trafo erection and commissioning
-
Upload
sandyarajagopalan321 -
Category
Documents
-
view
223 -
download
0
Transcript of trafo erection and commissioning
-
7/27/2019 trafo erection and commissioning
1/30
1. GENERAL
1. Introduction
The transformers are designed, manufactured and tested with care. With proper attention
during Installation and use, the user should receive from it the service, which he may reasonably
expect. The purpose of this Instruction Book is to explain how the transformer should be
installed, commissioned and maintained. The book is necessarily very general in character.
No transformer should have rated voltage applied to it until all the preliminary work and
checks described hereunder have been completed.
No high voltage tests should be made without making reference to the manufacture.
A transformer which has been commissioned and later withdrawn from service for any
considerable time should be re-checked as when first commissioned.
1.1 ARRANGEMENT FOR TRANSPORT
1.1.1 Transformers are thoroughly dried out before despatch. Oil, whether in the transformer
tank or in separate drums, is clean and dry when despatched.
1.1.2 Parts that are liable to be damaged in transit; are removed, packed and despatched in
separate leases. Radiators, bushings, explosion-vent/PRV dehydrating breathers, rollers and
buchholz relays. It always removed during despatch, wheather proof blanking plates being
provided where necessary. Transformers are despatched from the factory in either of the
following conditions:
a) With oil covering core and coils only
This is the usual arrangement wherever transport limitations permit. The tank is made oil
tight. Extra oil for filling up the tank, conservator and other fittings is sent in separate sealed
drums.
b) With no oil in the tank
The transformer is filled with nitrogen. The gas pressure and temperature at the time of
despatch from the factory are painted on the tank cover. Full quantity of oil is sent in separate
sealed drums.
1.2. INSPECTON
1.2.1 Before Despatch
The transformers are inspected and despatched from manufactirer works in first class
operating conditions, suitably packed for transport to destination.
1.2.2 At Site
1.2.2. External
A thorough external examination should always be made immediately on arrival at site.The various packages should be checked against the advice notes. Any discrepancies from the
advice notes should be immediately reported to the insurance underwriters, transporters under
intimation to supplier. In the event of outward damages, open delivery should be demanded
from transporters. Thereupon claims should be lodged with transporters and underwriters under
advice to supplier.
TRANSFORMER ERECTION & COMMISSIONING
267
-
7/27/2019 trafo erection and commissioning
2/30
1.2.2.2 Internal
An internal examination should be carried out to the maximum possible extent through
the inspection cover. The tightness of nuts and bolts should be particularly checked. Core and
coils should not be lifted unless there is reason to suspect internal damage.
1.2.3 Damage/Loss
1.2.3.1 Damage or loss of any component should be reported to supplier immediately. Photograph
or other useful evidence should be submitted where possible.
1.2.3.2 When the transformer is despatched filled with oil, a sample of oil should be taken from
the bottom of the tank and tested to I.S. 335. If the di-electric strength is below 40 kV BDV
when tested on a standard test gap as specified in I.S. 335, the matter should be reported to
supplier along with insulation resistance values of the various windings to earth.
1.2.3.3 Drums containing transformer oil which have been despatched separately should be
examined carefully for leaks or any signs of tampering. All drums are despatched filled up to
their capacity and any shortage should be reported. The drums should be stored in horizontal
(lying) position, with bung at 45 downwards.
1.2.4 Deterioration
1.2.4.1 The presence of rust or condensation anywhere within the tank indicates that moisture
is present. The transformer should not be energised until it has been dried out by the method
given in clause 2.5 of this booklet.
1.2.4.2 When transformers are despatched gas filled, the pressure and temperature, when
received at site, should be checked against the despatch pressure and temperature painted on
the tank cover. Pressure difference indicates that the seal is ineffective. If the pressure is the
same as the atmosphere, breathing may have taken place or the pressure may have gone down
because of temperature variations. In such a case the temperature of the transformer should
be raised above that of the 5urrounding air and a second measurement taken. If the internal
and atmospheric pressure are still the same, breathing is taking place and drying out may benecessary. This should be referred to supplier giving the pressure measured and the temperature
at which the measurements were taken.
1.3 HANDLING
1.3.1 Apart from the main lifting points designed to take the total weight of the unit, transformers
often have subsidiary lifting points suitable only for particular components. Care must be taken
to distinguish between them.
1.3.2 When lifting a tank, whether empty or with core, coils and oil, the cover must always be
bolted in position with the full complement of bolts.
1.3.3 Transformers should be jacked up using the projections specially provided for that purpose.
Jacks should never be placed under any valves
1.3.4 To avoid undue mechanical stresses the transformers must be kept on reasonably level
foundation.
1.3.5 Regarding oil please refer clause 2.3 of this booklet.
268
-
7/27/2019 trafo erection and commissioning
3/30
1.4 STORAGE
1.4.1 After arrival at site, it is desirable to erect and commission the transformer with minimum
delay. In Case this is not possible the transformer should be erected at its permanent location
with conservator and breather filled und dry oil filled to the correct level. Whether in storage or
in use, the dehydrating breather must be fitted on all transformers which are oil filled. The
breather incorporates an oil sealing device which must be filled with oil to the level marked to
be effective. The condition of silicagel must be checked periodically, particularly during monsoons.
The floating arm of the oil gauge on the conservator which is locked during despatch should be
released. The conservator and associated pipe work must be checked for rust or any foreign
matter and then flushed with dry oil before fitting. Breather inspection should be carried out.
Wherever possible, it is most desirable to keep the transformer energised even at a low voltage
so that the .oil temperature is about 10/150C higher than the surrounding ambient temperature.
1.4.2 All other accessories should be stored in a covered dry place. It should be ensured that
there is no damage to the gasketted joints and that all the blanked joints are tight.
1.4.3 Indoor type. transformers must be protect9d from the whether at all times. Outdoor
transformers may be stored outside, but it is preferable to store all transformers in a warm room
in which the temperature variation is small.
1.4.4 During the temporary storage, the tank should be kept on beams to enable free flow of air
underneath, unless the construction of the tank and base itself permits such a flow of air.
1.4.5 The tap changer, if provided, should be operated at 6 monthly intervals. Two or three
runs from one end of the range to the other and back are sufficient.
1.4.6 Heaters for marshalling kiosks, etc. should be kept energised. If, for this purpose, power
supply at the appropriate voltage to suit the heaters is not available, temporary heaters should
then be installed to suit the site voltage. The provision of heaters is important and failure to
provide them may result in extensive damage to the contents of the kiosk because of condensation.
1.4.7 All exposed paint work should be examined periodically. If any touching up is required. it
should be carried out as described under clause 2.22 of this booklet.
1.4.8 Parts despatched separately are generally packed in cases or crates, although certain
major items are sometimes despatched without packing. All items should be stored unreceived
in a dry and covered place provided there are no sign of damage or rough handling.
1.4.9 If oil received in drums is not likely to be used immediately the drums should be stored in
a covererd space where the temperature variation is minimum, If it is necessary to store the oil
outside, adequate protection must be provided at all times. Drums should not stand on end but
should be placed on their sides with the bung at 45 downwards.
