
the gasket area of the bushing boss and to the
bottom of the gasket. Aow cement to become
tacky and then position gasket on the bushing
boss. Then appy a thin coating of petroatumto the top surface of the cork-neoprene gasket.
For nitrie or iton gaskets, appy a thin coating
of petroeum jey to the bottom surface of the
gasket and pace the gasket in the center of the
gasket area on the bushing boss.
WARNINg: WHEN APPlYING GASKET
CEMENT, KEEP All SPARKS AND FlAMES
AWAY FROM WORK AREA. AvOID BREATHING lARGE
QUANTITIES OF vAPOR AND AvOID CONTINUOUS OR
EXCESSIvE CONTACT WITH SKIN. FAIlURE TO DO SO
COUlD RESUlT IN SEvERE PERSONAl INJURY OR
DEATH.
4. Insert a sh wire through the bushing porceain
and attach the bottom end of it to the top of the
termina on the end of the draw ead.
5. Straighten the draw ead, so that it is free of
twists and kinks.
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6. Using the sh wire, carefuy pu the draw-ead
through the bushing, taking care not to damage
the insuation on the ead.
7. Insta the bushing mounting hardware and
fuy tighten by aternatey tightening opposite
corners. For bushings with porceain ange and
camping ange, torque hardware to 8 ft-bs.
For bushings with meta ange, tighten unti the
bushing ange has contacted the bushing boss
and ock washers are attened.
8. Rotate the termina unti the stee pin pressed
in the draw ead seats in the sot inside the
porceain top end. With the pin seated in the
grooe, approximatey 1/2 inch of thread shoud
protrude aboe the porceain top. If the ead
appears to be too short, a probem may exist
that shoud be corrected before proceeding.
9. Appy a thin coating of petroeum jey to the topsurface of the termina cap seaing gasket and
press the coated surface into the gasket recess
in the termina cap.
10. Remoe the sh wire taking care to preent
the draw ead from sipping back inside the
porceain bushing.
11. Insta the termina cap on the draw ead
termina and hand tighten, being carefu to
keep the stee pin seated in the sot inside the
porceain top.
12. verify that the gasket is propery seated and the
termina cap is centered on the porceain.
13. Torque the termina cap to 35 ft-bs.
14. Test for gasket eaks by pressurizing the
transformer with dry air or nitrogen to a
pressure of approximatey 2-3 PSIG and
appying a soap bubbe soution.
Instaation of Condenser BushinsIf condenser type bushings are furnished, insta them
according to the instruction iterature shipped with the
bushings. These instructions wi coer instaation
maintenance, and use of the power factor test termina.
vacuum Oi Fi ProcessThis procedure is for the acuum oi ing of a
transformer. This procedure appies for transformers
which hae been shipped dry air ed. It aso appies
if the oi ee in the transformer has been owered to
a ee that exposes part or a of the cois to air at anytime during the instaation of the transformer.
1. Check a radiators to be sure the radiator aes
are in the open positions and to erify that a
the radiator anges are tightened.
2. Check a high otage bushing bot anges and
a ow otage bushing bot anges and be sure
a are propery tightened.
3. If the manhoe access coer has been remoed
for any reason erify that the bots securing the
manhoe coer(s) are propery tightened.
4. Connect the acuum pump suction ine to the
tank coer tting. If the transformer has an OlTC
then acuum must be appied to the OlTC tank
at the same time as the main tank is acuumed.
Connect acuum ines and pu a acuum on the
OlTC tank.
5. Connect the oi ine to the tank at the bottom
drain ae connection.
6. Start the acuum pump.
7. When the acuum ee inside the tank reaches
500 microns (500 miiTorr) start timing and
when this acuum ee has been maintained for
24 hours the oiing may be started. Oiing
rate to be 30 – 40 gpm.
8. Continue to unti the oi gauge registers
sighty aboe the 25 C oi ee.
9. After the oi ing has been competed continue
to hod the acuum ee for 1 additiona hour.
10. The acuum pump may now be stopped. Use
dry nitrogen to ent the transformer tank.
11. After the transformer has been ed with oi
it shoud be aowed to sit for 24 hours before
energizing in order to aow bubbes of gas
(which hae been pued out of soution by the
acuum ing process) to be reabsorbed by the
oi.
