Analysis of Causes and Precautionary Measures for Burnout of Distribution Transformers

In recent years, the distribution transformers in rural areas of our power supply station have been damaged from time to time, especially during the periods of peak usage, thunderstorms, and high temperatures. After long-term follow-up investigations and on-site testing, the author analyzed and summarized the main reasons and preventive measures that led to the destruction of distribution transformers.

1. Causes of burning (1) The distribution transformer protection configuration is not suitable. Some distribution transformers have no fuses on the high and low voltage sides. Some of them are equipped with drop-type fuses. However, aluminum or copper wire is used instead of fuses. When low-voltage short-circuit or overload occurs, distribution transformers and distribution transformers cannot be normally burnt. The high and low pressure melt disposition capacity is too large, causing the distribution transformer to be heavily overloaded and burned.

(2) The total residual current protector configuration is unreasonable. Some distribution transformers are not equipped with protectors. Some of them are protected by human intervention even though they are equipped with protectors, or they cannot trip due to faulty wiring. There are also cases where the operator does not operate in accordance with the technical guidelines during operation, and the protector is damaged due to operational errors. .

(3) The distribution transformer is damaged due to a short circuit to the ground or phase to phase. The low voltage side of the distribution transformer is earthed or phase-to-phase short-circuited. The short-circuit current acts on the high-voltage winding. High temperature and large mechanical stress are generated inside the winding, resulting in compression of the winding. The stress also disappears after the short-circuit fault is removed, and the winding repeats many times. Due to the mechanical stress, the insulating plastic beads, pads, etc., will loosen and fall off. The iron splint bolts will also loosen, and the high-voltage windings will be distorted or cracked, which will cause the distribution transformer to burn out in the event of a short circuit.

(4) Lightning overvoltages bring great harm to distribution transformers. Most of the high and low voltage lines of distribution transformers are introduced by overhead lines. According to the regulations, qualified arresters must be installed on the high and low voltage sides to reduce lightning overvoltage, ferromagnetic resonance overvoltage, ground fault or interphase short-circuit transformer, coils and sleeves. The hazard of the pipe. There are three reasons for lightning damage caused by lightning overvoltage: First, arrester installation and test do not meet the requirements; Second, arrester in the long-term operation due to disrepair, resulting in disconnected ground or poor contact, when lightning overvoltage When the system is over-resonant, the distribution transformer cannot be punctured because it cannot be discharged in a timely manner. Third, only the installation test of the high-voltage side arrester of the distribution transformer is emphasized, and the installation test of the arrester on the low-voltage side is scrutinized, or the low-voltage side The arrester is not installed at all, causing damage when the low voltage side of the distribution transformer is struck by lightning.

(5) The long-term overload operation caused the distribution transformer to burn out. The user's capacity increases, but the corresponding distribution transformer has not been increased in time, and the three-phase load is unbalanced. The long-term overload operation of the distribution transformer causes the internal parts of the transformer to deteriorate and burns the transformer.

2. Preventive Measures (1) Strengthen inspections of equipment, reasonably configure protection, and maintain management and maintenance in place.

(2) In the operation of the distribution transformer, it is found that the fuse should be replaced in time after it is burned. Test the load and analyze the cause. High-pressure side melt configuration: 1Distribution transformer with capacity above 100kV•A, with melt of 1.5~2.0 times rated current: 2Distribution transformer with capacity of 100kV•A and below, with 2.0~3.0 times of rated current Melt. The low pressure side melt should be selected slightly larger than the rated current.

(3) Measured at peak load for each distribution transformer load current. When the temperature is high from June to September each year, an infrared thermometer should be used to measure the temperature of the distribution transformer body, high and low voltage terminals, lightning arresters, and high- and low-voltage circuit breakers. Discover high-temperature parts or components to check in time, analyze the causes and repair. If the three-phase load distribution transformer is unbalanced, it is necessary to timely and reasonably adjust the load. The long-term overloaded distribution transformers must be timely scaled up. For the temporary power supply lines, construction and acceptance must be carried out according to the corresponding technical specifications.

(4) Adhere to preventive tests. Before the thunderstorm season every year, test and test the arrester; regularly check whether the arrester grounding line is good, whether the lead wire used in the grounding is broken or disconnected, and measure the grounding resistance with a grounding resistance meter: Those with a distribution transformer capacity of 100 kV•A and above shall not Above 4Ω, the capacity of 100kV•A or less must not exceed 10Ω. Periodically test the distribution transformers according to the regulations and find that the defects are dealt with in time.

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