Technology Literature

What are the parts with the highest failure rate of transformers?

The most common fault parts of transformers mainly include lead insulation faults, iron core insulation faults, tap changer faults, etc. The fault handling of transformers focuses on the handling of heavy gas protection actions, the handling of automatic tripping of transformers, and the emergency handling of transformer fires. .

First. Common fault parts of transformers

1. Main insulation and turn-to-turn insulation faults of windings

The main insulation and inter-turn insulation of the transformer winding are the parts that are prone to failure. The main reason is: due to long-term overload operation, poor heat dissipation conditions, or long service life, the transformer winding insulation is aging and brittle, and the electrical strength is greatly reduced. ;The transformer has been impacted by short circuit for many times, causing the winding to be deformed by force, which hides insulation defects. Once the voltage fluctuation is encountered, the insulation may be broken down; at the reinforcement section of the high-voltage winding or the low-voltage winding part, due to the expansion of the overall insulation, the insulation is expanded. The blockage of the oil passage will affect the heat dissipation, the winding insulation will be aged due to overheating, and a breakdown short circuit will occur; due to the imperfect lightning protection facilities, insulation breakdown will occur under the action of atmospheric overvoltage.

2. Lead insulation failure

The lead wire of the transformer is connected to the external circuit through the inner cavity of the transformer bushing. The lead wire is supported and insulated by the bushing. Because the upper end cap (general cap) of the bushing is not tightly sealed, water enters, and the main insulation of the lead wire is damaged by moisture, or the transformer is damaged. Severe shortage of oil will expose the lead wires in the fuel tank to the air, causing internal flashovers, and failures will occur at the lead wires.

3. Core insulation failure

The transformer iron core is made of stacked silicon steel sheets, and there is an insulating paint film between the silicon steel sheets. Due to the poor fastening of the silicon steel sheets, the paint film is damaged and eddy current occurs, resulting in local overheating. Similarly, the core screws that clamp the iron core If the insulation is damaged, overheating will also occur. In addition, if there are iron filings or welding slag left in the transformer, the iron core will be grounded at two or more points, which will cause iron core failure.

4. Transformer bushing flashover and explosion

The high-voltage side of the transformer (110kV and above) generally uses capacitor bushings, which have trachoma or cracks due to poor porcelain; the capacitor core is defective in manufacturing, and there is free discharge inside; the bushing is not well sealed, and there is oil leakage; the bushing Severe fouling may cause flashover and explosion. Common fault parts of transformers_Transformer automatic and fire accident handling.

5, the tap switch failure

The transformer tap changer is one of the common fault parts of the transformer.

The tap changer is divided into two types: no-load voltage regulation and on-load voltage regulation. Common causes of failures:

1), no-load tap changer

Due to the pressure contact for a long time, there will be insufficient spring pressure and uneven roller pressure, which will reduce the effective contact area of the tap changer connection part, and the silver-plated layer of the contact part of the connection part will wear off, causing the tap changer to heat up during operation. Damage; poor contact of the tap changer, poor connection and welding of the lead wires, and can not withstand the impact of the short-circuit current, causing the tap-changer to be burned out by the short-circuit current and malfunction; switch accident

2), on-load tap-changer

For transformers with on-load tap changers, the oil tank of the tap changer and the oil tank of the transformer are generally not connected to each other. If the oil tank of the tap changer is seriously lacking in oil, the tap changer will have a short-circuit fault during switching, which will cause the tap changer to fail. Burned out. For this reason, the oil level of the two fuel tanks should be monitored separately during operation; the failure of the tap changer mechanism includes: due to the jam, the tap changer stops at the process position, causing the tap changer to burn out; the tap changer The oil tank is not tightly sealed and water seeps and leaks oil. The oil is not inspected and tested for many years, which causes the oil to be dirty and the insulation strength is greatly reduced, resulting in failure. Then arcing occurs and causes a fault.

Second, the treatment of transformer automatic tripping

When the transformer in operation automatically trips, the operator should quickly take the following measures:

1. When the circuit breakers on each side of the transformer automatically trip, operate the control switch of the trip circuit breaker to the position after the trip, and quickly put the backup transformer into operation, adjust the operation mode and load distribution, and maintain the operation system and its equipment in a normal state.

2. Check what kind of protection action the dropped card belongs to and whether the action is correct.

3. Understand whether the system is faulty and the nature of the fault.

4. If it is in the following situations and with the consent of the leader, it can be tested without inspection: the circuit breaker is tripped by accidental touch protection; the protection is tripped due to obvious malfunction; the transformer only acts for low-voltage overcurrent or time-limited overcurrent protection, and at the same time trips the transformer to the next level. If the level equipment fails and its protection does not act, and the fault has been removed, but the test transmission is only allowed once.

5. If it is a main protection action such as differential, heavy gas or current quick-break, and there is an impact phenomenon in the event of a fault, it is necessary to conduct a detailed inspection of the transformer and its system, power outage and measure the insulation. Before the cause is found, it is forbidden to put the transformer into operation Operation. It must be pointed out that regardless of whether the system has a backup power supply, it is absolutely not allowed to force the transformer.

3. Transformer catches fire

When the transformer is running, due to the damage or flashover of the transformer bushing, the oil flows out under the action of the oil pressure of the oil pillow, and burns on the top cover of the transformer; the internal failure of the transformer causes the oil to burn and rupture the casing, etc. The transformer catches fire , the following actions should be taken promptly:

1. Disconnect the circuit breaker on each side of the transformer, cut off the power supply on each side, and quickly put into the standby transformer to restore the power supply.

2. Stop the cooling device from running.

3. When the main transformer and high power plant are on fire, the generator should be disconnected first.

4. If the oil burns on the top cover of the transformer, open the lower accident release throttle to drain the oil to the proper position. If the inside of the transformer catches fire, the oil cannot be drained to prevent the transformer from exploding.

5. Use fire extinguishing equipment to put out the fire quickly. For example, use dry fire extinguisher or foam fire extinguisher to put out the fire. If necessary, notify the fire brigade to put out the fire.

4. Handling of heavy gas protection actions

During the operation of the transformer, due to the internal fault of the transformer or the fault of the relay protection device and the secondary circuit, the heavy gas protection action is caused, and the circuit breaker is tripped. When the heavy gas protection action is tripped, the central accident sound will sound, and all sides of the transformer will be disconnected. The green indicator light of the transformer flashes, the light signs of "heavy gas action" and "drop card not reset" are on, the heavy gas signal light is on, and the indicator of the transformer meter is zero. At this time, the operating personnel on duty should check and deal with the transformer as follows :

1. Check whether the oil level, oil temperature and oil color have changed, check whether the explosion-proof pipe is broken and inject oil, check whether the respirator and casing are abnormal, and whether the transformer shell is deformed.

2. Immediately take gas and oil samples for chromatographic analysis.

3. According to the phenomenon when the transformer trips (such as whether there is an impact in the system, whether the voltage fluctuates), external inspection and chromatographic analysis results, determine the nature of the fault and find out the cause. Do not close the switch until the cause of the heavy gas protection action is found. Power transmission.

4. If no abnormality is found after inspection, but it is indeed caused by a secondary circuit fault, the differential and overcurrent protection can be switched on, and the heavy gas protection can be switched on or off, test power on once, and strengthen monitoring.