12. At any time during the instaation of the
transformer if the oi ee in the transformer
has been owered to a ee that exposes part or
a of the cois to air, the oi must be competey
remoed and the aboe procedure foowed.
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14
Instaation of Sure ArrestersSurge arresters shoud be instaed according to the
foowing instructions and the outine drawing.
WARNINg: FAIlURE TO FOllOW THESE
INSTRUCTIONS COUlD RESUlT IN SEvEREPERSONAl INJURY, DEATH, OR EQUIPMENT DAMAGE.
1. Carefuy unpack and inspect surge arresters for
damage.
2. When instaing arresters, a mounting feet
must be ush with the mounting surface before
tightening bots. Use shims if necessary.
3. Do not cimb or stand on arrester. Do not pace
undue mechanica stress on arrester.
4. Use ony the ifting deices proided on the
arrester for ifting.
5. Arrester exhaust ports (if suppied) must be
oriented so that exhaust wi be directed away
from other arresters and other equipment.
Instaation of Air Termina Chamber and
15 Kv and 5 Kv Switchear AdaptersAir termina chambers are designed to protect
personne from high otages and to proide a cean, dry
enironment for bushings. Air termina chambers must
be instaed according to instructions on the drawing.
Refer to transformer outine drawing, detai drawing, and
station pan drawing.
WARNINg: IMPROPER INSTAllATION OF
CONNECTING CHAMBERS AND ADAPTERS
MAY AllOW WATER OR OTHER CONTAMINANTS
TO CONTACT lIvE PARTS, POSSIBlY RESUlTING IN
SEvERE PERSONAl INJURY, DEATH, OR PROPERTY
DAMAGE.
Securey attach the exibe connectors to the switchgear
bus bars (The number of exibe connectors suppied
is determined by the transformer current and not
by the current rating of the bus bar.). Check theength of exibe connectors and ensure that there is
approximatey 0.375 inch (10 mm) of sack. This wi
permit some moement of the bus bars to aow for
expansion and contraction and possibe setting of the
transformer. Securey attach the ground bus connection
between the transformer and switchgear. Before
reinstaing the adapter housing, check for adequate
eectrica cearances as indicated on the outine drawing
and check tightness of connections and supports.
Compete the instaation by assembing the housing.
Insta the adjustabe pate and ensure proper gasket
seaing of the switchgear throat.
Pre-enerization Tests and CheckistThe foowing tests and checks shoud 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. Insuating Fuid Test. Draw a uid sampe and
test its dieectric strength. Dieectric strength of
new uid shoud be 26 kv or greater.
2. Pressure Test. Check the transformer tank for
eaks by pressurizing the tank with dry air or
dry nitrogen through the pressure test tting toa pressure of 3 to 4 PSIG. let the tank stand
under pressure for one to two hours, then
examine the tank and ttings for eaks. leaks
aboe the uid ee can be detected by appying
soap soution to a weds, joints, pipe ttings,
and cabe connections. Upon competion of this
test, reduce the interna pressure to 1 or 2 PSIG.
3. Insuation Megger Test. Perform a 1000-vot
Megger test and a power factor test to ensure
that none of the windings is grounded.
4. Ratio Test. Perform a ratio test at each tap
position to ensure that transformer coi ratios
and tap changer connections are correct.
5. Continuity Test and Resistance Test. Perform
a continuity check on each winding. Measure
the winding resistance of each winding and
compare resuts to factory test aues. An
increase of more than 10% coud indicate a
oose interna connection.
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15
6. line Connections. In preparation for making
ine connections, check to make sure that
a mating connector surfaces are cean and
smooth. Connections must be tightened
appropriatey to preent oerheating and
possibe subsequent faiure of the connection.Connections to shoud be made with care to
aoid pacing undue stress on the bushings.
Refer to bushing connection information on
Pages 12 and 13.
7. Tap Changer Setting. Check the tap changer
setting to ensure it is set to the proper position
for the required otage.
8. Deta/Wye and Series/Mutipe Switch Settings.
Check deta/wye and series/mutipe switch
settings to make sure they are set correcty. If
these connections are made using an interna
termina board, check to ensure that theseconnections are made propery according to
the chart on the transformer namepate. If
the transformer is equipped with an interna
termina board, refer to Page 10 for instructions
and warnings prior to opening tank.