269
-
7/27/2019 trafo erection and commissioning
4/30
Fig.2TypicalUnloadingArrangementoftheTransformer
270
-
7/27/2019 trafo erection and commissioning
5/30
2 INSTALLATION
2.1 PRECAUTIONS
2.1.1 Workmen having access to the interior of a transformer should empty their pockets of all
loose articles. Any spanners or other tools used should be securely tied with a tape so that
they can be recovered, if accidentally dropped.
2.1.2 Fibrous cleaning material should not be used. The presence of loose fibers in suspension
in transformer oil can reduce its insulating properties. If any cleaning or wiping is necessary,
this should be done with clean and dry oil, using soft-non fluffy cloth.
2.1.3 All components despatched separately should be cleaned inside and outside before being
fitted. Rusted internal surfaces should receive special attention.
2.1.4 Transformer oil is inflammable and, under certain circumstances in a confined space, may
become explosive. Naked lights and flames should never be used near a transformer.
2.1.5 Transformer oil and the cellulose-based solid insulations normally used in transformer
construction absorb moisture easily, particularly when cold. Condensation can be caused if the
interior of a tank is exposed to atmosphere. But by taking adequate precautions this can be
minimised.
2.1.6 Whether despatched with or without oil, a transformer is best protected, from damp
hazards by circulating warm, dry, deaerated oil through it until its temperature is 5C to 10C
above ambient. This should be done before allowing external access to the interior of the tank.
The warm oil should be circulated all the time the transformer is open to atmosphere.
2.1.7 Any air entering a transformer through leaky joints or with the oil may get lodged in
vulnerable places such as windings. To prevent this, the oil pump and all joints in the oil pipe
work should be air tight.
2.2 LOCATION AND SITE PREPARATION
2.2.1 No special foundation is necessary for the installation of a transformer except a level floor
strong enough to support the weight and prevent accumulation of water. Foundation incorporating
special oil drainage facilities during fire and emergency is strongly recommended for large
transformers.
2.2.2 Transformer should be placed on the foundation so that easy access is available all
around and diagram plates, thermometers, valves, oil guages, etc., can be easily reached or
read. Adequate electrical clearances are also to be provided from various five points of the
transformer to earthed parts.
2.2.3 Type ON transformers depend entirely upon the surrounding air for carrying away the
heat generated due to losses. For indoor installation, therefore, the room must be well ventilated
so that the heated air can escape readily and be replaced by cool air. Air inlets and outlets
should be of sufficient size and number to pass adequate air to cool the transformer. The inlets
should be as near the floor as possible and outlets as high as .the building will allow. Where
necessary, exhaust fans can be installed for the purpose.
2.2.4 The transformers should always be separated from one another and from all walls and
partitions to permit free circulation of air. In this connection reference is also drawn to clause
7.3 of I.S. 1886-1967.
271
-
7/27/2019 trafo erection and commissioning
6/30
2.2.5 Where rollers are not fitted, level concrete plinth with bearing plates of sufficient size and
strength can be adopted for outdoor transformers. To prevent the formation of rust, it is
essential to avoid presence of air and water in the space between the plinth and the base of
the transformer by use of cretex or similar bituminous compound.
2.2.6 Where rollers are fitted, suitable rails or tracks should be used and the wheels locked toprevent accidental movement of the transformer. Where walls are provided it should be ensure
that the transformer gets a good ventilation as mentioned above for indoor transformers.
Provision should be made for the emergency drainage of the oil from the transformers (e.g. in
case of fire in neighbouring apparatus or bushing or the transformer tank). by surrounding the
transformer plinth with sump filled with small pebbles.
2.3. Oil
2.3.1 When. Transformer oil is despatched to site separately. it is usually in sealed steel drums.
At the time of filling the drums it is ensured that the oil is filtered clean and dry.
2.3.2 If the drums are stored outdoors, they should be on their sides with the bungs downwards
at 45 to vertical.
2.3.3 Specification
The oil to be used for filling or topping up the transformers should be as per IS : 335 .
3.2.4 Precautions
2.3.4.1 Oil is easily contaminated. It is very important when sampling the oil and filling the tank,
to keep the oil free from contamination.
2.3.4.2 All equipment used for handling the oil should be cleaned and flushed with clean
transformer oil before use (the oil used for washing must be discarded). Particular attention
should be paid to the cleanliness of bungs, valves and other points where dirt or moisture tends
to collect.
2.3.4.3 For sampling, glass containers with glass stoppers are to be preferred over the metal
type which are susceptible to contamination by dirt. etc. Cleanliness is essential as even small
amounts of dirt and water will affect the accuracy of test results. Wax should not be used for
sealing the oil sample bottles, However, the stopper can be covered by a pack of silicagel tied
in a piece of cloth.
2.3.4.5 Flexible steel hose is recommended for handling insulating oil. Some kinds of synthetic
rubber or PVC hoses are also suitable but only those known to be satisfactory should be used.
Ordinary rubber, hose should not be used for this purpose as oil dissolves the sulphur from the
rubber and is thereby contaminated. Hose used for handling oil should be clean and free from
loose rust or scales.
2.3.4.6 Transformers must always be disconnected from the electricity supply system before
the oil level in the tank is lowered. .
2.3.4.7 Oil must not be emptied near naked lights as the vapour released is inflammable.
2.3.4.8 Minute quantities of moisture (particularly in the presence of fibres or dust) lower the
di-electric strength of the oil. To reduce the risk of condensation and moisture entering the oil.
containers taken into a warm room should not be opened until the entire body has attained the
same temperature as the room.
272
-
7/27/2019 trafo erection and commissioning
7/30
2.3.5 Sampling and Testing
Oil takes up moisture readily and its condition should always be checked before use. Oil
of a muddy colour is certain to be wet. Water and water saturated oil are both heavier than dry
oil and sink to the bottom of any container. Samples should therefore, be taken from the
bottom. Sample should not be taken unless the oil has been allowed to settle for 24 hours if
from a drum and for several days, if from a large transformer.
2.3.6 Samples from tank
Dirt from the draw-off valves or plug should be removed. To ensure that valve is clean,
some quantity of oil should be allowed to flow into a separate container before collecting
sample for testing. Samples should be collected in clear glass receptacles so that any water
present will settle at the bottom of the receptacles and will be clearly visible. Only glass bottles
with stoppers should be used for sampling.
2.3.7 Samples from drum
The drum should first be allowed to stand with bung vertically upwards for atleast 24
hours. The area around the bung should be cleaned. A clean glass or brass tube long enough toreach within 12 mm of the lowermost pmt of the drum should be inserted, keeping the uppermost
end of the tube sealed with the thumb whilst doing so. The thumb should be removed, allowing
oil to enter the bottom of the tube. The tube is to be resealed and an oil sample withdrawn.
The first two samples should be discarded. Thereafter the samples should be released into a
suitable receptacle.
