IEC 61000-4-5
In an electrical installation, disruptive surges can appear on power and data lines.
It necessitates the test of surge immunity in electrical or electronic equipment.
IEC 61000-4-5 defines test set-up, procedures, and classification levels.
Although this standard is designed for testing equipment as a whole at system level, not for individual protection devices, in practice this surge waveform is often also used for rating Transient Voltage Suppressors (TVS), Gas Discharge Tubes (GDT), Metal Oxide Varistors (MOV), and other surge protection devices.
Subsequently, the surge is transmitted into a port of the Device-Under-Test (DUT) via a coupling network.
The surge is defined by the Combination Wave Generator's open-circuit voltage and short-circuit current waveforms, characterized by front time, duration, and peak values.
With an open circuit output, the surge voltage is a double exponential pulse in the form of
With a short circuit output, the surge current waveform is a damped sine wave.
Alternatively, for outdoor telecommunication networks that experience a higher surge level, the standard also defines a more energetic generator with a 10/700 μs voltage waveform and a 5/320 μs current waveform.
[2] Thus, these waveforms are also defined by IEC 60060-1 "High-Voltage Test Techniques" and other standards in this context.
The "1.2/50 μs" generator is designed for insulation testing, and produces a high-voltage, low-current impulse into a high-impedance load.
[2] In addition, both standards have different waveform tolerances[6] and other technical requirements.
[5] When a Coupling Network is used, past experience has shown inconsistent waveforms between different generators.
3 is that a Combination Wave Generator must be verified only with a 18 μF capacitor attached at the output.
If the generator is to be designed without the coupling capacitor in mind, the output would no longer be standard compliant.
This allows one to use the built-in measurement feature on an oscilloscope, simplifying test procedures.
Initially, the switch is open, a high voltage source charges the energy-storage capacitor
The switch is then closed to deliver an impulse from the capacitor to the load through a pulse-forming network, which consists of a rise time shaping inductor
A complete circuit analysis of the ideal surge generator, including design equations and component values, is available in the presentation Introduction To Voltage Surge Immunity Testing by Hesterman et, al.[8] An updated derivation for the Third Edition is given in the paper Elementary and ideal equivalent circuit model of the 1,2/50-8/20 μs combination wave generator by Carobbi et, al.[7] The following design equations are derived by Carobbi et, al.
's waveform (including its front time and duration) while varying this ratio, the solution is found to be
An extra 18 μF series coupling capacitor has almost no effect on the open-circuit voltage, but affects short-circuit current significantly.
Carobbi et, al. suggested the following iterative, trial-and-error design procedure to take the effect of the series coupling capacitor into account.
Then, the target waveform parameters for the numerical solver are "pre-distorted", obtaining a new set of component values (by changing front time, duration, and effective output impedance).
[7] Both sources showed that it's not possible to exactly meet the waveform requirements without violating the 30% short-circuit current overshoot limit.
al. presented an approximate solution by adjusting the waveform parameters within tolerance.
[7] Also, IEC 61000-4-5 states that there's no overshoot or undershoot requirement at the output of a coupling network.
These solutions are only valid for an ideal generator, suitable for circuit simulation.
It can be used as a starting point of practical generator design, but component values have to be adjusted further due to switch non-idealities.
The following table shows the peak open-circuit voltage and short-circuit current of the Combination Wave Generator.
Depending on the test setup and port type, an additional resistor may be used as a part of the coupling network to reduce the peak surge current into the DUT, raising the output impedance to 12 Ω or 42 Ω.