9. Grounding. Check to ensure that the
transformer tank is permanenty and effectiey
grounded. The transformer tank ground pad is
ocated near the bottom of the tank.
10. Wiring. Check wiring of contro and aarm
circuits (if proided) to make sure there are no
oose connections and no damage to insuation.11. Fuid lee. Check to make sure the uid
ee as indicated by the uid ee gauge is as
indicated on Page 17.
12. Tank Finish. Check a painted surfaces to
make sure that there is no damage or corrosion.
13. Boted Connections. Check a boted
connections for tightness.
14. Toos. Check to make sure that a toos and
equipment are accounted for and hae been
remoed from the transformer.
15. Fuid Temperature. Read the uid temperature
gauge and make sure the temperature is noower than minus 20°C before the unit is
energized.
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Refer to the outine drawing for a ist of accessories
furnished with the transformer.
Transformer NamepateA namepate is suppied on each transformer according
to ANSI standard C57.12.00. The namepate proides
certain physica and eectrica information about the
transformer.
Contro CabinetRefer to the wiring diagram for a description of eectrica
circuits inside the contro cabinet. Use caution when
testing aarm switches to preent damage to the switch.
DANgER: THE CONTROl CABINET
CONTAINS DANGEROUS vOlTAGES. DE-
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.
Aarm Switch Ratins
When contro wiring or aarm contacts are proided, referto the contro wiring diagram, or the outine drawing for
contact type, contact ratings, and termina ocations.
Current TransformersCurrent transformers (if proided) are mounted inside
the transformer tank around the transformer ine eads.
For coer-mounted bushings, current transformers are
ocated underneath the transformer coer. For tank-wa
mounted bushings, current transformers are usuay
ocated on top of the core and coi assemby. Current
transformer eads are aways terminated inside a
junction box. Refer to the transformer wiring diagram toidentify the wire markings. Current transformer eads
are aways shorted and grounded to the tank at the
factory before shipment.
WARNINg: CURRENT TRANSFORMER
SECONDARIES MUST BE CONNECTED TO A
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.
Pressure/vacuum gaueThe pressure/acuum gauge indicates the pressure in
the tank gas space reatie to atmospheric pressure.
The pressure wi normay ary as a function of
transformer temperature. If the transformer is ighty
oaded or de-energized during times of ow ambient
temperature, the gauge may indicate a negatie
pressure.
Pressure/vacuum gauges can be suppied with an
optiona aarm/signa switch. Refer to the schematic
wiring diagram furnished with the transformer.
WARNINg: IF THE PRESSURE/vACUUM
GAUGE CONSTANTlY READS ZERO UNDERvARYING 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.
Automatic Pressure Reief DeiceMedium power transformers are usuay furnished with
a weatherproof, coer-mounted automatic pressure
reief deice (PRD) to reiee excessie tank pressures
that might occur during operation of the transformer.
The deice consists of a sef-resetting, spring-oaded
diaphragm and a isua indicating ag. When gas
pressure in the tank exceeds the PRD’s specied imit,
the gas pressure wi open the diaphragm, ent the
excess pressure, and trip the isua indicating ag.
After the interna pressure decreases beow the PRD
resea rating, the ae wi automaticay cose and
resea the transformer. The isua indicating ag mustbe manuay reset. The cause of PRD actiation shoud
aways be inestigated, since pressure enting indicates
a potentia probem inside the transformer.
COMPONENTS AND ACCESSORIES
16
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17
Winding temperature gauges can be suppied with an
aarm/signa switch. Refer to the schematic wiring
diagram furnished with the transformer.
Therma Oeroad ReayTransformers may be suppied with a therma oeroad
reay, which is simiar in operation to the winding
temperature gauge described aboe. The reay proides
aarm/signa contacts that cose at approximatey 100%
and 110% rated oad.
Rapid Pressure Rise ReayThe optiona Rapid Pressure Rise Reay (RPRR) monitors
the rate of pressure rise in the transformer’s gas space
and signas when the rate exceeds a safe threshod.
This signa can trigger circuit breaker operation to de-
energize the transformer and can send an aarm. The
RPRR wi not be actuated by norma pressure ariationsduring operation of the transformer. A sea-in reay
atches the output reay and iuminates an indicator
amp unti the unit is manuay reset. The sea-in reay
and associated circuitry is mounted in a separate contro
cabinet.