2.4 PROCESSING OF OIL
In case when transformer is supplied with gas, it is customary to supply oil in drums. It
is not possible to filter each and every drum and test it before filling in transformer. It is
therefore necessary to have a container with suitable fittings so that the oil can be processed
to the required quality.
The figure 5 shows a typical arrangement of oil storage tank along with the fittingsrequired.
This storage vessel can be transported on a truck and can be lifted empty through the
lifting holes provided on the base channel.
2.4.1 Oil Filling of Transformer Tank
Before filling oil in the tank, it should be tested to meet the following requirements:
BDV PPM
(i) For transformers upto 132 kv class 60 kv 15
(ii) For transformers above 132 kv class 70 kv 10
In case the oil does not meet the requirements, it should be processed and should only
be used when it meets the requirements. For transformers despatched gas filled, the filling of oil
inside the tank should be done under vacuum. Transformers of high voltage ratings have their
tanks designed to withstand partial or full vacuum. The safe vacuum as consistent with the
tank design should be used for filling the oil. When filling a transformer with oil, it is preferable
that the oil is pumped from the bottom of the tank and that a filter press or other reliable oil
drying and cleaning device is interposed between the pump and the tank. If the maximum
suitable vacuum is maintained in the interior whilst oil is being pumped in, the hazard of bubbles
lodging in inaccessible corners of winding is very much reduced. Any air that remains will
273
-
7/27/2019 trafo erection and commissioning
8/30
dissolve in the partially ceaerated oil when the vacuum is broken. It should also be ensured that
the tap changer board, condenser bushing, relief vent diaphragm, buchholz relay, conservator,
etc., are not subjected to full vacuum as they are not designed for the same.
2.5 DRYING OF TRANSFORMERS
2.5.1 The process of drying out a transformer is one requiring care and good judgement. If the
drying out process is improperly performed, great damage may result to the transformer insulation
through overheating, etc. A properly dried out and correctly installed transformer is one of the
most reliable electrical appliances.
2.5.2 In no case should a transformer be left unattended during any part of the dry out period.
Transformer should be carefully watched throughout the dry out process and all observations
carefully recorded.
2.5.3 Drying of core and coils using oven
2.5.3.1 Where a suitable oven is available the core and coifs can be effectively dried in it by
raising the temperature to a level not exceeding 80C. This applies to oil-soaked transformers
also. A large volume of air should pass through the oven to remove moisture and vapour. Aninsulation resistance check will indicate when the coils are dry. The speed at which air impinges
on the core and coils must not exceed 600 metres per minute. The oil, in which the dry core
and coils will subsequently be immersed, must be processed and must meet the requirements la
ill down in clause 2.3.1.
2.5.3.2 An alternative method can be used where transformer is to keep the core and coils in
its own tank in an oven. This method can be used where the tanks are designed for full
vacuum. The vacuum will be drawn from the top of the tank by connecting a suitable pump to
any valve fitted at the top of the tank. The temperature in the interior of the tank should not
exceed 75C. Care should be taken that the heating and application of vacuum should be
alternated in sequence. Dry nitrogen gas should be used whenever vacuum is required to be
broken.
2.5.4 Drying out a transformer using Streamline filter machine
2.5.4.1 The most practical method of drying out is by circulation of hot oil through a Streamline
filter machine incorporating oil heater and vacuum chamber (or other oil cleaning and moisture
removing device). Before using any filter machine it should be ensured that any other oil filled in
the filter machine is first drained and refilled with oil supplied along with the transformer. The oil
should be circulated through the filter machine several times and oil sample should be tested. If
test results are in order, the filter machine can then be used for circulating the oil through
transformer. The vacuum pump of the filter machine should have the capacity of creating
vacuum as high as possible, but not less than 710 mm of Mercury. Where possible a vacuum
pump can be connected to the top tank cover to keep the oil in tar1k under vacuum consistent
with tank suitability. This may speed up the drying out process. It is preferable to lag or blanketthe transformer tank to prevent loss of heat. To start with, oil is drawn from the bottom and let
into the transformer at the top. This will remove any settled moisture/impurities. After about 8
to 12 hours circulation in this manner, the cycle is reversed i.e., oil is drawn from the top and
fed at the bottom.
274
-
7/27/2019 trafo erection and commissioning
9/30
2.5.4.2 The oil temperature as measured by the oil temperature indicator should be of the order
of 75C it should be seen that the oil temperature at the filter machine in no case exceeds
85C. The circulation should be continued till the insulation resistance and oil samples taken
from various points test satisfactorily.
2.5.4.3 The IR values taken at regular intervals should be plotted against temperature readings.It will be observed that, in the beginning, IR values drop down as the temperature goes up. The
IR values will be low till moisture is present inside. Once the moisture is removed, the IR values
will start rising and then become steady.
CURVE SHOWING VARIATION OF INSULATION
RESISTANCE WITH TIME OF DRYING
Fig.3 Curve Showing Variation of Insluation resistance with time of drying
275
-
7/27/2019 trafo erection and commissioning
10/30
IR-TEMPERATURE CURVE
Fig.4 IR - Temperature Curve
2.5.4.4 If necessary equipment is available, the power factor reading can be taken, which gives
a reliable check on the condition of the solid insulation in a transformer. Capacitive power factorangle is different for each transformer design and the factory tested figure at a suitable
reference temperature can be made available to the user, on request at the order stage.
2.5.4.5 The transformer can also be heated up by short circuiting the low voltage wind inn andsupplying a reduced voltage at high voltage terminals. The supply voltage should be maintainedin such a way that the current in the windings does not exceed 70% of normal full load currentand the oil temperature, as mentioned above, is about 75C. In this case, temperature of oilshould be measured at the bottom of the tank also. Constant watch is to be kept to ensurethat the temperature limits are not exceeded. The temperature of the windings which can be
measured by the following formula should in no case exceed 90C.
R2 (235 + T1)-235
T2 = ----
R1Where T2 = final average temperature of the copper.
T1 = Initial temperature of the copper.
R2 = Final resistance of the windings.
R1 = Initial resistance of winding.
This method is more effective in drying the insulation but requires care und supervision
of an experienced engineer.
276
-
7/27/2019 trafo erection and commissioning
11/30
Fig.
5
277
-
7/27/2019 trafo erection and commissioning
12/30
2.5.4.6 IR Temperature relation
It has always been the question from our customers as to how the IR value can be
converted at different temperature. We have drawn a curve (fig. 4) for guidance of the
operating staff on the basis of our experience, so that they can judge the IR Value at any
temperature. This curve cannot be taken for absolute value but will serve as a good guide forconversions of IR values at different temperatures. A simple example is given as to how to
calculate the value at different temperatures. Suppose IR value at 70C is 300 M. Ohms and
we want to convert at 40C, the curve will give you a factor K for difference in temperature i.e.
