Talking about the Causes of Transforming the Transformer of 10 kV Distribution Network
At present, the company's 10kV distribution network transformers have suffered continuous burning accidents, causing great economic losses to the company, and also affecting power supply reliability and quality services. The author summarizes the following reasons based on the on-site investigation and analysis of the burning of the station.
1. The single-phase grounding and phase-to-phase short circuit of the low-voltage line cause the transformer to burn out. When the transformer is single-phase grounded or phase-to-phase short-circuited, it generates a fault current 20-30 times higher than the rated current. This current will cause a mechanical stress on the high-voltage winding of the transformer and destroy the insulation of the high-voltage winding. The transformer will be burned and the 10kV line will be single. Grounded or overcurrent tripped.
With the arrival of spring, there is plenty of rain and trees grow faster. Most of the low-voltage overhead lines use bare aluminum stranded wires, which are prone to single-phase grounding and phase-to-phase short-circuit when the branches touch the line. The maintenance personnel of the Taiwan area should clear the low-voltage line tree barrier to ensure the channel is good.
The phenomenon of cracking in the middle of some lanes and lanes is common, which provides the thief with the convenience of stealing electricity. Frequent stealing of electricity not only causes the loss of electricity, but also easily causes short circuit of the low-voltage line. For the maintenance of the lane line, users should be prohibited from receiving electricity when they use electricity temporarily. When temporary power is required, the power should be connected at the inlet of the metering box. Due to the defects of the metering box itself during the agricultural reform, the bird's nest phenomenon in the box is very common, which is easy to cause the fire and the zero line to be connected to the iron box shell to cause low-voltage single-phase grounding or phase-to-phase short circuit. The meter reader should remove all debris including the bird's nest in the box when reading the meter.
The low-voltage distribution device (JP cabinet) of the corresponding specification should be installed in the station area to protect the low-voltage side of the transformer. In the area where the low-voltage power distribution device has been installed, the maintenance personnel should test the total load switch once every month to check the checklist to prevent the switch from jamming and lose the protection function.
Second, the three-phase load imbalance causes the transformer to burn out. This reason is that the maintenance personnel in the Taiwan area are relatively easy to ignore and are very common. Due to the large number of rural lighting lines, most of them use single-phase power supply, coupled with the randomness of the jumper during construction and the lack of management, resulting in partial phase operation of the distribution load. For long-term use, the eddy current generated in the iron core causes the insulation of a certain phase coil to age and burn the transformer.
The unbalanced load current at the outlet of the distribution transformer should be less than 10%, the neutral current should not exceed 25% of the rated current of the low-voltage side, and the current imbalance of the low-end main line and the main branch should be less than 20%. Nowadays, the number of rural household appliances is increasing, and the load is changing at any time. This requires the maintenance personnel in the station to frequently detect the output load current of the transformer and adjust the unbalanced load in time. Three-phase load imbalance is also an important reason for increasing the line loss of the station.
Third, the lightning strike caused the transformer to burn. Spring and summer are the seasons of thunderstorms. The power facilities are distributed in the vast hilly area. There are grounding bodies everywhere. According to the lightning flashover characteristics, it is easy to become the discharge of lightning. Therefore, the transformers in the station area are often damaged by lightning waves. At this time, it is required to install a lightning arrester in the station. The lightning arrester can play the role of lightning protection. There should be two conditions: the lightning arrester test can pass the test reliably; the grounding body grounding resistance is qualified. At present, the company's arrester has basically not been pre-tested after it has been put into operation. Most of the grounding body's resistance is not qualified, which poses a safety hazard to both the human body and the equipment.
Fourth, the transformer high-voltage side fuse configuration failed to cause the transformer burned. A common defect in the area where the transformer is burned is that the high-voltage protection fuse is too large, or partially replaced by aluminum wire or low-voltage fuse. The protection fuse configuration is too large, causing the fault current to increase at the low voltage to generate a short-circuit current and prolonging the time during which the fault current continues to act on the transformer winding, and the inside of the transformer is severely damaged. Most maintenance personnel in the station area think that when there is no high-voltage fuse of the corresponding specification, it can be temporarily replaced with a low-voltage fuse of the corresponding current level. In fact, this is not correct. Transformer high-voltage protection fuses are heat-sensitive, using alloy materials, which require a certain amount of thermal energy to be blown. The low voltage fuse is current type and must be blown to the rated fuse current.
5. Insufficient transformer oil causes the transformer to burn out. When the transformer is operated for a long time, its sealing rubber beads and gaskets are aging, so that the body is oily, the oil level is lowered, the transformer winding is exposed to the air, and the insulation is lowered to cause winding turns or interphase short circuits. The maintenance personnel in the station should fill the transformer with low oil level in time. At the same time, a small amount of oil should be drained for the bottom of the transformer, and the oil with high moisture content should be released to ensure good insulation of the winding.
In short, the operation of the transformer is closely related to the maintenance personnel. As long as the operation and maintenance personnel of the distribution change are diligent, diligent, diligent, and diligent, it will surely avoid the occurrence of the distribution failure and ensure the reliability of the power supply.
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