Experimental investigations of surge protection devices

Abstract

Impulse interferences in AC and DC power supply systems, as well as in control and indication circuits may cause equipment damage or malfunctions of automated process control systems and other systems essential for ensuring reliable operation of facilities; they may also give rise to emergencies. To limit impulse interferences, special protection devices (diodes, varistors, and filters) are used. However, these devices do not always show sufficiently reliable performance. Typical cases in which protection devices of various types failed to protect the equipment are pointed out. To clarify why these devices showed unreliable operation, their experimental investigations were carried out by applying impulse overvoltages to them. The performance characteristics of different surge protection devices (SPDs) were studied using a combined generator producing standard 1.2/50 μs voltage impulses. When the SPD comes in action, an 8/20 μs current impulse flows through it. The maximum current amplitude may reach 30 kA, the transferred charge is 0.51 C, and the specific energy is 25.5 kJ/Ω. A damped oscillatory wave generator was used in the experiments, which produced voltage impulses with the amplitude ranging from a few hundred volt to 20 kV and frequency from 10 kHz to 1 MHz. It has been found from the experimental investigations of SPDs for electrical installations with rated voltage levels up to 1 kV and 6—10 kV that, in order to ensure efficient and reliable performance of SPDs, the amplitude-frequency characteristics of surge overvoltages shall be taken into consideration, and the protection device installation places shall be properly selected. If an SPD of a certain type is unable to ensure proper protection, a combination of different SPDs should be used. Combined application of a gapless surge arresters and diodes implies the need to coordinate their characteristics. This is achieved by connecting the diodes and the gapless surge arrester through a decoupling induction coil. In so doing, the length of connecting conductors shall be kept to a minimum. Even a relatively low inductance (a few μH) may significantly degrade the SPD surge limiting capability.