(70 - 40) = 30C
K for 30C temperature difference = 4.2
So the value at 400C = 4.2 x300 = 1260 M. Ohms. Value thus converted fairly tally with
the actual value when cooling the transformer. The factors are tabulated as below:
Difference 10 20 30 40 50in temp. ( C)
Factor K 1.65 2.6 4.2 6.6 10.5
2.6 GASKETS AND GASKET JOINTS
2.6.1 Transformer gaskets are of neoprene bonded cork and when supplied loose, have no bolt
holes in them. They are usually cut to the size and shape required, although they may be
supplied as straight, angled, or in U-shaped pieces from which complete gaskets can be built
up.
2.6.2 Only scared joints should be used i.e. a 40 mm scarf in 5 mm thick material is recommended.Joints should be located away from corners and bolt halos, and should be well bonded smooth
and free from local thickening, Neoprene solution is used as an adhesive for joints.
2.6.3 Gaskets are best stored in hermetically sealed containers in a cool place. They must be
protected from damp, oil and grease.
2.6.4 To make a gasket joint first clean the metal surfaces ensuring that they are free from oil,
rust, scale, etc. Using one of the flanges as a template, punch the necessary bolt holes. Insert
the bolts and tighten the bolts sequentially, a little every time so that uniform pressure is
exerted on the gasket until the gasket is compressed to about 2/3 of its original thickness.
Joints should not be subjected to pressure until tightening is complete. If care is taken inmaking joints, and in handling the gasket, it is possible to break and re-make a joint several
times, using the same gasket.
278
-
7/27/2019 trafo erection and commissioning
13/30
279
-
7/27/2019 trafo erection and commissioning
14/30
2.6.5 For making leak proof and good gasket joints, it is necessary that uniform pressure is
achieved all over the gasket after mating rims/flanges have boon clamped with bolts/studs.
Following instructions be followed for proper tightening of bolts/studs.
(i) Tighten lightly the bolts/studs diagonally in the sequence as shown in the figure given
below:
Fig. 7
(ii) Tighten again bolts /studs in the same sequence with full pressure till gasket thickness isreduced to 2/3 of original thickness.
(iii) Do not overtighten otherwise gasket will get crushed.
2.7 BUSHINGS
2.7.1 Bushings are usually removed for transport and the bushing holes blanked off. Before
fitting, bushing should be examined for damage or cracks which may have occurred during
transit. They should be cleaned with a dry non-fluffy cloth. Bushings are normally despatched
fully assembled and filled to the correct level with the appropriate filling medium. Where a fluid
filling is used, a check of the level must be made and the bushing filled up to the correct level,
if necessary. Any leakage should be checked and stopped before the bushing is fitted.
2.7.2 Bushings should be assembled with their adaptors. if supplied, using the proper gaskets
for the various joints. When clamping the bushings to the tank, care should be taken to ensure
that an even pressure is obtained on the flange of the porcelain and its gasket by tightening
the diagonally opposite nuts alternatively. The line connections to all types of bushings should
be flexible to ensure that there is no strain exerted on the bushings because of line movement
such as swing, expansion. contraction. etc. If arcing horns are fitted, the gaps should be
carefully checked and reset to the values shown on the outline drawing or give in the instruction
book supplied along with the transformer.
For condenser bushing, please refer separate leaflet.
2.8 CABLE BOX
2.8.1 The laying of cables, connecting up and filling the cable boxes are usually the responsibility
of the cable contractor and as such have not been dealt with here.2.8.2 The cable box should be filled to the correct level with suitable filling medium (I S : 7084
class III) before energizing. lf the transformer is delivered to site with the cable box detached,
this should be assembled on the transformer before filling with compound and allowed to stand
with full oil head behind it for 24 hours. This is to check against possible oil leaks into the
compound.
280
-
7/27/2019 trafo erection and commissioning
15/30
Fig. 9
281
-
7/27/2019 trafo erection and commissioning
16/30
2.8.3 The cables should be supported separately to ensure that no undue strain is exerted onthe porcelain terminals in the cable box. The filling holes should be made weatherproof.2.8.4 Hot compound should never be poured directly on the porcelain of insulator.
2.9 CONSERVATOR
2.9.1 As the temperature of the transformer oil increases or decreases, there is a correspondingrise or fall in the oil volume. To account for this. an expansion vessel (conservator) is connectedto the transformer tank.2.9.2 Conservator, where fitted. should be assembled with its pipe work. etc., making sure thatall gasket joints ,He oil-tight and the pipe work is clean and free from moisture. The mechanismof the float type oil gauge inside the conservator is locked to prevent damage during transit.After placing the conservator in position, it should be released by turning the locking bolt in thedirection indicated on the plate.2.9.3 While topping up oil in the transformer. it should be ensured that oil is filled to the levelindicated by the oil gauge on the conservator and commensurate with the oil temperature atthat lime.
2.10 SILICAGEL DEHYDRATING BREATHERSSilicagel breaths arc despatched as loose items to prevent silicagel getting wet by oil in
the breather cup. The plug sealing the top of the breather should be removed and connectedto the associated pipe work. The oil cap at the bottom of the breather should be removed filledto the mark on the inside wall with transformer oil and the cap replaced. The oil seal ensuresthat silicagel is prevented from absorbing moisture when the transformer is not breathing (referto separate leaflet on breathers).
2.11 EXPLOSION VENT2.11.1 A temporary cover is provided over the explosion vent flange on the tank cover. Thisshould be removed and the explosion vent fitted with suitable gaskets, care being taken toensure that the top diaphragm with its gaskets makes on air tight joint. The explosion vent issent blanked from works and the top blanking plate should not be removed till the oil level inside
the transformer comes above the tank cover.2.11.2 Where a transformer is provided with a buchholz device, a bottom paper diaphragmwhich acts as deflector plate, is fitted at the base of the explosion vent to ensure that anygases liberated in the transformer will pass through the buchholz relay and not collect in thevent. A hole in the side permits the oil to enter the vent and equalise the pressure on either
side of the deflector diaphragm.
Arrangement of Explosion Vent
Fig. 9
282
-
7/27/2019 trafo erection and commissioning
17/30
2.11,3 In transformers of large ratings the space above the oil in the vent is usually connected
by n pipe to the top conservator to equalise the pressure and vent it to tip. atmosphere
through the breather. For transformers supplied without equalising pipe an air-cock is fitted at
the top which must be opened when the tank is being filled with oil and closed again.
2.12 PRESSURE RELIEF VALVE
In some of the temperature where explosion vent is not provided, Pressure Relief valve
is provided. Pressure relief valves are usually removed for transport and the mounting holes on
the transformer tank over blanked off. Examine the valve for damages, if any, before mounting.
Check the continuity of contacts with Avometer. The flag operation should be checked manually
by lifting the switch operating rod.
The following checks should be observed before installation of Pressure Relief Valve on
the transformers:
(1) Use gasket supplied along with the valve.
(2) Before P. R. V. put to service each valve should be cleaned with compressed air.
The rubber gasket supplied with the valve should be cleaned and located properly in the
recess carefully. All the bolts should be tightened evenly and sequentially so that equal pressureis exerted on gasket and base. The details of the pressure relief valve are as per figure no. 8
2.13 BUCHHOLZ RELAY
2.13.1 The buchholz relay is connected in the oil pipe work between the transformer tank and
the conservator: It a valve is fitted to isolate the conservator, the buchholz relay is usually on
the transformer tank side of the valve. The buchholz relay should be mounted in the pipe work
only alter oil level inside the transformer is above the tank cover.
