How to Handle Automatic Tripping of Transformers During Operation

Handling Automatic Tripping of Transformers in Operation

1. After the circuit breakers on all sides of the transformer trip automatically, turn the control switch of the tripped breaker to the post-trip position, quickly switch over to the standby transformer, adjust the operating mode and load distribution, and keep the power system and its equipment operating normally.

2. Check the signal drop flag to identify which protection relay operated and verify whether the operation is correct.

3. Confirm whether a system fault has occurred and clarify the nature of the fault.

4. The transformer may be re-energized without full inspection upon approval from the supervisor under the following conditions (only one trial reclosure is permitted):

• Accidental manual contact with protection devices triggering breaker tripping;

• Obvious false tripping of protection relays;

• Only the low-voltage overcurrent or time-limit overcurrent protection of the transformer operated, while the fault occurred on downstream equipment of the tripped transformer without its corresponding protection acting, and the fault has been isolated.

5. If main protections such as differential protection, heavy gas protection or instantaneous overcurrent protection operate with obvious impact during the fault, conduct a thorough inspection of the transformer and its connected system, cut off power supply and measure insulation resistance. The transformer must not be put into operation until the root cause is identified. It is strictly prohibited to force re-energization of the transformer regardless of whether standby power is available in the system.

Transformer fire is a hazardous accident. Transformers contain large amounts of flammable substances; delayed disposal may lead to explosions or spread of fire.

Main Causes of Transformer Fires

1. Damaged bushings and flashover: Transformer oil flows out under the pressure of the conservator and ignites on the top cover.

2. Internal transformer faults rupture the tank or radiators, causing burning transformer oil to spill over.

Emergency Procedures for Transformer Fires

1. Open all circuit breakers on every side of the transformer to cut off all power sources, and immediately switch to the standby transformer to restore power supply.

2. Shut down all cooling equipment.

3. If the main transformer or high-voltage auxiliary transformer catches fire, disconnect the generator first.

4. If oil burns on the transformer top cover, open the emergency drain valve at the bottom to release oil to a safe level. Do NOT drain oil if the fire originates inside the transformer, to avoid explosion risks.

5. Activate fire suppression equipment promptly, such as dry powder fire extinguishers or foam fire extinguishers. Notify the fire brigade if necessary.

For such accidents, transformer protection relays should trip the circuit breakers automatically. If breakers fail to open due to faults, manually trip them immediately and disconnect all isolating switches that may feed power back to the transformer.