|Application of digital technique in domestic protection system
Electric power systems -- Protection
Hong Kong Polytechnic University -- Dissertations
Department of Electrical Engineering
|vii, 84 leaves : ill. (some col.) ; 30 cm
|This project involves software simulations of microprocessor(uP)-based residual current devices (RCDs) and uP-based Miniature Circuit Breaker(MCB) integrated with RCD. Electromagnetic Transient Program (EMTP) was employed to simulate the abnormal and fault signals generated from the circuit. Trip signal will be activated if the leakage current or overcurrent exceeds the specified limit. A domestic system with one incoming source was simulated using EMTP to study the u-RCD and the u-MCB integrated with RCD. The signals are sampled at 4 kHz and the digital signals were analysed by Full Cycle Fourier Algorithm. The purpose is to simulate a 5A current rating u-MCB integrated RCD with 3OmA sensitivity. The leakage response of RCD is 30-200 mA in lOOms and above 200mA in 40ms. The current/time characteristic of u-RCD was found to be satisfactory by comparing with IEE regulations. The u-MCB integrated RCD was tested under various types of faults including earth leakage, single phase to earth fault, line to line fault, double line to earth fault and three phase fault. The results are satisfactory and it is able to distinguish between leakage fault and over current fault. In conclusion, these microprocessor based circuit breakers provide multitude of time/current characteristics. It provides a flexibility to grade with several different protective devices and a positive contribution towards the solution of discrimination.
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