If the RPRR has actiated, interna arcing has ikey
occurred in the transformer tank, and the cause of such
arcing must be inestigated. The foowing steps are
suggested to determine the extent of damage to the
transformer, in any.
1. Using a combustibe gas detector, check for
combustibe gas products of decompositionin the gas space. Refer to the operating
instructions that came with the gas detector.
2. Test the RPRR and sea-in reay pane to make
sure they are operating propery. Refer to
instructions furnished with RPRR and sea-in
reay pane.
3. Test for insuation power factor, insuation
resistance tests, and transformer turns ratio.
4. Remoe the manhoe coer and inspect the tank
interior for appearance and sme. (A burning
odor may be present.)
5. Make any other tests which may be appropriate
considering resuts of the tests isted aboe.
WARNINg: DO NOT ATTEMPT TO
DISASSEMBlE A PRESSURE RElIEF DEvICE.
TO DO SO COUlD RESUlT IN EQUIPMENT DAMAGE
AND SEvERE PERSONAl INJURY.
PRD’s can be suppied with an optiona aarm/signaswitch. Refer to the schematic wiring diagram furnished
with the transformer.
Fuid lee gaueThe uid ee gauge indicates the uid ee inside the
tank. The transformer tank is ed with uid at the
factory to the norma ee at a reference temperature of
25°C.
Fuid Temperature gaueThe uid temperature gauge indicates the uid
temperature at the top of the uid coumn. Thetemperature gauge is mounted in a dry, eak proof
we, permitting remoa of the gauge without owering
the uid ee in the tank. The gauge is furnished with
a resettabe drag-hand pointer which indicates the
maximum temperature reached since it was ast reset.
The drag-hand can be reset by rotating the magnet at
the center of the dia or, on some modes, by pressing a
reset button.
During norma operation the uid temperature
gauge shoud read ess than the sum of the ambient
temperature and the rated temperature rise. For
exampe, a 50°C gauge reading at an ambient
temperature of 25°C yieds a top oi temperature of
75°C, which is beow the transformer’s 85°C rated
temperature rise.
Windin Temperature gaueTransformers may be furnished with a gauge that
dispays estimated winding hot-spot temperature. The
gauge uses a probe that measures the temperature of
the transformer uid pus auxiiary heat from a heating
eement that is energized by a current transformer
mounted inside the transformer tank.
The gauge’s temperature probe is mounted in a dry we,
permitting remoa of the gauge without owering the
uid ee. The gauge is furnished with a resettabe drag-
hand pointer that indicates the maximum temperature
reached since it was ast reset. The drag-hand can be
reset by rotating the magnet at the center of the dia, or
on some modes, by means of a pushbutton.
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18
Transformer Cooin FansOptiona cooing fans may be proided to increase
the transformer oad capabiity without oerheating
the transformer windings. Operation of the fans is
controed by a contact in the uid temperature gauge
or winding temperature gauge (when furnished) andby an “auto/manua” contro switch. Contros for the
fans are contained in a contro cabinet mounted on the
transformer.
DANgER: AlWAYS DE-ENERGIZE THE FAN
CIRCUIT WHEN INSTAllING OR PERFORMING
MAINTENANCE ON FANS. IN ADDITION, DE-ENERGIZE
THE TRANSFORMER WHEN IT IS POSSIBlE TO COME
ClOSE TO ElECTRICAllY CHARGED/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/manua switch determines the mode of
operation for the fan motors. When the switch is in
the “manua” position, fans wi operate continuousy.
When the switch is in the “auto” position, fans wi
be automaticay controed by contacts in the uid
temperature gauge or winding temperature gauge.Refer to the schematic wiring diagram proided with the
transformer.
Fan motors are proided with therma oeroad
protection. The oeroad protection is usuay contained
within the motor. Howeer, if the motors are ocated in a
hazardous ocation, the oeroad protection deice may
be ocated in the contro box. Refer to the wiring diagram
proided with the transformer.
Fan motors hae permanenty seaed ba bearings
and do not normay require maintenance, except as
expained on Page 20.
