Signal Line Lightning Protector

Signal line SPD is actually a signal lightning arrester, which is installed in the signal transmission line, usually at the front end of the equipment, to protect subsequent equipment and prevent lightning waves from influxing from the signal line and damaging the equipment.

(1) Selection of voltage protection level (UP)
The UP value should not exceed the impulse voltage rating of the protected equipment. UP requires that the insulation between the SPD and the protected equipment should have good coordination.
In low-voltage power supply and distribution system installations, equipment should have a certain ability to withstand surges, that is, ability to withstand impact overvoltage. When the impact overvoltage values of various equipment in the220/380Vthree-phase system cannot be obtained,the selection can be made according to the given indicators of IEC 60664-1 and GB 50057-1994 (2000edition).

(2) Selection of nominal discharge current In (impact current capacity)
Peak current flowing through SPD, 8/20 μs current wave. It is used for conducting Level II classification tests on SPD, and is also used for pretreatment of Level I and Level II classification tests on SPD.
In fact, In is the maximum inrush current peak value that the SPD can pass through a specified number of times (usually 20 times) and a specified waveform (8/20 μs) without substantial damage.

(3) Selection of maximum discharge current Imax (limited impact current capacity)
Peak current flowing through the SPD, 8/20 μs current wave, for Class II classification testing. Imax has many similarities with In. They both use the peak current of the 8/20 μs current wave to perform Class II classification tests on SPD. The difference is also obvious. Imax only performs one impact test on SPD, and the SPD will not be substantially damaged after the test; while In can do 20 such tests, and the SPD will not be substantially damaged after the test. Therefore, Imax is the current limit value of the impact, so the maximum discharge current is also called the ultimate impact current capacity. Obviously, Imax>In.