Transformer Testing

We offer highly effective Transformer Testing, which is very important for an efficient working of the transformer and its reliability. High performance and durability of Transformers can be achieved by using superior quality raw materials and technically advanced machines thus ensuring high standards of workmanship during production. Our company carries-out various tests at different stages of manufacturing process. The final tests on fully assembled transformer also assure suitability of the equipment for satisfactory performance. Our tests are conducted as per norms of IS2026/1EC726/BS171 to ensure reliable and efficient performance of the transformer during its lifetime.

After finalization of the erection work the following tests should be conducted:
- Measurement of winding resistance
- Verification of voltage ratio
- Verification of vector group
- Measurement of no load current and losses
- Measurement of impedance and load losses
- Measurement of insulation resistance
- Power frequencies withstand voltage
- Induced over voltage test
- Air presser test

Type Tests
- Impulse voltage withstand test.
- Temperature rise test.
Ratio, Polarity and Phase Relationship:
The ratio should be checked at all taps and between all the windings. It is checked by applying a single-phase 230V (approx) supply on the high voltage side and measuring the voltage on the low voltage side at all tap positions. The measured voltage on LV side shall conform to declining trend between tap (min) to tap (max) position for all phases. Polarity and interphone connections are checked while measuring the ratio. This can be checked by the avometer method. The primary and secondary windings are connected together at points indicated in sketch shown below. A low voltage three-phase supply is then applied to the HV terminals. Readings obtained should be the vectorial sum of the separate voltages of each winding under consideration.

Pre Test Inspection

- Sample of oil taken from the transformer and subjected to electric test (break down value) of 50KV (RMS) as specified in IS: 335.
- Release trapped air through air release plugs and valve fitted for the purpose on various fittings like radiators, bushing caps, tank cover, Bushing turrets etc.
- The float lever of the magnetic oil level indicator (if provided) should be moved up and down between the end positions to check that the mechanism does not stick at any point. If the indicator has signaling contact they should be checked at the same time for correct operation. Checking the gauge by draining oil is a more positive test.
- Check whether gas operated (if provided) is mounted at angle by placing a spirit level on the top of the relay. Check whether the conservator is filled upto the filling oil level marked on plain oil gauge side and corresponding to the pointer reading in MOG side. Check the operation of the alarm and trip contacts of the relay independently by injecting air through the top cocks using a dry air bottle. The air should be released after the tests. Make sure that transformer oil runs through pert cock of buchholz relay.
- Check alarm and trip contacts of WTIs, dial type thermometer, magnetic oil gauge etc. (if provided).
- Ensure that off circuit switch handle is locked at the desired tap position with padlock.
- Make sure that all valves except drain, filter and sampling valves are opened (Such as radiator valves, valves on the buchholz relay pipe line if provided).
- Check the condition of silica gel in the breather to ensure that it is active and colour is blue. Also check that the transformer oil is filled in the silica gel breather upto the level indicated.
- Check tightness of external electrical connections to bushings.
- Give a physical check on all bushing for any crack or any breakage of porcelain. Bushing with cracks or any other defects should be immediately replaced.
- Check the neutral earthing if specified. Make sure that neutrals of HV I LV are effectively earthed.
- Tank should be effectively earthed at two points.
- Check that the thermometer pockets on tank cover are filled with oil.
- If the oil temperature indicator is not working satisfactorily, loosen and remove the thermometer bulb from the pocket on the cover and place it with a standard

After Commissioning

- Check the o/p voltage in all phases before loading.
- Distribute the load equally on all phases.
- Check the oil level once in a day.
- Check the winding temp & oil temp once in a hour.
- Check the tightness of the all electrical connections, bolts & nuts once in a 6 months.
- Check the BDV of the oil once in a year.

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