Specific Test Before And After Commissioning of Transformer
Q. List the specific test before and after commissioning of transformer.
1. Mechanical tests
2. Electrical tests
THESE RULES MUST BE FOLLOWED FOR ALL TEST PROCEDURES.
Following is an approximate sequence for transformer testing:
1. Inspect transformer and parts for shipping damage and moisture.
2. Check nameplate and prints for proper voltages and external phasing connection to the line or bus.
3. Check calibration of all thermal gauges and hot-spot heater, bridge RTDs and associated alarm contacts. Contact settings should be similar to the following:
- One stage runs all the time (forced cooling)
- 2nd stage at 80°C
- 3rd stage at 90°C
- Hot-spot alarm 100°C (trip at 110°C when applicable)
- Top-oil alarm 80°C at 55°C rise and 75°C at 65°C rise
- OA = no fans or pumps
- FA =fans running
- FOA = fans and pumps running
4. Check and Megger all wiring point to point: Fans, pumps, alarms, heaters, tap changers, and all other devices on the transformer and interconnecting cables
5. All banks above 150 MVA should be vacuum dried. Do not apply test voltages to the winding during the vacuum drying process. Make certain the terminals are shorted and grounded during oil circulation because of the large amount of static charge that can build up on the winding.
6. After the tank has been filled with oil, confirm that an oil sample was sent to the Chemical Lab and that its results are entered in the bank test reports. Note the oil level and temperature at completion of filling.
7. Power operate to verify proper rotation of pumps and fans and correct operation of the under load (UL) tap changer, when provided. Also, check heater, alarms and all other devices for proper operation.
8. Following are the winding tests to be performed:
- Ratio and Polarity (Voltage Method or TTR). The preference is that all large power Transformers (>1 MVA) be tested with TTR test set.
- Impedance
- DC winding resistance
- Megger and Power Factor windings, bushing and arrestors. Note: Wait until 24 hours after completion of oil filling for Power Factor testing.
9. Load CT circuits overall and flash for polarity.
10. Before energization, trip-check bank protection schemes and make sure the gascollection relay is free of gas.
11. When energizing a bank or picking up load, monitor bank currents and voltages, including UL tap-changer operation.
12. Check proper phasing and voltage of the bank to the system before load is picked up. When possible, large transformers (>1 MVA) should remain energized for eight hours before carrying load.
13. Make in-service checks on meters and relays.
14. Release to Operations and report energization information to the TNE office.
15. Turn in revised prints and test reports, which should include the following:
- All test data
- Moisture and oil data
- Problems incurred
- In-service data
- Time energized and release to operation
- Any unusual problem that information will aid in future equipment testing