(1) Main insulation and turn-to-turn insulation failure of the winding. The main insulation and turn-to-turn insulation of the transformer windings are prone to failure. The main reasons are: due to long-term overload operation, poor heat dissipation conditions, or long service life, the transformer winding insulation is aging and brittle, and the electric strength is greatly reduced; the transformer is subjected to short-circuit shock multiple times, causing the winding to be deformed by force, hiding the insulation. Defects, in the event of voltage fluctuations, it is possible to break down the insulation; the water in the transformer oil reduces the insulation strength and cannot withstand the allowable voltage, causing insulation breakdown; at the high-voltage winding reinforcement section or the low-voltage winding section, due to insulation Expansion, the oil passage is blocked, affecting the heat dissipation, causing the winding insulation to age due to overheating, causing a breakdown short circuit; due to imperfect lightning protection facilities, insulation breakdown occurs under atmospheric overvoltage.
(2) Transformer bushing failure. Mainly due to casing flashover and explosion. Capacitor bushing is generally used on the high voltage side of the transformer. Due to poor porcelain or trapped sand and cracks, the casing is not tightly sealed and there is oil leakage. May cause flashovers and explosions.
(3) Iron core insulation failure. The transformer core is made up of silicon steel sheets, and there is an insulating paint film between the silicon steel sheets. Due to the poor fastening of the silicon steel sheet, the paint film is broken and eddy current is generated, and local overheating occurs. In the same way, the components such as the thread-piercing screw and the ferritic iron that clamp the iron core may overheat if the insulation is damaged. In addition, if there are iron filings or welding slag in the transformer, and the iron core is grounded at two or more points, the core will be faulty.
(4) The tap changer is faulty. The transformer tap changer is one of the common faults of the transformer. Since the switch is in contact with the pressure for a long time, the spring pressure is insufficient, the effective contact area of the switch connecting portion is reduced, and the silver plating layer of the contact portion is worn off, causing the tap changer to generate heat damage during operation. If the tap changer is in poor contact and cannot withstand the impact of the short-circuit current, the tap-changer will burn out and fail. In the transformer with load regulation, the fuel tank of the tap-changer and the transformer tank are generally not connected to each other. If the tap-changer oil tank is seriously deficient, the tap-changer will have a short-circuit fault during the switching, causing the tap-changer to burn out.
(5) Gas protection failure. Gas protection is the primary protection of the transformer, with light gas acting on the signal and heavy gas acting on the trip. The following is the reason for the gas protection action and the treatment: First, the signal is sent after the light gas protection action. The reason is: there is a slight fault inside the transformer; there is air inside the transformer; the secondary circuit is faulty. The operating personnel should check immediately. If no abnormalities are found, gas sampling analysis should be performed. Second, when the gas protection action trips, there may be a serious fault inside the transformer, causing the oil to decompose a large amount of gas, or the secondary circuit may be faulty. In the event of a gas protection trip, a standby change should be made first, followed by an external check. Check the oil vent explosion-proof door, whether the weld joints are cracked, whether the transformer casing is deformed or not; finally check the flammability of the gas.
(6) Processing of automatic tripping of low frequency transformers. When the circuit breakers on each side of the transformer are automatically tripped, the control switch of the trip circuit breaker is first operated to the position after the trip, and the standby transformer is quickly put into operation to adjust the operation mode and load distribution to maintain the operating system and equipment in a normal state. Check the protection action and perform an external inspection. If the inspection is not an internal fault but is caused by an external fault (traversal fault) or a malfunction of the person, the power can be supplied without internal inspection. In the case of differential protection, heavy gas, quick break and other main protection actions, all equipment in this protection range shall be inspected. It is forbidden to put the transformer into operation before the cause is found.
(7) Low-frequency transformer ignition is also a dangerous accident. Due to the damage or flashover of the transformer bushing, the oil flows out under the oil pressure of the oil pillow and burns on the top cover of the transformer; the internal fault of the transformer causes the oil to burn and the outer casing to rupture. Because the transformer has many combustible materials, failure to deal with it may cause an explosion or enlarge the fire. In the event of such an accident, the transformer protection should act to disconnect the circuit breaker. If the circuit breaker is not disconnected for any reason, the breaker should be disconnected immediately, the isolation switch that may lead to the transformer power supply is opened, and the standby switch is quickly turned on, the power supply is restored, the operation of the cooling device is stopped, and the fire is extinguished. When the transformer is extinguished, it is best to use a foam fire extinguisher or a dry powder fire extinguisher. If necessary, use sand to extinguish the fire.
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