1. Improper configuration of high and low voltage fuses in distribution transformers. There is a widespread phenomenon that the fuses on transformers are overloaded. When the transformers are seriously overloaded, the transformers are burned down.
2. There is no fuse on both sides of high and low voltage distribution transformer. Some of them have been equipped with drop fuses and horn insurance, but their fuses are mostly replaced by aluminum or copper wires, resulting in low-voltage short circuit or overload, the fuses can not fuse normally and burn transformers.
3. Because there are many lighting lines in rural areas, most of them are supplied by single-phase power supply. In addition, the randomness of jumpers and the inadequate management in construction cause the partial operation of distribution load. Long-term use results in aging of insulation of a phase coil and burning of transformer.
(1) Privately adjusting tap changers, resulting in inadequate tap changers, poor contact and burning.
(2) The poor quality of tap changer results in incomplete contact of star contacts and short circuit or ground discharge.
5. Oil seepage is the most common abnormal appearance of transformer. Because the transformer body is full of oil, there are rubber beads and rubber pads at all connecting parts to prevent oil leakage. After a long period of operation, some rubber beads and cushions in transformers will crack and cause oil seepage. As a result, the insulation performance decreases after dampness, the discharge short circuit, and the transformer is burned down.
6. The high and low voltage lines of distribution transformers are mostly introduced by overhead lines, because arresters are not put into operation in time or installed with 10 kV arresters. The transformer is burnt down when lightning strikes occur.
7. Multi-point grounding of iron core.
8. When the low-voltage side of distribution transformer is grounded and short-circuit occurs between phases, a short-circuit current 20-30 times higher than the rated current will be generated. Such a large current acting on the high-voltage winding will cause great mechanical stress inside the coil, which will lead to the compression of the coil. After the short circuit breakdown is relieved, the stress also disappears. If the coil is repeatedly subjected to mechanical stress, its insulation beads, rubber pads, etc. will loose and fall off; the core splint bolt will also loose, and the high-voltage coil will distort or crack. In addition, high temperature will also occur, which will cause the transformer to burn down in a very short time.
9. Man-made damage: 1. Copper screw is the lead wire of transformer, and the overhead wire is usually made of aluminium cored rubber. It is easy to produce electrochemical corrosion between copper and aluminium. (2) Casing flashover discharge is also a common abnormal phenomenon in transformers.
1. High and low voltage fuses should be installed in time when new construction is under way. In the operation of transformer, the fuse should be replaced in time when it is found burnt or stolen.
2. Reasonable configuration of high-voltage and low-voltage fuses: 1. Fuses with rated current (1.5-2.0) should be installed in transformers with capacity over 100 kVA. (2) Transformers with capacity below 100 kVA shall be equipped with fuses with rated current (2.0-3.0). The low-voltage side fuses should be selected at a slightly higher rated current.
3. Strengthen the work of power load measurement, use clamp ammeter to measure the load of each distribution transformer when the peak period comes, adjust the load reasonably, and avoid three-phase unbalanced operation of the distribution transformer.
4. For the low voltage side voltage of 10kV distribution transformer in the range of + 7%-10%, it is generally not allowed to adjust tap changer. When adjusting tap-changer, it should be adjusted by repairing technicians.
5. Check periodically whether the three-phase current is balanced or exceeds the rated value. If the three load currents are seriously unbalanced, timely measures should be taken to adjust them.
6. Before the arrival of thunderstorm season every year, all lightning arresters on distribution transformers should be sent to the repair and test department for inspection, and installed in time after the test is qualified.
7. Before putting into operation, the following inspection work should be done well: 1. Switching on and off three times with load, and no misoperation shall be allowed. (2) Three times with the test button, the correct action should be taken. 3. Grounding test with test resistance for three times should be done correctly.
8. Clean up the dirt on the surface of distribution transformer bushing regularly: Check whether the bushing has flashover marks, whether the grounding is good or not, and whether the lead used for grounding is broken, welding and fracture. The grounding resistance shall not be greater than 4_measured by megaohmmeter.