When conducting electrical fast pulse group testing, there is a port such as L.N and PE, where PE and Earth are two separate concepts, and electrical fast pulse group interference has common mode properties. In the experimental setup diagram provided by the standard, it can be seen that the signal cable core is added to the corresponding power lines (L.N and PE) through optional coupling capacitors, and the shielding layer of the signal cable is connected to the outer shell of the coupling/decoupling network. InEFTDuring the testing process, there are L.N and PE ports. PE and Earth are two different concepts. Electric fast pulse interference has common mode properties. In the experimental setup diagram provided by the standard, it can be seen that the signal cable cores from the experimental generator are added to the corresponding power lines (L.N and PE) through optional coupling capacitors. The shielding layer of the signal cable is connected to the casing of the coupling/decoupling network, and the casing is connected to the reference grounding terminal.

Pulse group interference is actually between the power line and the reference ground, so the interference on the power line isCommon mode interferenceFor the experiment of coupling clip, the electric fast pulse will pass through the coupling plate andTest cableThe distributed capacitance between them enters the test cable, and the pulses received by the test cable are still relative to the reference floor.

Therefore, the interference of the coupling clip on the test cable is still common mode. Once the nature of the interference is determined, we can take corresponding measures to ensure that the equipment passes the experiment smoothly. Therefore, it is not difficult to see that the X-capacitor mode capacitor used in the power filter has no inhibitory effect on EFT interference.

If the device has a metal casing, the Y capacitor (common mode capacitor) will be activated to bypass the high-frequency EFT to the casing, and then pass it between the device casing and the reference grounddistributed capacitanceReturn the signal source to avoid entering the circuit.

According to foreign scholars' research on the mechanism of equipment failure caused by pulse group interference, single pulse energy is small and will not cause equipment failure. However, the pulse group interference signal charges the capacitance of the equipment line junction. When the above energy accumulates to a certain extent, it may lead to misoperation of the line (or even the system).

Therefore, there will be a time process for line errors, and there will be a certain degree of randomness (the interval cannot be guaranteed, the line must be incorrect, especially when the test voltage approaches the critical point). It is difficult to determine whether the device is more prone to failure if pulses are applied separately or together. It is also difficult to draw the conclusion that the device is more sensitive to positive and negative pulses.

Practice has shown that a device is usually a cable that is particularly sensitive to a certain polarity at a certain test voltage. Experiments have shown that signal lines are more sensitive to fast pulse interference than power lines.

Firstly, let's analyze the interference injection method: The EFT interference signal is coupled to the main power line through a 33nf capacitor in the coupling decoupling network (the signal or control cable is interfered through a capacitor coupling clip, with an equivalent capacitance of 100pf). For a 33nf capacitor, its cut-off frequency is 100k, which means that interference signals above 100kHz can pass through; The cut-off frequency of a 100pf capacitor is 30m, allowing only interference above 30mHz to pass through. The interference waveform of the electric fast pulse is 5ns/50ns, with a repetition frequency of 5k, a pulse duration of 15ms, and a pulse group repetition period of 300ms. According to the Fourier transform, its spectrum consists of discrete spectral lines ranging from 5k to 100m, with the distance between each spectral line being the repetition frequency of the pulse.

Knowing the above points, interferencecoupling capacitorPlays the role of a high pass filter, as the impedance of the capacitor decreases with increasing frequency, low-frequency components in the interference will not couple to the EUT, only high-frequency interference signals will enter the EUT. When we add common mode inductors in EUT circuits (especially when the common mode inductors must be added to the main power line and its return line to attenuate interference), some high-frequency interference components can be attenuated because the inductance impedance increases with frequency. Therefore, the actual interference signal applied on the electric fast pulse train is only the intermediate frequency part.