Before putting the transformer in service, several pre-commissioning tests are required, various other instruments are also checked which are in association with the transformer. This is done by the transformer manufacturing company in India, Rajasthan Powergen.
Basic Pre- Commissioning Tests of Transformer
The value of insulation resistance must be checked. The transformer must not be connected with the lightening arrestor or any other kind of external line, during the measurement of insulation resistance. The value of IR should contain few similarities with those indicated in the transformer manufacture’s test reports. Radiator tank, oil sample from the top and the bottom of the oil tank must be checked, along with few other components such as diverter switch tank of the tap changer and the selector switch. The dielectric strength of the transformer must be greater than 50 KV. HV and LV ratio test should be performed at all tap position, similarly, all resistance measurement must be done at all tap positions and in three winding transformers, the ratio between another pair of winding is also required.
Phase relationship test is a must, whereas the tap changer should undergo following tests:
• Parallel Operation
• Local electrical operation
• Remote electrical operation
• Manual operation
• IR value of the control wiring should be checked by 500V Megger.
• The operation should be tested from one end of the range to the other, in order to inspect limit switch operation.
Low Oil Level Alarm Test:
Low oil level alarm test of the magnetic oil gauge should be examined properly.
Buchholz Relay Test:
The tripping phenomena should be tested by moving air into the test pocket provided in the relay along with the examining of Buchholz Relay operation for the alarm.
Cooling Gear Test:
• Water flow indicator and Alarm trip contact settings of differential gauge oil.
• The IR values and various setting operation of oil pumps and fans motors are supposed to be checked.
Temperature Indicator Test:
Contacts of the oil temperature indicators and winding temperature indicator for alarm contact trip should be checked and set at the required temperature.
Protecting Relay Test:
The actual operation of the differential relay, over current relay, earth fault relay and other protective relays are applicable and provides associated tripping of circuit breakers.
Marshalling Box:
Marshalling Kiosk must be checked in order to check all the wirings of various accessories or equipment.
Magnetizing Current Tests:
Measurement of magnetizing current is done by feeding 400V, three phase 50Hz supply from HV side while keeping the LV side open circuited and the value must be compared in different phases.
Various other additional checks required during the power transformer.
1. Testing clearance of air pockets.
2. Oil must be filled in the thermometer pockets.
3. Correct positioning of all oil valves in the open or closed position.
4. Checking of oil level in conservator tank, diverter switch tank and in the bushing.
5. Correct placement of Arch horns is required.
6. The polarity of CT should be checked when bushing mounted CTs.
Before commissioning of the transformer, at least 24 hours is required in order to let oil and air released from all points at six hourly intervals, to settle down into the tank. During commissioning of the transformer, the voltage should be build up slowly to the full level in about 4 to 6 hours. If tripping occurs in differential or Buchholz relay they must be investigated before re- energizing the transformer. Magnetic inrush current also affects tripping. After commissioning, measurement of current transformer circuit must be measured by the connecting clips on the meter in current transformer. Buy premium quality transformers from the leading transformer manufacturing company in India where transformers are offered after they proper conducting all the proper tests.
