Reaction of surge protection devices on overvoltage signals with different steepness

Surge protection devices are designed and tested for an overvoltage limitation that can appear on the power line at a direct lightning strike to the power lines or a near strike because of an inductive coupling. This lightning pulse is characterized by a great destructive power. The comparison of operation of different overvoltage protections by this surge voltage stress can be found in scientific publications. This paper is focused on analysing the behavior of elements of the overvoltage protection, by the different stress voltage than the surge impulse. Modern protection devices act fast enough to eliminate or at least suppress pulses shorter than lightning or switching pulses. The first type of such a signal is EFT — Electrical Fast Transient (Burst signal). The Burst Signal simulates surges generated in the network during fast switching operations. It is characterized by a great steepness and a high repetition rate. The energy of these pulses isn't usually high enough to destroy the equipment, but they can easily disturb the internal useful signals. Another type of overvoltage pulse is very fast and dangerous and can be formed directly by electrical appliances. This is an electrostatic discharge (ESD). The electrostatic discharge is often generated by touching the casing of the device. ESD can get through the inductive and capacitive coupling to the power circuits of the device or by a direct physical touching to the uncapped power wire. ESD achieves high levels of voltage at low pulse energy. All these signals were applied to a gas discharge tube, metal oxide varistors, bipolar and unipolar TVS diodes. Their behavior was evaluated by passing the test signals, specifically the current flowing through the protection device to the ground, the residual voltage and the reaction time to the test signal. The time dependence of these variables was recorded using an oscilloscope.