When lightning strikes a power transmission line directly, the first-level lightning arrester may release the massive energy that is conducted as well as the direct lightning current. CLASS-I lightning protection must be used in locations that might experience direct lightning strikes. The second-level lightning arrester serves as a safeguard against both the induced lightning strike in the vicinity and the residual voltage of the first-level lightning arrester. There is still a piece of the apparatus or the third-level lightning protection device present when the front-level lightning strike energy absorption takes place. The energy that will be passed across is rather substantial, necessitating more absorption by the second-level lightning arrester.The transmission line going through the first-level lightning protection device will simultaneously cause LEMP from lightning strikes. The second-level lightning protection device is necessary to further discharge the lightning strike energy after the line is long enough and the energy of the induced lightning reaches a sufficient size. The LEMP and the remaining lightning strike energy that passes through the second-level lightning arrester are both protected by the third-level lightning arrester.
First line of defense
The aim is to limit the surge voltage of tens of thousands to hundreds of thousands of volts to 2500-3000V and to prevent the surge voltage from being conducted directly from the LPZ0 area into the LPZ1 area.
The power supply lightning arrester should be a three-phase voltage switching type power supply lightning protection device as the first-level protection, and its lightning current flow should not be lower than 60KA. It should be mounted on the low-voltage side of the home power transformer.A large-capacity power surge arrester should be installed between each phase of the user's power supply system's incoming line and the ground at this degree of surge protection. This kind of power surge arrester, known as a CLASS I power surge arrester, is often needed to have a maximum impact capacity of more than 100 KA per phase and a necessary limit voltage of less than 2500V. These electromagnetic arresters are built to resist the powerful currents produced by natural and artificial lightning strikes and to draw in high-energy surges that are then diverted to earth.
They only provide voltage limiting (when the surge current flows through the power arrester, the maximum voltage appearing on the line is called voltage limiting) as a medium level of protection, because CLASS I protectors mainly absorb larger surge currents, only they Sensitive electrical equipment inside the power supply system cannot be fully protected.
The first-class power surge arrester can prevent 10/350μs, 100KA lightning waves, reaching the highest protection standard stipulated by IEC. Its technical reference is: the lightning current flowing through 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.
Second level protection
The purpose is to further limit the residual surge voltage through the primary arrester to 1500-2000V, and implement equipotential connection for LPZ1-LPZ2.
As a secondary protection, the power arrester output from the power distribution cabinet line shall be a voltage limiting power arrester, and its lightning current capacity shall not be less than 20KA. It shall be installed in the power supply in the distribution room of important or sensitive electrical equipment. These power surge arresters can better absorb the residual surge energy passing through the surge arresters at the user's power inlet, and have excellent suppression effect on transient over-voltage. The maximum impact capacity required by the power arrester used here is more than 45kA per phase, and the required limiting voltage should be less than 1200V, which is called Class II power lightning protection device. If the second level protection is realized, the power supply system of general users can meet the operation requirements of electrical equipment.
The secondary power arrester adopts C-type protector for full mode protection of relative neutral, phase to ground and neutral to ground. The main technical parameters are: lightning current capacity is greater than or equal to 40KA (8/20 μ s）； The peak value of residual voltage shall not exceed 1000V; The response time shall not exceed 25ns.
Three level protection
The purpose is to finally protect the equipment by reducing the residual surge voltage to below 1000V, so that the surge energy will not damage the equipment.
When the power lightning arrester installed at the AC power incoming line end of electronic information equipment is used as the three-level protection, it shall be a series voltage limiting power lightning protection device, and its lightning current capacity shall not be less than 10KA.
The last line of defense is to install a built-in surge arrester in the power supply part of the electrical equipment to completely eliminate the small transient over-voltage. The maximum pulse capacity required by the power arrester used here is 20KA or less per phase, and the required limiting voltage should be less than 1000V. It is necessary to provide the third level protection for some particularly important or sensitive electronic equipment, which can also protect electrical equipment from the impact of 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 recommended to select the DC power arrester with appropriate working voltage as the final protection according to the protection requirements of its working voltage.
Grade 4 and above
According to the withstand voltage level of the protected equipment, if the two-level lightning protection can limit the voltage below the withstand voltage level of the equipment, only two-level protection is required. If the withstand voltage level of the equipment is low, it shall provide four or higher levels of protection. The lightning current capacity of the fourth level protection shall not be less than 5KA
