Testing and Erection of Transformers

A.TRANSFORMER TESTING SUMMARY CHART

B.TRANSFORMER ERRECTION

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

Precautions

Instruction To Erection Personnel: All the people 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 securely tied with a cotton tape to a suitable point so that they can be recovered if accidentally dropped inside.

Cleaning: Fibrous materials should not be used for cleaning. The presence of loose fibers 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 and non-fluffy cloth.

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

Condensation: Transformer oil and other solid insulation that is normally used in transformer construction absorb moisture easily, particularly when cold. Condensation can be caused if the interior of a tank is exposed to the atmosphere. But, this can be minimized by taking adequate care. The transformer can be protected from “damp” hazard by circulating warm and dry oil through it until a temperature is 50 to 100 C above ambient. This should be done before allowing access to the interior of the tank. Warm oil should be circulated all the time while the 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 should be done. Retouching of paint may be required at the places where the paint is damaged during transit.

Location and Foundation:

A leveled and firm foundation that is strong enough to support the complete weight of the transformer and prevent accumulation of water should be provided. Continuous external vibrations may set up physical movements on the core and windings and in turn, may lead to a breakdown. While locating the transformer, care should be taken to provide adequate clearances from the live parts of the transformer to earth parts. Easy access should be provided all around like, 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 their wheels should be locked to prevent any accidental movement…
At the place where the transformer is enclosed in the chamber, it should be ensured that it gets goods ventilation.

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

Erection of transformer:

A sequence of erection:

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 the erection of transformer, should be referred before commissioning installation works.

Precautions

Fitting of rollers

Oil check

Conservator

Buchholz relay and pipework

Silica gel dehydrating

Explosion Vent

Terminals HV-LV bushings or cable boxes, CT terminals etc

Topping up of oil

Radiators

Temperature indicators

Marshaling boxes

Details of erection:

a.Rollers:

Before mounting of rollers, they should be checked for soundness of casting and to ensure that bearing surface is not damaged. The bearing surface should be greased or oiled before mounting.

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

b. Oil check:

c. Conservator :

d. Buchholz relay:

e. Silica gel Dehydrating breather :

Breather is connected to the conservator through pipework. Breather assembly should be suitably clamped so as to prevent vibration. Fill up transformer oil through filling a hole, in the bottom compartment of the breather, up to the filling level mark. Air entry hole is sealed with the adhesive tape, which should be removed for free passage of air.

Check that silica gel is blue in color, if not, reactivate or replace it with fresh gel.

Remove cork/ Blanking tape from a top screwed hole and fix breathe on the pipework.

f. Explosion Vent

Explosion vent is provided with a Bakelite diaphragm. Normally, the transformer is dispatched fitted with explosion vent. If dismantled for the purpose of transport, remove blanking plate from the bottom of the vent before assembling it on the tank. Check whether the vent is corroded from inside. Rust should be completely removed and the inside section should be painted with oil resistant paint.

Before assembly, make sure that the top and bottom diaphragms, if provided, are intact.

The 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 against specific requirement which connects to the top of explosion vent and then vents it to the atmosphere through the breather.