Substation is an important protection facility for lightning protection in power system. If lightning strikes, it will cause a large area of power failure, which will seriously affect society and people's lives. Therefore, the lightning protection measures of substation must be very reliable. (1) The source of lightning. First, lightning directly hits the equipment in the substation; Second, lightning waves formed by lightning induced overvoltage and direct lightning overvoltage of overhead lines invade substations along the line. (2) The protection of direct lightning in substation is generally solved by installing lightning rods or erecting lightning rods within a certain distance along the incoming line of substation. (3) Lightning waves formed by lightning induced overvoltage and direct lightning overvoltage of overhead lines invade the substation along the line, which is the main cause of lightning damage in the substation. If lightning protection measures are not taken, the insulation of electrical equipment in substation will be damaged, resulting in accidents. The purpose of installing lightning arrester in substation is to limit the amplitude of invading lightning wave, so that the overvoltage of electrical equipment does not exceed its impulse tolerance value, while the main purpose of installing protection section in substation incoming line is to limit the amplitude of lightning current flowing through lightning arrester and the steepness of invading lightning wave.

2 principles of installing lightning rod in substation

All protected equipment should be within the protection range of lightning rod (wire) to avoid being struck by lightning. When lightning strikes the lightning rod, the potential of the lightning rod to the ground may be very high. If the insulation distance between the lightning rod and the protected electricity is not enough, it is possible to discharge between the lightning rod and the protected equipment after lightning strike. This phenomenon is called counterattack. At this time, the lightning rod can still add the high potential of lightning wave to the protected electrical equipment, causing accidents.

3 Determination of minimum lightning protection distance between lightning rod and electrical equipment

When lightning strikes the lightning rod, lightning current flows through the lightning rod and its grounding device. In order to prevent the air gap between the lightning rod and the protected equipment or frame from being broken down and causing counterattack accidents, the air gap must be greater than the minimum safe clear distance.

4. Relevant regulations for installing lightning rod

For substations of 35kV and below, due to its low insulation level, independent lightning rods must be installed to meet the requirement of no counterattack. For substations above 1 10kV, the lightning rod can be directly installed on the frame of the distribution device because of the high insulation level of the distribution device at this voltage level, so the high potential generated by lightning strike of the lightning rod will not cause counterattack accidents of electrical equipment. The distribution frame with lightning rod should be equipped with auxiliary grounding device, and the electrical distance between the connection point of main transformer grounding device and substation grounding network should not be less than 15m. Its function is to make the high potential generated on the grounding device of the lightning arrester gradually decay during the propagation along the grounding network to the grounding point of the transformer, so that the invading lightning wave will not cause the counterattack accident of the transformer when it reaches the grounding point of the transformer. Because the insulation of transformer is weak and transformer is an important equipment of substation, lightning rod should not be installed on the gantry of transformer. Because the distance between the distribution equipment of the substation and the first tower of the substation may be relatively large, if the lightning conductor on the tower is allowed to lead to the frame of the substation, this conductor will be protected, which is more economical than using lightning rods. Due to the shunt effect at both ends of lightning rod, when lightning strikes, the potential rise caused by lightning rod is smaller than that caused by lightning rod. Therefore, the distribution equipment with 1 10kV or above can lead the line lightning rod to the outlet portal frame, but the area with soil resistivity greater than1000Ω m should be provided with centralized grounding devices. For 35 ~ 60 kV distribution equipment, in the area where the soil resistivity is not more than 500 Ω m, it is allowed to lead the lightning rod of the line to the outlet portal frame, but a centralized grounding device should be installed. When the soil resistivity is greater than 500 Ω m, the lightning rod should be terminated on the terminal tower of the line, and the lightning rod can be used for the first line protection in the substation.

The action mechanism of lightning is very complicated, and we can't completely control the occurrence of lightning damage, but we can reduce the occurrence of lightning damage through necessary lightning protection measures. In order to ensure the safe operation of power grid, we should constantly sum up experience and lessons, strengthen operation, overhaul and maintenance, attach importance to lightning protection countermeasures and technical transformation, and take targeted preventive measures.