When fan assembies are instaed by the user, it
is important to permanenty remoe the drain pug
from the motor housing of each motor. This wi aow
condensation to drain from the motor housing.
De-Enerized Tap ChanerThe de-energized tap changer may be used to adjust the
otage ratio of a transformer whie it is de-energized.
It is intended to aow adjustment of the output
(secondary) otage to the rated aue. Do not use the
tap changer to raise or ower the output otage to anyotage other than that indicated on the transformer
namepate. If the tap changer is set to proide an output
otage different from rated otage, a high noise ee,
high core oss, and core saturation may resut.
DANgER: DO NOT OPERATE A DE-ENERGIZED
TAP CHANGER UNlESS 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 TAP CHANGER IS FIRMlY lOCKED INTO
POSITION.
The tap changer is operated by use of a rotating
hande ocated on the outside of the transformer tank.
Neer operate a de-energized tap changer whie the
transformer is energized. Tap changers normay hae
e or seen tap positions as indicated on the tap
changer dia pate and the transformer namepate. A
ocking mechanism is proided to ock the tap changer
in position and preent accidenta operation. Do not
re-energize the transformer unti the tap changer is rmy
ocked into a tap position.
The transformer is shipped from the factory with the tap
changer in the rated otage position, uness otherwise
specied by the customer.
Dua-votae or Deta/Wye SwitchTransformers designed with dua-otage windings or
reconnectabe deta/wye windings as indicated on the
namepate are proided with a de-energized two-position
dua-otage or deta/wye switch. The transformer must
be competey de-energized before operating the switch.
If the transformer is not de-energized before operating
the switch, permanent damage wi resut.
WARNINg: DO NOT OPERATE DUAl-vOlTAGE OR
DElTA/WYE SWITCH UNlESS 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.
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On-load Tap ChanerSome transformers are proided with an on-oad tap
changer that can change taps whie under oad, thereby
reguating the output otage. A user-programmabe
contro unit automaticay operates the on-oad tap
changer to maintain the seected output otage. Referto the manua proided with the on-oad tap changer for
warnings and for operating and maintenance
instructions.
Hih-votae BushinsTransformers are normay suppied with draw-ead
or condenser type high-otage bushings. If bushings
were remoed for shipment, insta draw-ead bushings
according to instructions found on Pages 12 and 13,
and insta condenser-type bushings according to
instructions furnished with the transformer.
WARNINg: DO NOT EXCEED THE CANTIlEvER
lOAD RATING OF THE BUSHING. GREATER
lOADS MAY CAUSE BUSHING DAMAGE THAT COUlD
RESUlT IN SEvERE PERSONAl INJURY, DEATH, OR
PROPERTY DAMAGE.
Draw-ead bushings usuay require no maintenance
except as described on Page 20. Maintenance
instructions for condenser-type bushings are furnished
with the bushings.
low-votae BushinsTransformers are normay suppied with cast resin or
porceain draw-ead bushings. These bushings usuay
require no maintenance except as recommended on
Page 20.
Sure ArrestersTransformers may be furnished with optiona distribution
cass, intermediate cass, or station cass surge
arresters. Arresters are shipped separatey from the
transformer to preent damage. Upon deiery, unpack
the arresters and carefuy inspect them for damage,especiay the porceain components. Insta surge
arresters according to instruction found on Page 14.
19
RadiatorsTransformers are furnished with radiator assembies
(usuay pane type) to dissipate heat from the
transformer. Cooing fans may aso be furnished to
proide additiona oading capabiity without oerheating
the transformer. Radiator assembies may be shippedseparatey from the transformer to reduce the shipping
size of the transformer and to preent damage. When
radiators are shipped unattached, they shoud be
instaed in the ed according to the instructions on
Pages 11 and 12.
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DANgER: THE TRANSFORMER MUST BE
DE-ENERGIZED BEFORE BEGINNING ANY
MAINTENANCE WORK. FAIlURE TO DO SO COUlD
RESUlT IN SEvERE PERSONAl INJURY, DEATH, OR
PROPERTY DAMAGE.
It is the responsibiity of the owner to inspect, maintain,
and keep the transformer in proper operating condition.
Report a faiures during the warranty period to the
Howard Substation Transformer Diision. A warranty
repairs must be made or approed by the Howard
Substation Transformer Diision.
