Since the energy of lightning strikes is very huge, it is necessary to gradually discharge the energy of lightning strikes to the ground through a hierarchical discharge method. The first-level lightning protection device can discharge direct lightning current, or discharge the huge energy conducted when the power transmission line is directly struck by lightning. For places where direct lightning strikes may occur, CLASS-I lightning protection must be carried out. The second-level lightning protection device is a protection device for the residual voltage of the front-level lightning protection device and the induced lightning strikes in the area. When the front-level lightning strike energy absorption occurs, there is still a part of the equipment or the third-level lightning protection device. It is quite a huge amount of energy that will be transmitted, and it needs to be further absorbed by the second-level lightning protection device. At the same time, the transmission line passing through the first-level lightning protection device will also induce the lightning electromagnetic pulse radiation LEMP. When the line is long enough, the energy of the induced lightning becomes large enough, and the second-level lightning protection device is required to further discharge the lightning energy. The third-level lightning protection device protects LEMP and the residual lightning energy passing through the second-level lightning protection device.

1. The first level of protection

The purpose is to prevent the surge voltage from being directly conducted from the LPZ0 zone into the LPZ1 zone, and to limit the surge voltage of tens of thousands to hundreds of thousands of volts to 2500-3000V.

The power surge protector installed on the low-voltage side of the home power transformer should be a three-phase voltage switch-type power surge protector as the first level of protection, and its lightning flow rate should not be less than 60KA. This level of power surge protector should be a large-capacity power surge protector connected between each phase of the incoming line of the user's power supply system and the ground. It is generally required that this class of power supply lightning protection device has a maximum impact capacity of more than 100KA per phase, and the required limit voltage is less than 1500V, which is called CLASS I power supply lightning protection device. These electromagnetic lightning protection devices are specially designed to withstand the large currents of lightning and induced lightning and to attract high-energy surges, which can shunt large amounts of surge currents to the ground. They only provide limited voltage (when the impulse current flows through the power surge protector, the maximum voltage appearing on the line is called the limit voltage) is medium-level protection, because CLASS I protectors mainly absorb large surge currents. They cannot completely protect the sensitive electrical equipment inside the power supply system.

The first-level power lightning arrester can prevent 10/350μs, 100KA lightning wave, and reach the highest protection standard stipulated by IEC. The technical reference is: the lightning flow rate is greater than or equal to 100KA (10/350μs); the residual voltage value is not greater than 2.5KV; the response time is less than or equal to 100ns.

2. The second level of protection

The purpose is to further limit the value of the residual surge voltage through the first-stage lightning arrester to 1500-2000V, and implement equipotential connection for LPZ1-LPZ2.

The power surge protector output from the distribution cabinet circuit should be a voltage-limiting power surge protector as the second level of protection, and its lightning current capacity should not be less than 20KA. It should be installed in the substation that supplies power to important or sensitive electrical equipment. Road distribution office. These power supply lightning arresters can better absorb the residual surge energy that has passed through the surge arrester at the user's power supply entrance, and have an excellent suppression effect on transient overvoltage. The power surge protector used here requires a maximum impact capacity of 45kA or more per phase, and the required limit voltage should be less than 1200V, which is called a CLASS II power surge protector. The general user power supply system can achieve the second level of protection to meet the requirements of the operation of electrical equipment.

The second-level power lightning arrester adopts class C protector for phase-center, phase-ground and middle-ground full mode protection. The main technical parameters are: lightning current capacity is greater than or equal to 40KA (8/20μs); residual voltage The peak value is not more than 1000V; the response time is not more than 25ns.

3. The third level of protection

Principle of Surge Protector

The purpose is to ultimately protect the equipment by reducing the value of the residual surge voltage to within 1000V, so that the surge energy will not damage the equipment.

The power surge protector installed at the incoming end of the AC power supply of electronic information equipment should be a series voltage-limiting power surge protector as the third level of protection, and its lightning current capacity should not be less than 10KA.

The last line of defense can use a built-in power supply lightning arrester in the internal power supply of the electrical equipment to achieve the purpose of completely eliminating the tiny transient overvoltage. The power surge protector used here requires a maximum impact capacity of 20KA or less per phase, and the required limit voltage should be less than 1000V. For some particularly important or particularly sensitive electronic equipment, it is necessary to have the third level of protection, and it can also protect the electrical equipment from the transient overvoltage generated inside the system.

For the rectifier power supply used in microwave communication equipment, mobile station communication equipment and radar equipment, it is advisable to select a DC power supply lightning protector adapted to the working voltage as the final protection according to the protection needs of its working voltage.

4. Level 4 and above protection

According to the withstand voltage level of the protected equipment, if two levels of lightning protection can limit the voltage to be lower than the equipment’s withstand voltage level, only two levels of protection are needed. If the equipment’s withstand voltage level is low, four levels or even More levels of protection. The lightning current capacity of the fourth level protection should not be less than 5KA.