1. Power line SPD
Since the energy of the lightning strike is very huge, it is necessary to discharge the energy of the lightning strike to the ground gradually through the method of graded discharge. In the direct lightning non-protection zone (LPZ0A) or at the junction of the direct lightning protection zone (LPZ0B) and the first protection zone (LPZ1), install a surge protector or a voltage-limiting surge protector that has passed the Class I classification test as the first The first-level protection discharges the direct lightning current, or discharges the huge energy conducted when the power transmission line is directly struck by lightning. Install a voltage-limiting surge protector at the junction of each partition (including the LPZ1 area) after the first protection zone as a second, third or higher level of protection. The second-level protector is a protective device for the residual voltage of the front-level protector and the induced lightning strike in the area. When a large lightning strike energy absorption occurs in the front-level, there is still a part that is quite huge for the equipment or the third-level protector. The energy will be conducted over, and a second-level protector will be required to further absorb it. At the same time, the transmission line passing through the first-level lightning arrester will also induce lightning strike electromagnetic pulse radiation. When the line is long enough, the energy of the induced lightning becomes large enough, and the second-level protector is required to further discharge the lightning strike energy. The third-level protector protects the residual lightning strike energy passing through the second-level protector. According to the withstand voltage level of the protected equipment, if the two-level lightning protection can limit the voltage to be lower than the withstand voltage level of the equipment, only two levels of protection are required; if the withstand voltage level of the equipment is low, four levels or even More levels of protection.
To choose an SPD, you first need to understand some parameters and how they work.
(1) The 10/350μs wave is a waveform that simulates direct lightning strikes, and the waveform energy is large; the 8/20μs wave is a waveform that simulates lightning induction and lightning conduction.
(2) The nominal discharge current In refers to the peak current of the 8/20μs current wave flowing through the SPD.
(3) The maximum discharge current Imax, also known as the maximum current flow, refers to the maximum discharge current that the SPD can withstand once using an 8/20μs current wave to impact the SPD.
⑷ The maximum continuous withstand voltage Uc (rms) refers to the maximum RMS AC voltage or DC voltage that can be continuously applied to the SPD.
⑸ Residual voltage Ur refers to the residual voltage value under the rated discharge current In.
⑹ The protection voltage Up represents the voltage characteristic parameter between the SPD limit terminals, its value can be selected from the list of preferred values, and should be greater than the maximum value of the limit voltage.
⑺ The voltage switching type SPD mainly discharges the 10/350μs current wave, and the voltage limiting type SPD mainly discharges the 8/20μs current wave.
2. Signal line SPD
The signal line SPD is actually a signal arrester, which is installed in the signal transmission line, generally at the front end of the equipment, to protect the subsequent equipment and prevent lightning waves from influxing from the signal line to damage the equipment.
1) Selection of voltage protection level (UP)
The UP value should not exceed the rated value of the withstand voltage of the protected equipment, and the UP requires that the insulation of the SPD and the protected equipment should have good coordination.
In the low-voltage power supply and distribution system installations, the equipment should have a certain surge withstand capability, that is, the impulse overvoltage capability. When it is not possible to obtain the impulse overvoltage resistance value of various equipment of 220/380V three-phase system, it can be selected according to the given index of IEC 60664-1 and GB 50057-1994 (2000 edition).
2) Selection of nominal discharge current In (impulse current capacity)
Peak current flowing through SPD, 8/20 μs current wave. It is used to do class II classification test for SPD, and it is also used for preprocessing of SPD class I and class II classification test.
In fact, In is the maximum inrush current peak value that can pass a predetermined number of times (usually 20 times) and a predetermined waveform (8/20 μs) without substantial damage to the SPD.
3) Selection of the maximum discharge current Imax (limit impulse current capacity)
Peak current through SPD, 8/20 μs current wave for Class II classification test. Imax has many similarities with In, they both use the peak current of 8/20 μs current wave to do class II classification test for SPD. The difference is also obvious. Imax only does one impact test on SPD, and SPD does not suffer substantial damage after the test; while In can do 20 such tests, and SPD cannot be substantially damaged after the test. Therefore, Imax is the current limit value of the inrush, so the maximum discharge current is also called the limit inrush current capacity. Obviously, Imax>In.
