Causes and prevention of damage of 10 kV gapless zinc oxide arrester

The zinc oxide arrester is sealed with silicone rubber. During operation, due to large changes in external temperature, the silicone rubber used for sealing causes cracks, shedding, cracks, etc., and some of the ends of the arrester are intruded by moisture, rain, etc., causing damage to the internal insulation of the arrester, causing aging failure of the resistor. The damage to the arrester is caused. Therefore, it is necessary to prevent damage to the arrester to reduce the impact of lightning strikes on the line.

Cause of damage

The grounding resistance value is too large. Many agricultural electricians pay insufficient attention to the design and construction of the grounding device, which often causes the grounding resistance value to be too large and does not meet the requirements of the regulations. The grounding device of the arrester is the only channel for the strong lightning current to be discharged to the earth when it is struck by lightning. The grounding resistance value cannot meet the requirements of the regulations, and the lightning current cannot be quickly discharged to the earth, causing some lightning current to reversely impact the arrester, so that the arrester Suffering serious damage, the distribution transformer may be damaged at the heaviest.

The arrester valve is aging and deteriorated. After the arrester valve is operated for a certain period of time, some of the valve plates are deteriorated and the power loss is greatly increased. The operating voltage of the power grid is basically constant, which inevitably increases the burden on the normal valve plate inside the arrester, so that it accelerates aging and deterioration. There is a vicious circle inside which eventually causes damage.

Transient, resonant overvoltage shock damage. When the arrester is subjected to transient over-voltage such as resonance, the power frequency voltage will automatically replenish the over-voltage energy, so that the over-voltage discharged from it cannot be rapidly attenuated (or even attenuated), which will cause great damage and damage. .

Precaution

Reasonably choose the grounding resistance. The grounding device of the arrester must be designed and constructed according to the requirements of the regulations according to the capacity of the distribution transformer. For the distribution of 100 kVA and above, the grounding resistance value must be less than or equal to 4 ohms; for the following distribution, the grounding resistance value is required to be no more than 10 ohms. When the weather is dry every winter (more than one week in a continuous sunny day), the grounding resistance value is tested until the requirements are met. Before the arrival of the thunderstorm season every year, the grounding down the line and the connection point are carefully checked, and the problem is immediately dealt with.

Use a good arrester. Choose the products of formal professional manufacturers with advanced technology and perfect testing means. The operating voltage of the arrester must be selected according to the installation location and operating characteristics, so that it can safely and reliably operate when subjected to atmospheric overvoltage (such as lightning strikes) and operating overvoltage, and is subject to transient overvoltage attacks and grid occurrences. Phase-to-earth fault, no malfunction when the system has the highest voltage.

It is recommended to use a zinc oxide surge arrester with a series gap in the rural 10 kV distribution network. Because of the existence of the composite gap, the arrester ensures that the valve plate is only subjected to the high voltage during the overvoltage protection action, and the overvoltage energy discharged by the valve is free of freewheeling, that is, it is subjected to high voltage The action time is extremely short. Under the normal condition of the power grid, the voltage value of the valve plate is very low due to the partial pressure of the gap resistance, thus greatly improving the operating condition of the valve plate and delaying the aging of the valve plate. , deterioration, failure.