Sunday, November 16, 2014


Since transformer is important asset & electrical equipment on which efficiency of plant as well as economy of industry is depends, so proper handling and maintenance is must, here we are giving some important tips through which we can taken care the transformers perfectly:

1) Visual Inspection On Receipt of Transformer & Storage:

The transformers are dispatched as per the requirement. Before unloading the transformer from the carriage, examine if there is any missing parts or damage like leaks, cracks, loose nuts etc. and if there is, inform the manufacturer before starting repair. The transformer is designed and manufactured to have sufficient strength to stand any vibration in transit, and so if no abnormality is found after checking every part, it can be installed, commissioned & operated.

All accessories should be stored in a covered dry place.  All pipe work, conservator, radiators should be stored with their blanking plates which prevents entry of water & foreign particles. Heaters in the marshalling box should be kept energized to avoid condensation. If the erection and commissioning is undertaken beyond one year or so, repainting is recommended to avoid rusting.  

2) Preparing To Erect the Transformer

The transformer should be erected on a level foundation or surface, which should be designed by a structural or civil engineer. It should be able to bear the weight of the transformer and prevent accumulation of water. 

A foundation design incorporating a special oil soak pit or oil draining facility during fire and emergencies is strongly recommended for large rating transformers.

The transformer should be installed with easy access provided all round.  All instruments and valves should be easily read and operated.  Sufficient clearances from various live points of the transformer to earthed parts should also be maintained as per electricity rules.

For transformers installed indoors, the room must be well ventilated, so that hot air can escape easily and is replaced by cold air.

3) Precautions
a) Transformer oil is inflammable.  Under certain circumstances and in a confirmed space, the oil may become explosive.  Hence, naked lights and flames should never be brought near the transformer.

b) As far as possible, no work should be carried out during the monsoon to avoid moisture absorption by the transformer. Extreme care should be taken to prevent any foreign material from being dropped into the transformer. Spanners and other tools used should be tied with strings to the hand of the workmen, so that they can be recovered if dropped accidentally.

c) Fibrous cleaning material should not be used, since the presence of loose fibres suspended in oil can reduce its insulating properties. If any cleaning or wiping is necessary, it should be done with clean dry cloth for wiping, before fitting on transformer.

d) The transformer oil and cellulose-based solid insulation normally used in transformer construction absorb moisture easily, particularly when cold.  If access is needed to the interior of the tank during erection the transformer is best protected from moisture hazards by circulating dry and hot transformer oil until temperature is slightly above the ambient, prior to allowing access to the interior.

e) The transformer shall be erected on a level foundation.

f) For large transformers, assemble the complete transformer as per OGA drawing and fill filtered oil to required level.

g) While assembling, if water was spread in radiators and pipes, flush them with transformer oil.  Ensure that the radiator valve on tank shall be in “SHUT” position.  Remove the dummies provided at radiator header pipe and radiator valve on tank. Fix the radiators as per OGA. After fixing all the radiators, remove the radiator shut-off valve cover and rotate the valve with a special spanner which will be supplied along with the transformer.  Ensure sufficient oil is available inside the transformer tank before opening the radiator valves.  Open the air releasing plug on the radiators until little amount of oil was came out from the radiators so that trapped air will come out and close the air releasing plug tightly. Fill the filtered oil through the drain valve (keep the air releasing plug in the conservator open). 

3) Site Testing

a) Testing Equipment Required

The tools and equipment required at the site for erection and commissioning of transformers are as follows:

No. Equipment / Supplies Remarks / Purpose
1 Oil BDV testing To check BDV of oil upto 60 kV across 2.5mm gap 
2 Filtering Machine Required only for transformer assembled at site 
3 Carbon Tetra chloride For cleaning bushings
4. Insulation Resistance  Tester For Checking the Meggar Value of Transformer windings.

a) Tests To be Conduct at Site

If the foregoing instruction has been carefully followed, the transformer can now be safely put into service after pre-commissioning tests.

i) Insulation resistance 
IR values between windings and between windings to earth are to be checked; while checking these values no external lines, lightning arrestors etc., should be in circuit.  Bushings are thoroughly cleaned before taking IR values.  Generally 2500/1000/500 volts meggar motor operated is preferred Care should be taken that the lead wires of the meggar do not have joints.

ii) General Checks
a) All oil valves are in correct positions, closed or opened as required
b) All air pockets are cleared / air releasing
c) Thermometer pockets are filled with oil
d) Oil is at correct level in the transformers  
e) Earthing connections are done
f) Arcing horn gaps on bushings are properly adjusted
g) For breathing type transformers, check the condition of silica gel.  Fill oil in the oil cup of the breather.  

If all the above tests / checks are found satisfactory, allow a settling time of at least 24 hours for oil and release air from all points wherever applicable.  Now the transformer can be energized after ensuring all connections are made strictly as per the requirement. Wherever possible, the voltage should be built up in steps.  Any abnormality during commissioning such as vibration of parts, hum etc., should be observed.  After a few hours of energization at no load, the load can be applied. If any abnormalities noticed, transformer shall be switched off, should be corrected. Transformer should not be re-energized suddenly and loaded gradually.

After commissioning, the following details should be furnished to the manufacturer:

i) Details of transformer including its serial number
ii) Date of commissioning, with test results
iii) Substation / generating station where commissioned
iv) Protection given to the transformer such as lightning arrestor, differential protection, circuit breaker on HV / LV etc.
v) Loading details.

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