1. Oil-immersed transformers have no fuses on both sides of high and low voltage. Although some have been fitted with drop-out fuses and claw fuse, most of their fuses are replaced by aluminum or copper wires, resulting in low-voltage short-circuit or overload, the fuses cannot normally fuse and burn the oil-immersed transformer.
2. The high and low voltage fuses of the oil-immersed transformer are not properly configured. The fuse on the oil-immersed transformer is generally over-configured. When it is seriously overloaded, the oil-immersed transformer will be burned.
3. Due to the large number of rural lighting lines, most of them use single-phase power supply, coupled with the randomness of jumpers during construction and the inadequate management, resulting in the partial phase operation of the distribution transformer load. Long-term use will cause the aging of the coil insulation of a certain phase and burn the oil-immersed transformer.
4. Tap switch:
(1) Adjust the tap switch privately, causing the distribution transformer tap switch to not be in place, poor contact and burnt.
(2) Poor quality of tap changer, causing incomplete contact of the star contact position, short circuit or discharge to the ground.
5. Oil leakage is a common appearance abnormality of oil-immersed transformers. Since the body of the oil-immersed transformer is filled with oil, there are rubber beads and pads at each connection part to prevent oil leakage. After a long time of operation, some rubber beads and pads in the oil-immersed transformer will age and crack and cause oil leakage. As a result, the performance of the insulation is reduced after being damp, the discharge is short-circuited, and the oil-immersed transformer is burned.
6. Most of the high and low voltage lines of oil-immersed transformers are introduced by overhead lines, because the arrester is not put into operation in time or the 10kV arrester is not installed. The oil-immersed transformer will be burnt down when lightning strikes.
7. The iron core is grounded at multiple points.
8. When the low-voltage side of the oil-immersed transformer is grounded or short-circuited between phases, a short-circuit current 20-30 times higher than the rated current will be generated. Such a large current acts on the high-voltage winding, and a large mechanical stress will be generated inside the coil. , This mechanical stress will cause the coil to compress. The stress disappears after the short-circuit fault is removed. If the coil is repeatedly subjected to mechanical stress, its insulating rubber beads, rubber pads, etc. will loosen and fall off; the iron core splint bolts will also loosen, and the high-voltage coil will be distorted or cracked. In addition, high temperature will be generated, which will cause the oil-immersed transformer to burn out in a very short time.
