Lightning protector is an indispensable device in the lightning protection of electronic equipment, its role is to flee into the power lines, signal transmission lines of transient overvoltage limit in the equipment or system can withstand the voltage range, or will be a strong lightning current discharge into the ground, in order to protect the protected equipment or system from the impact.
Divided by working principle
According to its working principle, SPD can be divided into voltage switching type, voltage limiting type and combination type.
(1) Voltage switching type SPD, presenting high impedance when there is no transient overvoltage, once responding to lightning transient overvoltage, its impedance will suddenly change to low impedance, allowing lightning current to pass through, also known as "short-circuit switching type SPD".
(2) voltage limiting SPD. when there is no transient overvoltage, the impedance is high, but with the increase in surge current and voltage, its impedance will continue to decrease, its current and voltage characteristics have a strong nonlinearity, sometimes referred to as "clamp type SPD.
(3) combined SPD. by the combination of voltage-switching type components and voltage-limiting type components, can behave as a voltage-switching type or voltage-limiting type or both, depending on the characteristics of the applied voltage.
Power SPD
Because the energy of a lightning strike is very large, it is necessary to gradually release the lightning energy to earth through a graded discharge method. In the direct lightning non-protected area (LPZ0A) or in the direct lightning protection zone (LPZ0B) and the first protection zone (LPZ1) junction, the installation of surge protectors or voltage limiting surge protectors through the first level of classification test as the first level of protection, the direct lightning current discharge, or when the transmission line suffers a direct lightning strike, will conduct a huge amount of energy for discharge. In the first protection zone after the partition (including LPZ1 zone) junction of the installation of voltage limiting surge protector, as the second, third or higher level of protection. The second level protector is for the residual voltage of the first level protector and induction lightning strikes in the area of protection equipment, in the first level to absorb the larger lightning strike energy, there are still some equipment or the third level protector energy is quite huge, will be conducted over, the need for the second level protector to further absorb. At the same time, the transmission line through the first level of lightning protector will also induce lightning strike electromagnetic pulse radiation. When the line is long enough, the induced lightning energy becomes larger, requiring the second-stage protector to further implement the discharge of lightning strike energy. The third level protector protects the residual lightning energy that passes through the second level protector. Depending on the voltage level of the equipment being protected, if the two-stage lightning protector can limit the voltage to below the voltage level of the equipment, only two levels of protection are required; if the voltage level of the equipment is lower, four or more levels of protection may be required.
To choose SPD, you need to understand some parameters and its working principle first.
(1) 10/350μs wave is the waveform of simulated direct lightning, waveform energy; 8/20μs wave is the waveform of simulated lightning induction and lightning conduction.
(2) The rated discharge current In is the peak current flowing through the SPD, 8/20μs current wave.
(3) Maximum discharge current Imax, also known as the maximum flux, is the maximum discharge current that can be withstood at one time using the 8/20μs current wave to impact the SPD.
(4) The maximum continuous withstand voltage Uc (rms) is the maximum AC voltage RMS or DC voltage that can be continuously applied to the SPD.
(5) Residual voltage Ur is the residual voltage value at the rated discharge current In.
(6) Protection voltage Up characterizes the voltage characteristic parameter between the SPD limiting terminals, the value of which can be selected from the list of preferred values and should be greater than the maximum value of limiting voltage.
(7) The voltage switching type SPD mainly discharges a current wave of 10/350μs, while the voltage limiting type SPD mainly discharges a current wave of 8/20μs.
