Analysis of oil-immersed transformer operation and maintenance and troubleshooting-ZHEJIANG ILANDER ELECTRIC CO.,LTD.

Analysis of oil-immersed transformer operation and maintenance and troubleshooting
Author:ilander 2021-05-11

The normal operation of the transformer depends not only on the design and manufacturing process of the transformer, but also on the day-to-day operations, maintenance and management. The occurrence of a transformer failure will greatly affect the normal operation of the power plant. Oil-immersed transformer failures affect the grid system. The operation is extremely hazardous. In order to avoid accidents, it is necessary to strengthen daily operation inspection management and formulate effective maintenance measures to ensure the safe and stable operation of the transformer. Strengthening the regular maintenance of transformers and adopting effective measures to prevent the occurrence of transformer failures are of great significance in ensuring the safe and stable operation of transformers.

1、Analysis and Treatment of Common Faults in Transformer Operation

  (1) Transformer fire is also a dangerous accident. Due to the damage or flashover of the transformer bushing, the oil flows out under the effect of the oil pressure of the oil pillow, and is burned on the top cover of the transformer; the internal fault of the transformer causes the oil to burn and the shell to break. Because transformers have many flammable substances, failure to deal with them in time may cause an explosion or a fire. In the event of such an accident, transformer protection should act to break the circuit breaker. If the circuit breaker is not disconnected for any reason, the circuit breaker shall be disconnected manually immediately, and the disconnector that may lead to the transformer power supply shall be opened, and the standby transformer shall be quickly replaced to restore the power supply, stop the operation of the cooling equipment, and extinguish the fire. When the transformer is extinguishing, it is best to use a foam fire extinguisher or a dry powder fire extinguisher. If necessary, use sand to extinguish the fire.

  (2) Tap switch failure. Transformer tap-changer is one of the common faults in transformers. Due to the pressure contact of the switch for a long time, the spring pressure will be insufficient, the effective contact area of the switch connecting part will be reduced, and the silver coating of the contact part will wear away, causing the tap changer to be damaged during operation. The bad contact of the tap changer can not withstand the impact of the short-circuit current and cause the tap-changer to burn out. In the transformer with on-load voltage regulation, the fuel tank of the tap-changer and the transformer tank are generally unrelated to each other. If the fuel tank of the tap changer is severely short of oil, a short circuit fault will occur during the changeover of the tap changer, causing the tap changer to burn out.

  (3) Transformer automatic tripping. After 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 in to adjust the operation mode and load distribution to maintain the operating system and equipment in a normal state. Check the protective action and perform an external inspection. If the check is not an internal fault but due to an external fault or human error, etc., the power supply can be input without internal inspection. In the case of primary protection actions such as differential, heavy gas, and quick disconnect, all inspections should be performed on the equipment within the scope of protection. It is forbidden to put the transformer into operation until the cause has been ascertained.

  (4) Winding main insulation and inter-turn insulation faults. The main insulation and inter-turn insulation of the oil-immersed transformer winding are parts that are prone to failure. The main reasons are as follows: Due to long-term overload operation, poor heat dissipation conditions, or long service life, the insulation of the windings of transformers is brittle and brittle, and the electrical strength is greatly reduced; the transformer is subjected to short-circuit shocks for many times to deform the windings and hide the insulation. Defects, in the event of voltage fluctuations, it is possible to breakdown the insulation; the water in the transformer oil will greatly reduce the insulation strength and cannot withstand the allowable voltage, resulting in insulation breakdown; at the high voltage winding reinforcement section or low voltage winding part, due to insulation The expansion causes the oil passage to be blocked, which affects the heat dissipation, causes the insulation of the winding to deteriorate due to overheating, and causes a breakdown short circuit; due to imperfect lightning protection facilities, insulation breakdown occurs under the action of atmospheric overvoltage.

  (5) Iron core insulation fault. The transformer core is made of stacked silicon steel sheets with an insulating film between the silicon steel sheets. Due to the poor fastening of the silicon steel sheet, turbulence is caused by the destruction of the paint film and local overheating occurs. In the same way, if the insulation core is broken, insulation may also cause overheating. In addition, if there are iron chips or welding slag in the transformer, making the iron core ground at two or more points will cause the iron core to malfunction.

  (6) Gas protection failure. Gas protection is the main protection of the transformer, light gas acts on the signal, and heavy gas acts on the trip. The following analyzes the causes of gas protection actions and how to deal with them: First, signals are sent after light gas protection actions. The reasons for this are: There are minor faults inside the transformer; there is air inside the transformer; secondary circuit faults, etc. The operating personnel should immediately check, and if no abnormalities are found, gas sampling analysis should be performed. Secondly, when the gas protection action trips, there may be a serious internal fault in the transformer, causing the oil to decompose a large amount of gas, and may also cause secondary circuit failures. When a gas protection trip occurs, you should make an emergency change before performing an external inspection. Check the explosion-proof door of the oil pillow, whether each welding seam is cracked, whether the transformer shell is deformed, and finally check the flammability of the gas.

  (7) Transformer casing failure. Mainly flashover and explosion of the casing, the high-voltage side of the transformer generally uses a capacitor bushing, due to bad casing porcelain or trachoma and cracks, lax sealing of the casing, oil leakage phenomenon; too much casing fouling, etc. May cause flashovers and explosions.