2.13.2 To ensure successful operation of the relay, the pipe work on either side of the relay and
the relay itself, are all set at the same angle (3 - 7 to the horizontal for double float relay). A
machined surface is provided on the housing of the relay to check the level. The arrow on the
housing should point towards the conservator. The gas release pipe, when provided, is connected
to the top petcock of the buehholz relay. In service, the top petcock should be kept open and
the gas release pipe should be full of oil. When the gas is to be collected through the gas
release pipe oil will flow out initially followed by the gas.
Conservator tank oil pipe work showing the
portion of buchholz protection
Fig. 10
283
-
7/27/2019 trafo erection and commissioning
18/30
2.13.3 Before putting the transformer into service. all air which may have collected in the relay
should be allowed to escape through the top petcock. The alarm and trip terminals are clearly
marked for function and polarity. When making the connection from these terminals in conduits.
care must be taken that condensate should not drain into the terminal box. For details refer
separate booklet on buchholz relay.
2.14 TEMPERATURE INDICATORS
2.14.1 Oil temperature and winding temperature indicators operate on the principle of liquid
expansion and provide local indication of top oil and winding hot spot temperature respectively
at the marshalling kiosk. The thermometer bulb is connected by capillary tubing to the local
indicator. The bulb is enclosed in a pocket which is normally fixed in the transformer cover in the
hottest oil region. The oil temperature and winding temperature indicators are provided with a
maximum pointer and mercury switches as required by the customer. The oil temperature
indicator is the same as the winding temperature indicator except for the CT circuit and heating
element on the pocket.
2.14.2 In the case of WTI of the Heated Bellows type, heating element is incorporated in theinstrument itself. thus eliminating the heating element in the pocket.
2.14.3 The steel capillary tube is protected by a copper tubing which is strong enough to
withstand normal handling. It should not, however be bent sharply or repeatedly and should be
supported by clips to prevent sagging. On no account should it be cut. The thermometer
pockets for OTI and WT/ should be filled with transformer oil,
2.14.4 Normally winding temperature indicator is provided on one phase of the LV winding.
Where required, WTI can also be provided on the HV winding and also on different phases.
2.14 5 Before installing. the accuracy of the instrument snou1d be checked by hot oil or water
both. The mercury switches are adjusted to make contact at the desired temperatures depending
upon site conditions i.e., ambient temperature, loading condition, etc.
214.6 The CT connection of the WTI is made to the thermometer pocket as per instructions
given on the WTI terminal board. For details. refer separate book let on temperature controller.
2.15 COOLING EQUIPMENT
2.15.1 Radiators
Individual radiator, pipe work and headers should be cleaned and flushed with clean dry
oil before fitting. These should be assembled as shown in the outline drawing. The radiators
should then be filled with...clean and dry transformer oil. Air should be release from top of the
header and also from each radiator.
The inter-connecting valves between the tank and radiators are opened only when dry
out is completed.2.15.2 The fans and pumps should be wired to the respective terminals in the marshalling kiosk
and the direction of rotation should be checked. For details of pumps refer separate booklet.
2.15.3 OFW Coolers: Please refer separate booklet on OFW coolers.
284
-
7/27/2019 trafo erection and commissioning
19/30
2.16 ON-LOAD TAP CHANGER
2.16.1 The tap changer, if despatched separately, is to be fitted onto the tank. The insulation
resistance value of each tap changer lead to earth should be measured and the cause of low
values, if any, investigated. The leads from the tap changer should then be connected to their
respective positions on the terminal board provided on the tank. The tightness of all connections
on the selector switch and terminal board should be ensured, Any protective taping on the
diverter switch bushing is to be removed.
2.16.2 It is advisable to fit the tap changer on the transformer even during storage and
connect it to the conservator and breather.
2.16.3 In some cases, it may be difficult to get good IR values if there is moisture in the tap
changer terminal board or on any of the parts of the selector switch and diverter switch. It
should, therefore, be ensured that the selector switch and diverter switch are filled with clean
dry processed oil. To remove moisture from the terminal board, it will be preferable to circulate
the oil in the selector switch tank and the main transformer tank simultaneously and at as high
a temperature as permissible. If some other special instructions are provided, the same should
be followed.
2.16.4 For internally mounted (type MR) tap changer please refer separate booklet.
2.17 OFF CIRCUIT TAP SWITCH
Before changing taps on transformers designed for off circuit tap changing, isolate the
transformer from supply on all windings. It is to be noted that tap change is complete only
when the tap switch handle completes one full revolution. To prevent damage due to inadvertent
operation, the tap switch handle should never be left halfway and/or unlocked.
2.18 CURRENT TRANSFORMERS
All CT secondary terminals should be short-circuited or loaded before energising the
transformer. This will prevent excessive voltages developing across the CT secondary whichcan damage the CT and be a hazard if touched.
2.19 EARTHING
2.19.1 The tank should be permanently and effectively earthed by means of connections to the
earthing terminals provided for the purpose at the bottom of the tank. (Refer Indian Electricity
Rules for details on earthing).
2.19.2 A good low-resistance earth is essential for adequate protection. The earthing connection
should be of sufficient cross-section to carry the l V line current for 30 seconds. Stabilising
winding, if supplied, for the suppression of harmonics, should have one point earthed to prevent
it from developing a high potential. Other accessories such as fan motors, oil pump motors,
etc., should be also earthed.
2.20 PAINT WORK
2.20.1 All metal parts are given three coats of high quality paint before despatch from the
works. The first, which is applied to the clean metal surface, is a primary coat, followed by an
intermediate coat and a final finishing coat. which is normally dark grey to shade no. 632 of 1.5.
5 or B.S. 381C unless specified differently by the purchaser. If the point work has been
damaged during or erection, touching-up should be carried au with tl1o least delay.
285
-
7/27/2019 trafo erection and commissioning
20/30
2.20.2 The following paints which are available from our approved suppliers should be used.
FIRST AND SECOND COATS OF PRIMER
THIRD AND FINISHING COATS
2.20.3 It the recommended paints are not available. a high Quality alkyd resin-based paint may
be used. The surfaces to be repainted should be clean and free from grease and rust. If rust
has begun to form; the surrounding area should also be cleaned, thoroughly as rust tends to
spread beneath paint work.
2.20.4 Failure to maintain the paint work in good condition will result in considerable deterioration
of the apparatus during storage or service.
2.21 TOPPING UP OF OIL IN TRANSFORMER
After completing mounting of all fittings on the transformer. the transformer should be
topped up with clean and dry oil meeting the requirements as given in clause 2,3.3 through thebottom filter valve with the help of a filter machine. Care should be taken to keep all air releaseplugs and valves open to allow escape of trapped air. The filling is to be continued till theappropriate level, indicated on the conservator corresponding to the oil temperature, is reached.The filling should then be stopped and air release plugs and valves should be closed.
