The meaning of 8/20μs waveform

Expansion 1:

10/350μS: The typical lightning current curve for electric breakdown of the earth, which is the current curve of lightning directly attacking power lines and lightning rods, and is generally called direct lightning waveform (generally first-level protection);

8/20μS: The current curve of electromagnetic pulse induced overvoltage breakdown and burned equipment caused by typical lightning breakdown on the ground, generally called the induced lightning waveform (generally secondary protection);

According to theory, 10/350 and 8/20 under the same lightning current, the ratio of 10/350 and 8/20 lightning joule energy is 17.5:1.

1.2/50% 8/20μS combined wave: 1.2/50μS is the open circuit voltage waveform, 8/20μS is the short-circuit current waveform; for the low impedance test product: the combined wave generator analog output 8/20μS waveform, can be used as an impulse current generator ; For high-impedance test products, output 1.2/50μS waveform, which can be used as an impulse voltage generator; in low-voltage systems, in order to test surge protectors, the relevant standards propose the use of mixed waveforms to simulate lightning electromagnetic pulses, which are mainly based on Two considerations:

1) In some cases, the impedance of the test product may be unknown, and the internal impact protection component of the test product acts, causing clamping or short-circuiting, or insulation flashover, component breakdown, etc., which will cause the impedance of the test product to change under the impact of the impact. It is difficult to use a single impulse voltage or impulse current to fully test its characteristics;

2) For electromagnetic pulses caused by lightning strikes, open circuit voltage and short-circuit current are only two different aspects of the same phenomenon. When the test product changes from high resistance to low resistance in a real electromagnetic pulse environment, the original impact The voltage is immediately converted into an impulse current, that is, impulse voltage and impulse current are just different manifestations of the same thing, and they will be transformed into each other through the load condition of the equipment;

Due to the above two situations, when testing surge protection devices, it is believed that the mixed waveform can well reflect the actual situation of lightning electromagnetic pulses in the low-voltage system. When the impedance of the test product changes during the test, the impulse voltage and The inrush current will be automatically converted, which can better evaluate the performance of the test product.

Expansion 2
Chinese introduction: GB/T 16927.1-1997 [1] High voltage test technology Part 1: General test requirements National standard (GB) GB/T 16927.1-1997 This standard specifies the terminology used, the general test procedures and test products Requirements, test voltage and current generation, test methods, test results processing methods and test criteria for eligibility.