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Operation and Maintenance of Voltage Transformer

1. The normal operation of the voltage transformer

(1) The voltage transformer is allowed to run for a long time under the rated capacity, but it can run beyond the maximum capacity under any circumstances.

(2) The load of the secondary coil of the voltage transformer is a high-level instrument. The secondary current is very small, which is close to the magnetizing current. The leakage inductance and voltage drop of the primary and secondary coils are also very small. Therefore, the voltage transformer is in normal operation. Close to no load.

(3) The secondary side of the voltage transformer cannot be short-circuited during operation.

(4) For voltage transformers of 60 kV and below, fuse should be installed on the primary side to prevent the accident from expanding when the transformer fails. For voltage transformers of 110kV and above, generally no fuse is installed on the primary side, because the possibility of accidents in this type of voltage transformer is very small; at the same time, the breaking capacity of the fuse is difficult to meet the requirements in the power grid of this voltage level.

(5) The operating voltage of the voltage transformer should not exceed 110% of the rated voltage.

(6) In order to ensure safety, an outlet end of the secondary winding of the voltage transformer or the neutral point of the transformer should be directly grounded to prevent the danger of high voltage from escaping to the secondary side after the insulation breakdown of the high voltage side to humans and equipment. When it is necessary to work on the base of the voltage transformer body, the transformer must be turned to the primary side, and there must be obvious displacement points on the secondary side of the voltage transformer, and the power may be cut off from other voltage transformers. The secondary circuit of the voltage transformer is reversely charged, thereby inducing a high voltage on the primary side.

(7) When starting the voltage transformer, check whether the insulation is good, whether the phasing is correct, whether the oil level is normal, and whether the connectors are correct. When resetting the voltage transformer, you should first exit the relevant protection and automatic devices, alternate the secondary side automatic air switch, or remove the secondary side fuse, and then open the primary side isolation switch to prevent backlash. And record the time when the relevant circuit stops energy metering.

2. the operation of the voltage transformer

(1) After the preparation work is over, the duty personnel can carry out the power transmission operation, put on the high and low voltage side fuses, close the outlet isolation switch to make the voltage transformer run, and then the relay protection of the voltage transformer And automatic devices.

(2) Parallel operation of voltage transformers is in a double busbar system, and each group of busbars is connected to a voltage transformer. If two voltage transformers are operated in parallel on the low-voltage side due to load requirements, at this time, check whether the bus tie breaker is closed. If not, then

After closing, parallel the low-pressure side. Otherwise, due to the unbalanced voltage on the high-voltage side, the circulation of cracks in the low-voltage side circuit will easily cause the low-voltage fuse to blow, causing the protection device to lose power.

(3) Reset of voltage transformer. In the double busbar system (in other wiring methods, the voltage transformer is reset together with the busbar), such as a voltage transformer outlet isolating switch, the voltage transformer body or the voltage transformer low-voltage side resistance needs to be repaired, the voltage must be reset The operating procedure of the transformer is as follows:

① Cancel the protection and automatic devices of the voltage transformer first. If the automatic switching device or manual switching device can be used, the protection and automatic device may not be interrupted.

②Remove the low-voltage fuse to prevent reverse charging and make the high-voltage side live.

③Open the isolation switch of the voltage transformer outlet and remove the high-voltage side fuse.

④ Carry out electrical test, use a suitable and qualified electroscope to test each phase of the incoming line of the voltage transformer. After verifying that there is no electricity, install the grounding wire, hang the sign, and after the work permit is handled, it can be replaced for maintenance work.

3. Precautions when replacing the voltage transformer and secondary coil in operation:

1) When individual voltage transformers are damaged during operation and need to be replaced, they should be replaced with voltage transformers whose voltage level is consistent with the grid voltage, the same transformation ratio, the correct polarity, and the similar excitation characteristics, and they have passed the test.

2) When replacing a group of voltage transformers, check the wiring group of the voltage transformers running in parallel and check the phase difference.

3) After the secondary coil of the voltage transformer is replaced, it must be checked to avoid wrong wiring and prevent short circuit of the secondary circuit

4) The polarity of the voltage transformer and secondary coil must be measured after replacement.

4. patrol inspection of voltage transformer operation

(1) Check that the insulator should be clean, free from damage and cracks.

(2) Check that the oil level should be normal, and the oil color should be transparent and not black, with no leakage or oil leakage.

(3) Check that the color of the hygroscopic agent in the respirator should be normal without deliquescence, and the hygroscopic agent should be replaced if the color changes more than 1/2.

(4) Check that the internal sound should be normal, without discharge and high-temperature electromagnetic vibration, and without burning odor.

(5) The inspection device should be in good condition, and the screws in each part should be firm and not loose.

(6) Check that the connection of the lead connector on the primary side should be good, without looseness or overheating; the current-limiting resistance of the high-voltage fuse and the capacitor for disconnection protection should be intact; the cables and wires of the secondary circuit should be free of corrosion and damage, and the secondary wiring should not be damaged. Short circuit phenomenon.

(7) Check that the neutral grounding of the primary side of the voltage transformer and the grounding of the secondary winding should be good.

(8) Check that the terminal box should be clean and not damp.

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