SPD response to internal generated neutral to earth transient in low voltage system

Abstract

It is essential to have a steady and continuous power supply without halting due to the false triggers to ensure continuity in activities and convenience of users especially when they are dealing with sensitive equipment. It is also vital to protect the sensitive equipment from disturbance to ensure maximum lifespan. In this country, the awareness of protecting sensitive equipment from premature malfunction due to surge overvoltage is increasing with the use of widely implemented Surge Protective Device (SPD). In reality, besides atmospheric surge overvoltage, another surge namely neutral to earth transient is also threatening sensitive equipment and cause nuisance Residual Current Device (RCD) tripping if the magnitude of the overvoltage exceeds a specific figure. The neutral to earth transient is a low magnitude transient that can go up to 250 V. Factors known to contribute to the neutral to earth transient event is related to load switching activities and wiring problems. However, this kind of disturbance is less considered in low voltage distribution system although the frequency of the occurrence isliterally higher than atmospheric overvoltage. In this research, the characteristic of typical SPD circuit under the presence of neutral to earth transient is analysed to ascertain its capability in diverting the impulse voltage. Also, to understand the operation of the voltage-limiting device in the presence of surge. The analysis has been carried out by modelling and simulating the typical SPD circuit using Microcap software. The typical SPD circuit was simulated by applying 6 kV lightning impulse voltage of 1.2/50 μs, and neutral to earth impulse voltage of 1.2/20 ms from 250 V to 750 V. The 250 V input voltage represents the neutral to earth transient. The purpose of simulating the other two input voltage is to observe the behaviour of the protective clamping device in the presence of different surge level. The output voltage has been measured, and it is found that the SPD cannot clamp the 250 V neutral to earth transient. Therefore a hybrid surge protection circuit is proposed to limit the low amplitude neutral to earth transient. The proposed surge protection circuit can limit both normal mode (L_N) and common mode (L-E, N-E) transient.