WARNINg: TANK lEAKS MUST BE REPAIREDIMMEDIATElY UPON DISCOvERY. FAIlURE TO
DO SO COUlD RESUlT IN SEvERE PERSONAl INJURY,
DEATH, OR PROPERTY DAMAGE.
Periodic Tests and InspectionsThe foowing periodic tests and inspections are
recommended for routine maintenance of the
transformer.
1. Gauge readings (one month after initia
energization and annuay thereafter). Gauge
readings, ambient temperature, and kvA
oad shoud be measured and recorded. Anyabnorma reading suggests that further
diagnostic testing or inspection shoud be
done. If pressure/acuum gauge and/or
uid ee gauge readings suggest a possibe
tank eak, perform a pressure test according
to instructions found on Page 14 (Pre-
energization Tests and Checklist). Tank eaks
must be repaired immediatey to preent serious
damage to the transformer and danger to ife.
2. Cooing fans (annua). Check the cooing fans
(if any) by setting the fan “auto/manua” contro
switch to the “manua” position. The fansshoud rotate at fu speed within approximatey
e seconds. The fans shoud rotate smoothy
with minima ibration.
3. Contro wiring (annua). Contro wiring shoud be
checked to insure that wire insuation is in good
condition. The contro cabinet and associated
conduit shoud be inspected to ensure that
weather seas are intact. Contro power suppy
otage shoud be checked and compared to the
otage stated on the wiring diagram.
4. Paint nish (annua). Inspect the paint nish for
damage or weathering that exposes the primer
coat or bare meta. Repair any paint damage
that might be found.
5. Fuid dieectric test (annua). Sampe the
insuating uid as described beow. The
dieectric strength of the insuating uid shoud
measure at east 26 kv.
6. Bushing and surge arrester insuators (annua).
Bushing and surge arrester insuators shoud be
cean. If the surfaces are excessiey dirty, they
shoud be ceaned whie the transformer is not
energized.
7. Bushing terminas (one month after initia
energization and annuay thereafter). If the
transformer is energized and under oad,
measure bushing termina temperatures
using an infrared scanner. Excessie bushing
termina temperature indicates a oose or dirty
connection. If the transformer is not energized,
use a torque measuring deice to make sure
termina connections are tight.
Sampin of Insuatin FuidTransformers are ed with insuating uid, which
proides eectrica insuation within the transformer
tank and transfers heat generated in the cois to thetank wa and radiators. The uid is either conentiona
transformer oi (minera oi), Enirotemp® FR3 uid, or
siicone uid.
Periodicay check the transformer for proper uid ee
by reading the uid ee gauge. Add uid if necessary.
When adding uid, add ony the same type uid that is in
the transformer.
It is aso recommended that a uid sampe be drawn
annuay and tested for dieectric strength. Sampes
shoud be drawn from the bottom of the tank. Use
proper samping procedures to preent erroneous test
resuts. Dieectric strength shoud measure 26 kv
minimum.
MAINTENANCE
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21
gasketsvisuay check a gaskets for cracking or other signs of
deterioration. Repace as necessary. When repacing
a gasket carefuy cean mating surfaces to remoe any
rust, dirt, transformer uid, od gasket materia, or other
contamination that might preent a good sea. Use anappropriate gasket cement when instaing new gaskets.
Do not reuse od gaskets. Six months after repacing a
gasket, check and retighten if necessary.
Additiona Maintenance InstructionsContact the Howard Substation Transformer Diision for
additiona maintenance instructions.
Repair PartsRepair parts can be ordered from the Howard Substation
Transformer Diision. A description of the part and the
transformer seria number wi be required to ensure thatthe correct part has been ordered.
Warranty CaimsThe Howard Substation Transformer Diision shoud
be notied immediatey when probems are discoered
during the warranty period. A warranty repairs must be
made or approed by the Howard Substation Transformer
Diision.
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NOTES
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Document 2.4.06, Reision 2December 2011 Medium Power Substation Transformers
Instructions for Instaation, Operation, and Maintenanceof Medium Power Substation Transformers
Document 2.4.06, Reision 2 (December 2011)
Copyright © 2011, Howard Industries, Inc.
laure, Mississippi
Teephone: 601-425-3151
Fax: 601-649-8090
Web: howardtransformers.com