Causes and Treatment of Common Faults of Distribution Transformers

1. Abnormal sound: When the transformer is in normal operation, due to the alternating current passing through the magnetic flux of the transformer winding, the transformer core vibrates and produces a clear and regular “humming” sound. However, when the transformer load changes or the transformer itself is abnormal or faulty, abnormal sounds will be generated:

①The sound is heavier than usual, but there is no noise: it is generally caused by the overload of the transformer. When the transformer is overloaded, try to reduce some secondary loads to reduce the burden on the transformer or increase the capacity of the transformer;

② Sharp sound: generally caused by high transformer voltage. Too high voltage is not conducive to the operation of the transformer, and will increase the iron loss of the transformer. Therefore, timely measures should be taken to deal with it;

③ Noisy and chaotic sound: The internal structure of the transformer may be loose, and the looseness of the main parts will affect the normal operation of the transformer. Pay attention to timely maintenance;

④ There is a crackling sound of “splitting”: the insulation of the transformer winding or iron core has breakdown. This situation will cause serious accidents, so immediately power off for maintenance;

2. The oil temperature of the transformer is too high: It is not allowed for the oil temperature of the upper layer of the transformer to exceed the allowable temperature. This situation may be caused by the transformer overload, poor heat dissipation or internal failure. If the oil temperature is too high, the insulation of the transformer will be damaged, and in severe cases, the entire transformer may be burned.
3. Significant drop in oil level: Normally, the rise or fall of the oil level is caused by temperature changes, and the change will not be too large. When the oil level drops significantly, and even the oil level cannot be seen from the oil level gauge, it is because the transformer has oil leakage and oil leakage, often because the transformer oil tank is damaged, not tightened, the transformer box cover is not tightly closed or the oil level gauge caused by damage etc. If the oil level is too low, the aging of the transformer oil will be accelerated, and the insulation of the transformer will deteriorate, which will cause serious consequences. Therefore, attention should be paid to add oil in time. If the oil seepage or leakage is serious, the transformer should be stopped for repair.
4. Abnormal oil color, burnt smell: The new transformer oil is slightly transparent light yellow, and the oil color will turn light red after running for a period of time. If the oil color becomes dark, it means that the insulation of the transformer is aging; if the oil color changes Black (the oil contains carbon) or even a burnt smell, indicating that there is a fault inside the transformer (partial burning of the iron core, short circuit between phases of the winding, etc.), which will lead to serious consequences. The transformer should be stopped for maintenance and repaired. Oil treatment or replacement with qualified oil,
5. Bushing discharge to the ground: when the surface of the bushing is not clean or cracked or damaged, it will cause leakage current on the surface of the bushing, making a “squeak” flashover sound, and “beep” in rainy and foggy days The sound of discharge can easily cause discharge to the ground, which will break down the bushing and cause one phase of the transformer lead wire to be grounded. Therefore, if the bushing is found to discharge to the ground, the transformer should be stopped and the bushing should be replaced. If there is conductive debris between the bushings, it may cause discharge between the bushings, and it should be cleaned up in time.
6. High-voltage and low-voltage fuse blown: Fuse blown always indicates that abnormal operation has occurred. It should be analyzed and judged. After checking the cause and dealing with it, replace it with a suitable fuse.

①There may be three reasons for low-voltage fuse blowing: short circuit of low-voltage line, excessive load on the low-voltage side, or small selection of fuse specifications;

②The reasons for the blown high-voltage fuse are as follows: the lightning arrester is installed inside the high-voltage fuse, and the fuse blows when struck by lightning; a short-circuit fault occurs inside the transformer; The fuse itself is undersized.

7. Transformer fire: The main reasons for the fire of the transformer during operation are: the insulation damage of the iron core bolts; the insulation damage between the iron core silicon steel sheets, the short circuit between the high-voltage or low-voltage winding layers; and overload etc.

When the transformer is on fire, the source should be cut off first, and then use non-conductive fire extinguishers (such as dry powder fire extinguishers, etc.) and dry sand to extinguish the fire. It is strictly forbidden to use water or other conductive fire extinguishers to extinguish the fire, especially when the fire is live.