Sl.No. Supplier Name Reference
1
2
3
4
5
6
Asian Paints
Addisons
British Paints
Alkali Chemicals
Garware Paints
Goodlass Nerolac
32 / F 3257
LS 2907
BPL Red Oxide Zinc chromatePrimer
32 781
RR 4460
205 /023
1
2
3
4
5
6
Shalimar
Goodlass Nerolac
Asian Paints
Jenson & Nicholson
Alkali Chemicals
British Paints
Superlac Synthetic Enemel
500 / 850
Apcolite Synthetic Enamel
Robbialac Superlac
Deluxe Synthetic Enamel
LUXOL 3 HIGLOSS Synthetic Enamel
286
-
7/27/2019 trafo erection and commissioning
21/30
2.22 COMPLETION OF ERECTION WORKS
Any other work such as wiring of various alarm/trip contacts from various accessories of
the transformer to marshalling kiosk. settings of relays, checking of protection scheme, etc.,
should be completed before the transformer is cleared for commissioning,
2.23 PARALLEL OPERATION
2.23.1 If it is desired to parallel a transformer which is not identical in design with BHEL
transformer, it is preferable to refer the matter to BHEL for advice.
2.23.2 The voltage ratios and impedance values at all taps should match for the two transformers
that are to be paralleled. Only certain combinations of vector groups are capable of being
paralleled. The table below indicates the more common permissible combinations.
2.23.3 Reference to the connection diagrams of two transformers should indicate the terminals
to be paralleled.
2.23.4 The reversal of two leads on either side of a three-phase transformer will reverse the
polarity. Changing them in sequence (e. g. from A. B. C. to B.C.A. or C.A.B.) will swing thevectors through 1200
2.23.5 Phase sequence and polarity can be checked by energising both transformers on the
primary side before paralleling, and measuring the open-circuit voltage appearing across each
pair of terminals which will ultimately be paralleled.
TRANSFORMER (B)
HV Delta Star Delta Star
LV Delta Star Delta Star
H.V./L.V.
Delta / Star Yes Yes No No
TRANSFORMER (A) Star / Delta Yes Yes No No
Delta / Star No No Yes Yes
Star / Delta No No No Yes
3. COMMISSIONING
3.1 After the transformer is installed in accordance with Section 2 undernoted
precommissioning tests and checks on instruments should be done before putting the transformerin service.
3.2 DRY OUT TEST
3.2.1 IR values of various windings to earth should be checked. While checking these values;
no external lines. lightning arrestors, etc., should be in circuit. Bushings should be throroughly
cleaned with a dry clean piece of cloth before taking I R values. The IR values obtained should
287
-
7/27/2019 trafo erection and commissioning
22/30
be comparable with those indicated in BHEI test report. In humid weather condensation on the
sheds can affect IR values.
3.2.2 After filling the oil in the transformer, it will again be re-conditioned as per cl. no 2.4 till
the following characteristics are obtained:
BDV PPM(i) For transformer upto 132 kV 50 kV 15
(ii) For transfollllP.r above 132 kV 60 kV 10
3.3 RESISTANCE MEASUREMENT OF WINDINGS
Winding resistance should be measured at all tap positions.
3.4 RATIO TEST
Ratio test between HV and LV at all taps should be carried out. For 3 winding transformers
ratio between other pairs of windings should also be taken.
3.5 PHASE RELATIONSHIP TEST
Test for verification of phase relationship and vector group should be conducted at site.
3.6 TAP CHANGER TEST
a) Manual operation.
b) Local electrical operation.
c) Remote electrical operation
d) Parallel operation.
e) The operations should be checked from one end of the range to the other to check for
limit switch operations also.
f) IR values of motor and control wiring should be checked with 500 V megger.
3.7 BUCHHOLZ RELAY TEST
Buchholz relay operation for alarm and trip should be checked by injecting air through
the test petcock.
3.8 LOW OIL LEVEL ALARM
The low oil level alarm of the oil gauge should be checked.
3.9 TEMPERATURE INDICATORS
The contacts of OTI and WTI for alarm, trip and control (where provided) should be
checked and set at required temperature.
3.10 COOLING GEAR TEST
a) The IR values and settings for operation of oil pump and fan motors should be checked.b) Alarm trip contact settings of differential pressure gauge, oil and water flow indicators,
where provided, should be checked.
3.11 MARSHALLING KIOSK
The wiring from various accessories to marshalling kiosk should be checked.
288
-
7/27/2019 trafo erection and commissioning
23/30
3.12 PROTECTIVE RELAYS
Tripping of the associated breakers is to be proved b actual operation of the differential
relay, over current relay, earth fault relay and other protective relays as applicable.
3.13 MAGNETISING CURRENT
The magnetising current can be measured by feeding 400 V. 3 phase, 50 Hz supply from
HV side keeping LV side open circuited and the values in different phases could be compared.
3.14 ADDITIONAL CHECKS
Checks should be made to see if :
a) All oil valves are in correct position closed or opened as required.
b) All air pockets are cleared.
c) Thermometer pockets me filled with oil.
d) Oil is at correct level in the bushings, conservator diverter switch. tank, etc.
e) Earthing connections are made.
f) Colour of silicagel is blue.
g) Bushing arcing horn gap is set correctly.h) CT polarity is correct (when bushing mounted CTs are provided).
If all the above tests/checks are found satisfactory a setting time of atleast 24 hours
should be allowed for the oil and air released from all points at 6 hourly intervals, before
commissioning the transformer. Wherever possible, while commissioning, the voltage should be
built up slowly and brought to the full level in about 4 to G hours. If the breaker is tripped on
differential. buchholz or any other device. the cause must be investigated before re-energising
the transformer. Sometimes tripping may be because of magnetic inrush which depends upon
the switching at a particular moment in the cycle. After commissioning magnetising current
should be measured by connecting with a meter in metering CT circuit and the reading should
be compared with the test report value.
4. MAINTENANCE
4.1 If a transformer is to give long and trouble -free service, it should receive a reasonable
amount of attention and maintenance. Mi1intenance consists of regular inspection, testing and
reconditioning where necessary. Records should be kept giving details of any unusual occurrence
and also of any test results taken.
The principal object of maintenance is to maintain the insulation in good condition.
Moisture, dirt the excessive heat are the main causes of insulation deterioration and avoidance
of these will, in general, keep the insulation in good condition.
No work should be done on tiny transformer unless it is disconnected from all external circuits
and all windings have been solidly earthed.
Note: The general notes and information given under storage, handling and installation etc. are
also applicable to routine maintenance.
4.2 TRANSFORMER OIL
Oil is used as a coolent and di-electric in the transformer and keeping it in good condition
will assist in preventing deterioration of the insulation which is immersed in it.
The peremissible limits of various characteristics as per IEC : 422 are given as per
Appendix A1 and A2 at the end.
