How to choose a power surge arrester to achieve graded protection
May 23, 2022
First of all, you must figure out your own power distribution system, is it TT, TN or IT system? Because the power distribution system is determined, we can determine the single-phase, three-phase, wiring method, etc., so as to choose the appropriate lightning protection products. Most of the power distribution systems in my country are in the TN-S mode.
The main material in lightning protection products is zinc oxide varistor. The quality of its material and the level of craftsmanship have a direct impact on whether the product can produce the expected protection when it is struck by lightning, so you must choose a lightning protection device. Understand the source of the manufacturer's varistor.
The important parameters of the power surge arrester:
Nominal voltage Un: The rated voltage of the protected system is consistent. In the information technology system, this parameter indicates the type of protector that should be selected, and it indicates the effective value of the AC or DC voltage.
The maximum continuous working voltage Uc: the maximum voltage effective value that can be applied to the designated end of the protector for a long time without causing changes in the characteristics of the protector and activating the protection element.
Nominal discharge current In: The maximum surge current peak value that the protector can withstand when a standard lightning wave with a waveform of 8/20s is applied to the surge protector for 10 times.
Maximum discharge current Imax: when the protector is impacted by a standard lightning wave with a waveform of 8/20s once, the maximum impulse current peak value that the protector can withstand.
Voltage protection level Up: the maximum value of the protector in the following tests: the flashover voltage with a slope of 1KV/s; the residual voltage of the rated discharge current.
The first-level lightning protection device can discharge the 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 arrester is a protective device for the residual voltage of the previous-level lightning arrester and the induced lightning strike 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 a considerable amount of energy that will be conducted over, and a second-level surge protector is required to further absorb the surge protector. At the same time, the transmission line passing through the first-level lightning protection device will also induce the lightning strike 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 strike energy. The third-level lightning arrester protects the LEMP and the residual lightning strike energy passing through the second-level lightning arrester.
The purpose is to prevent the surge voltage from being conducted directly from the LPZ0 area into the LPZ1 area, and to limit the surge voltage of tens of thousands to hundreds of thousands of volts to 2500-3000V.
The power supply lightning arrester installed on the low-voltage side of the household power transformer 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 12.5kA (T1 test). This level of power surge arrester should be a large-capacity power surge arrester connected between each phase of the incoming line of the user's power supply system and the ground. Generally, this level of power surge arrester is required to have a maximum impact capacity of more than 12.5kA per phase (T1 test), and the required limit voltage is less than 2500V, which is called a CLASSI level power surge protector.