Indian code of Practice for Institution and a Maintenance of Transformer IS:10028 generally covers all the relevant aspects of the special attention required at the time of erection of transformer, should be referred before commissioning installation works.


Instruction To Erection Personnel : Persons Having access to the interior of the transformer while inspection, fitting bushing or any other fittings, should empty their pockets and all loose articles. Spanners and other tools in use should be sccurely tied with a cotton tape ta a suitable point so that they can be recovered if accidentally fropped inside

Cleaning : fibrous cleaning materials should not be used. The presence of loose fibres in suspension with transformer oil can reduce its insulation property. If cleaning or wiping is necessary, this should be done with clean dry oil using soft non-fluffy cloth

Fire risk: Transformer oil is inflammable and under certain circumstances in a confined place become explosive. Naked light and flame should never be used near the transformer

Condensation: Transformer oil and other solid insulation 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 taking adequate care this can be minimized. The transformer can be protected form “damp” hazard by circulating warm and dry oil through it until temperature is 50 to 100 C above ambient. This should be done before allowing access to the interior of tank. Warm oil should be circulated all the time while transformer is open to atmosphere.

Painting : Corroded components should be cleaned thoroughly to remove the rust, dirt and grease and repaint with one coat of red oxide primer and two coats of enamel paint. Retouching of paint may be required where paint is damaged during transit.

Location and Foundation:
A leveled and firm foundation strong enough to support complete weight of transformer and prevent accumulation of water should be provided. Continuous external vibrations may set up physical movements on core and windings and in turn lead to the breakdown.

While location transformer care should be taken to provide adequate clearances from the live parts of transformer to earth parts. Easy access should be provided all round and to diagram plate, thermometer, valves, oil gauges etc. so that they can be easily reached or read.

Suitable rails or tracks should be used for rollers and wheels should be locked to prevent accidental movement…
Where transformer is enclosed in chamber it should be ensured that it gets goods ventilation.

Wherever transformers are mounted on poles the structure should be strong enough to withstand weight of the transformer, wind pressure and other atmospheric conditions

Erection of transformer:

Generally small transformers upto 1000 KVA are dispatched oil fitted with all fittings. Fittings dismantled to facilitate transport, may be reassembled in the following sequence depending on the site conditions

Sequence of erection:

Fitting of rollers

Oil check
Buchholz relay and pipe work
Silicagel dehydrating
Explosion vent
Terminals HV-LV bushings or cable boxes, CT terminals etc
Topping up of oil


Temperature indicators

Marshalling boxes

Details of erection:
All fittings and accessories should be assembled as shown in outline drewing.


Before mounting of rollers they should be checked for soundness of casting and that bearing surmace is not damaged

Bearing surface should be greased or oiled before mounting

Assembly of rollers become simple if the transformer is lifted by overhead crane or pully block. Transformer may be jacked up with mechanical or hydraulic jacks.(Jacking pads are provided for transformers 1600 KVA and above). Height of jacking pads from ground, without wheels in positions, is not less than 300 mm. Suitable wooden or steel packing may be given under jacks to raise the jack height

b. Oil check:

A sample of oil should be taken out from bottom of tank and tested for the Electric strength, (break – down voltage) which should not be below 30 KV (RMS) when tested on a standard test as specified in IEC – 600296 Table 1-9.(Electrode dia. 120.5 mm polished, electrode gap 2.5 mm # 0.1). The electric strength shall be arithmetic mean of the six results on same sample of oil

c. Conservator :
When Dismantled for transport (Ref .3.1)

Before assembly of conservator ,make sure that inside of vessel and pipe work is free from rust ,dust,grease and moisture. if found corrode ,clean the rust and repaint with oil resistant paint from inside.
Enamel paint given is on the outside on a coat of red oxide-zinc chromate primer

Mount conservator on the corresponding supports in tank cover.Pipe work should be assembled in the following scwuence. Conservator through Buchhloz relay to tank .conservator to silicagel breather

Magnetic oil gauge shouldbe assembled on position.

Plain oil gauge window glass should be checked for the cracks which may lead to oil leaks and entry of moisture in the conservator .

Gasket should be tightened uniformly to make joints leak proof deteriorated and leak gaskets should be replaced

d. Buchholz relay
Assembly precautions (if dismantled )
Relay pipe work should 3 deg .to 7 deg. upwards towards conservator.
Arrow heads on the body should be pointing towards the conservator
Floats which operate elements should be free.
Check that mercury switches are intact
Test alarm and trip mechanism

In order to test alaram an trip mechanism, the relay is provided with two separate petcocks which enable air to be injected into the body of the relay. for testing injected air using a cycle pump or any other suitable device untill switch operates (check continuity of contacts)

To test trip elements the vallve controlling the bottle is opened quickly so that air or oil rushes in, impinges on the flap and depresses it operating the switch

On each realy petcock is provided for taking out samples and releasing gas from the top of relay housing

Testing of relay may be carried out after fitting in the conservator pipe, and filling of oil in conservator .it is recommended that the relay should not be taken apart and under no circumstances should any alteration be made to operating floats or flaps

e. Silicagal Dehydrating breather :
Breather is connected to the conservator through a pipe work .breather assembly should be suitable clamped to prevent vibration

Fill up transformer oil through filling hole, in the bottom compartment of breather upto the fillling level mark .air entry hole is sealed with the adhesive tape, which should beremoved for free passage of air.

Check that sili9cagel is blue in colour , if not , reactivate or replace with fresh gel.

Remove cork/ Blanking tape from top screwed hole and fix breathe on the pipe work

f. Explosion vent

Explosion vent is provided with a bakelite diaphragm. normally transformer is dispatched fitted with explosion vent .if dismantled for the transport, remove blanking plate from bottom of vent before assembly on tank

Check whether inside of vent is corrode. rust should be completely removed and inside painted with oil resistant paint

Before asembly make sure that top and bottom diaphragms if provided are intact.

Diaphragm should be held between two gaskets and care should be taken to clamp the flanges uniformly to prevent cracking of diaphragm

Pressure equalizer pipe may be provided on against specific requirement which connects top of explosion vent and vents its to the atmosphere through the breather.

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