289
-
7/27/2019 trafo erection and commissioning
24/30
A few short notes on the subject are given below
a) The oil level should be checked at frequent intervals and any excessive leakage of oil
investigated. There may be a slight loss of oil by evaporation; this need not cause
concern if the tank is topped up at regular intervals.
b) All minor leaks or seepages should be repaired as quickly as possible.
4.3 CORE & WINDINGS
It is recommended that the core and windings be removed from the tank for visual
inspection as per time schedule given in clause 4.17. The windings should be examined to
ensure that no sludge has been deposited blocking the oil ducts Any loose nuts and bolts
should be tightened.
Before lifting the core and windings from the tank it is usually necessary to disconnect
the windings from the bushings or cable boxes inside the tank, to disconnect the off-circuit tap
switch handle or leads of the on-land tap changer and to remove any earthing strips between
the core and the tank. The core and windings must be removed with great care, under cover
and in a dry place.
4.4 TAP CHANGER
See separate instruction booklet.
4.5 BUSHINGS
Porcelain insulators and rain sheds should be cleaned at convenient intervals when the
transformer is out of service. A metal pan scrubber can be used effectively to remove grime.
During cleaning, the porcelain should be examined for cracks or other defects and defective
ones replaced. Oil level in oil filled bushings should be checked at frequent intervals. The cause
of any serious loss of oil should be investigated. For details See separate maintenance booklet
on Bushings.
4.6 CABLE BOXES
The sealing arrangement for fillings holes should be chucked each year. When screwed
plugs are sealed with a bituminous compound, the compound should be exnll1irwd for cracks. If
the compound has cracked, it should be replaced as the cracks may lead to an accumulation of
water around the plug. Gasket joints should be examined and tightened.
4.7 COOLING EQUIPMENT
Please refer separate booklet.
4.8 CONSERVATOR
Conservators are so arranged that the lower part acts as a sump in which any impuritiesentering the conservator will collect. A valve is fitted at the lowest point of the conservator for
dri1ining and sampling. When sampling, care must be taken to run off any contaminated oil
before taking a sample for testing. The inside of the conservator should be cleaned as per
clause 4.17. A removable end is provided on each conservator for this purpose.
4.9 OIL GAUGES
Oil gauge glasses should be kept clean so that the gauges can fulfil their purpose.
290
-
7/27/2019 trafo erection and commissioning
25/30
Broken glasses should be replaced immediately; The gauges are normally fitted with armour
plate glass which is unbreakable under normal service conditions. When the conservator is
stripped for cleaning, the mechanism of the float type oil gauge, if fitted, should be inspected
and cleaned.
4.10 DEHYDRATING BREATHER
Breathers when fitted should be examined to ascertain if the silicagel requires changing.
The frequency of inspection depends upon local climate and operating conditions. More frequent
inspections are needed when the climate is humid and when the transformer is subject to
fluctuating load. The crystals of silicagel in the breather are tinted to act as an indicator and
change from blue to pink on becoming saturated with moisture. When the majority of the
crystals have turned pink, the silicagel should be replaced or reactivated. To reactivate the
gel, the crystals should be heated in a shallow pan at a temperature of 1500 C to 200C until
the original blue colour is regained. This usually takes 2 to 3 hours. The oil level in the oil seal
should be maintained up to the level indicated in the cup. (For full particulars see instruction
booklet on breathers.
4.11 BUCHHOLZ PROTECTOR
Routine operation and mechanical inspection test should be carried out as per clause 4.17. The
operation is tested by injecting air into the protector through the air injecting pipe. After
inspection, any air which has accumulated in the gas chamber must be released through the
upper petcock leaving the chamber full of oil.
To carry out mechanical inspection, the oil level should first be brought below the level
of protector and the mechanism removed. The floats should be able to rise and fall freely, and
the mercury switches should be tightly clamped and he in good order. If a switch is defective
swing to the glass being cracked there will be clouding of the glass. In such cases the switch
must be replaced, During operation, if there is an alarm and gas is found to be collecting, the
transformer should be isolated and the gas should be tested and analysed to find out thenature of fault. Sometimes it may be noticed that the gas collected is only air. The reasons for
this may be that the oil is releasing any absorbed air due to change in temperature or due to
leakage on the suction side of the pump. The absorbed air is released normally when no vaccum
is applied during filling of oil and also in the initial stages only. The internal faults can be
identified to a great extent by a chemical analysis of gas.
Buchholz may also give alarm/trip duo to oil level falling below the buchholz level.
Also see separate leaflet of the buchholz relays.
4.12 EXPLOSION VENT
The diaphragm, which is fitted at the exposed end of the vent, should be inspected at
frequent intervals and replaced. if damaged. Failure to replace the diaphragm quickly move
allow the ingress of moisture which, will contaminate the oil. If the diaphragm has broken
because of a fault in the transformer, an inspection should be carried out to determine the
nature and cause of the fault.
4.13 GASKETS
Gaskets sometimes shrink during service. It is therefore, necessary to check the tightness
of all bolts fastening the gasket joints. The bolts should be tightened evenly around the joints
291
-
7/27/2019 trafo erection and commissioning
26/30
to avoid uneven pressure. Leaking gaskets should be replaced as soon as the circumstances
permits.
4.14 SMALL PIPE WORK
The pipe work should be inspected atleast once a year leaks may be due to slackunions, which should be tightened, or due to badly seated joints caused by a misalignment. In
the latter case, the pipes should be aligned and joints remade.
4.15 TEMPERATURE INDICATORS
At each yearly maintenance inspection, the level of oil in the pockets holding thermometer
bulbs should be chucked and the oil replenished if required. The capillary tubing should be
fastened down again if it has become loose. Dial-glasses should be kept clear and, if broken,
replaced as soon as possible to prevent damage to the instrument. Temperature indicators if
found to be reading incorrectly, should be calibrated with standard thermometer immersed in
hot oil bath.
4.16 PAINT WORK
During storage and service the paint work should be inspected once a year and, where
necessary, painting or retouching carried out. If the metal surface is exposed and becomes
dirty, rusty or greasy because of delay in repairing the paint work, the surface must be
thoroughly cleaned before repainting to ensure a good bond between metal and paint. If paints
recommended by supplier are not available, any good quality alkyd resin-based paint may be
used.
4.17 MAINTENANCE SCHEDULE
The maintenance schedule given at Table-A is a good indication 01 the attention required
to be given to the transformer under average conditions.
292
-
7/27/2019 trafo erection and commissioning
27/30
S.No. Items to beinspected
Inspection notes Action required
HOURLYAmbient temperature -- --
Winding temperature
Oil temperature
Check that temperaturerise is reasonable.
Shutdown the transformerand investigate, if either ispersistently higher thannormal.
Load amps
Load voltage
Check against ratedfigures.
An improper tap position cancause excessive core loss.Voltage and tap position
should be corrected.
DAILY
Relief ventCheck the relief ventdiaphragm to be intact.
Investigate, replace if foundbroken.
Oil level intransformerconservator
Check oil level from oil
gauge.
Top up, if found low.
Oil level in tapchanger diverterswitch.
Check oil level from thegauge glass
Top up, if found low.
Oil level in bushings.Check the oil level fromgauge glass.
