Surge voltages caused by natural lightning or man-made switching transients are a very common and usual phenomenon. IEC/EN 61000-4-5 was introduced to standard the overvoltage into the power grid, which describes the test and measurements techniques for the immunity caused by overcurrent or overvoltage. A simplified electrical diagram of the surge (1.2/50μs 8/20μs combination wave) generator is shown as below.
The ratio of peak open-circuit output voltage to peak short-circuit current at the same output
port of a combination wave generator shall be considered as the effective output impedance.
For this generator, the ratio defines an effective output impedance of 2 Ω.
Relationship between peak open-circuit voltage and peak short-circuit current
Waveform of open-circuit voltage (1,2/50 µs) at the output of the generator with no CDN connected
Waveform of short-circuit current (8/20 µs) at the output of the generator with no CDN connected