Top up, if found low.
Pipework andaccessories forleakages
Inspect the transformerfor leakages.
If leakages are observed,tighten evenly the gasketjoints. Replace 'O' ring orwasher suitably. Replace
gasket if needed.
Dehydrating breatherCheck colour of silicagel. Reactivate/replace with new
charge, if found pink.
Leakages of water intocooler
-- Investigate and rectify aftertaking shutdown.
MONTHLY
Bushings
Examine for dirtdeposition and tightnessof oil filling plugs,Examine for cracks inporcelain.
Clean and tighten plugs.Cracked porcelain should berectified/ replaced.
Transformer oil andtap changer oil
Check for di-electric
strength and moisturecontent.
Take suitable action to
restore quality of oil.
293
TABLE-A
-
7/27/2019 trafo erection and commissioning
28/30
S.No. Items to beinspected
Inspection notes
QUARTERLY
Cooler fan, bearingand controls
Check contacts, manu
controls and interlock
On load tap changer
Examine contacts, chestep by step mechanioperation, end positiolimit switches,emergency limit switcand brakes.
Dehydrating breather
Check oil level in the and ensure air passagare free.
Ventilators Check that air passagare free.
Bushings
Check the oil dielectric strength moisture content.
HALF YEARLY
Oil cooler Check for pressure te
Insulation resistanceof transformer
Compare the values wcommissioning value.
Tap changer filterwherever provided
Check the free flow ofin the filter.
Cooling fans
Check vibrations ofimpellers and shaft.
NOTES :
1) In addition to the above instructions, reference should also be made to IS : 1886 - Code of
practice for installation and maintenance of transformers.
2) The inspection schedule specified for longer periods automatically includes those specified
for shorter periods.
3) All maintenance test results and observations should be specifically recorded.
4) Where matter given in the inspection book differs from that given in IS or BS referred to,
294
-
7/27/2019 trafo erection and commissioning
29/30
the transformer user should follow the instruction book.
5) In case of anything abnormal occuring during service, advice from suppliers should be
obtained giving them complete particulars as to the nature and extent of occurence,
together with the nameplate particulars in order to assist identification of the transformer.
6) Di-electric strength of at specified in the instruction manual is breakdown values with 2.5
mm gap - as given in IS : 335/1972.
7) As-efforts are being constantly made to improve designs and service, the transformer
supplied may differ in minor details from data given herein.
8) Any additional information required by the customer will be gladly supplied.
DOS FOR POWER TRANSFORMER
1. Check and thoroughly investigate the transformer whenever any alarm or protection is
operated.
2. Check the diaphragm of the relief vent, if cracked or broken, replace it.
3. Attend the leakages on the bushing immediately.
4. Examine the bushing for dirt deposits and coats and clean them periodically.
5. Check the oil in transformer and OLTC for. di-electric strength and moisture content andtake suitable action for restoring the quality of oil as per table-A of Maintenance Schedule.
6. Check the oil level in oil Clip and ensure air passages are free in the breather. If oil is less,
make up tile all.
7. Check the oil for acidity and sludge as per table-A of Maintenance Schedule.
8. If inspection covers are opened or any gasket joint is tightened then tighten the bolts
evenly to ovoid uneven pressure.
9. Check and clean the relay and alarm contacts. Check also their operation, and accuracy
and if required change the setting.
10. Check tile protection circuits periodically.
11. Check the pointers of all gauges for their free movement.
12. Clean the oil conservator thoroughly before erecting.
13. Check the buchholz relay and adjust the floats, switches, etc.14. Inspect the painting and if necessary retouching should be done.
15. Check the OTI and WTI pockets and replenish the oil, if required.
16. Remove the air vent plug of the diverter switch before you energise the transformer.
17. Check the oil level in the diverter switch and if found less, top up with fresh oil conforming
to IS:335
18. Check the gear box oil level, if less, top up with specified oil.
19. Examine and replace the burnt or worn out contacts as per table-A of Maintenance
schedule
20. Check all bearings and operating mechanism and lubricate them as per schedule.
21. Open the equalising valve between tank and OLTC, wherever provided at the time of filling
the oil in the tank.
22. Close the equalising valve between tank and OLTC during operation.
23. Connect gas cylinder with automatic regulator transformer is to be stored for long, in order
to maintain positive pressure.
24. Fill the oil in the transformer at the earliest opportunity at site and follow storage instructions.
295
-
7/27/2019 trafo erection and commissioning
30/30
DONTS FOR POWER TRANSFORMER
1. Do not energise without thorough investigation of the transformer, wt1enever any alarm or
protection has operated.
2. Do not re-energise the transformer, unless the buchholz gas is analysed.
3. Do not re-energise the transformer without conducting all pre-commissioning checks. The
results must be comparable with results at works.
4. Do not handle the off- circuit tap switch when the transformer is energised.
5. Do not energise the transformer unless the off-circuit tap switch handle is in locked
position.
6. Do not leave off-circuit tap switch handle unlocked.
7. Do not overload the transformer.
8. Do not leave tertiary terminals unprotected outside the tank, connect them to tertiary
lightning arrestors protection scheme when connected to load.
9. Do not allow WTI OTI temperature to exceed 750C during dry out of transformer, and filter
machine temperature beyond 850C.
10. Do not parallel transformers which do not fulfill the condition given in clause 2.25
11. Do not use low capacity lifting jacks on transformer for jacking.12. Do not move the transformer with bushings mounted.
13. Do not overload the transformer other than the specified limits as per IS : 6600.
14. Do not change the settings of WTI and OTI alarm and trip frequently. The setting should
be done as per the site condition.
15. Do not leave red pointer behind the black pointer in OTI and WTI.
16. Do not meddle with the protection circuits.
17. Do not leave any connection loose.
18. Do not allow conservator oil level to fall below 1/4 level.
19. Do not allow oil lewd to fall in the bushings, they must immediately be topped up.
20. Do not leave marshalling box doors open, they must be locked.
21. Do not switch off the heater in marshalling box except in summer.
22. Do not allow dirt and deposits on bushings, they should be periodically cleaned.23. Do not allow unauthorised entry near the transformer.
24. Do not leave ladder unlocked, when the transformer is ON in service, in case it is
provided.
25. Do not change the sequence of valve opening for taking standby pump and motor into
circuit.
26. Do not switch on water pump unless oil pump is switched all.
27. Do not allow water pressure more than oil pressure in differential pressure gauge.
28. Do not mix the oil, unless it conforms fully to IS : 335.
29. Do not allow inferior oil to continue in transformer. The oil should be immediately processed
and to be used only when BDV conforms to IS : 335.
30. Do not continue with pink silicagel, it should immediately be changed or regenerated.
31. Do not leave secondary terminals of an unloaded CT open
32. Do not commission the transformer in case IR values are not satisfactory.
33. Do not continue to run the transformer with relief vent diaphragm broken or cracked.
34. Do not store transformer for long after reaching site. It must be erected and commissioned
at the earliest.
35. Do not keep the transformer gas filled at site for a longer period.
296