This paper presents a design of non-directional overcurrent relay micro-controller-based having the advantages of low cost, high performance and can be totally manufactured by local manufacturers. The proposed overcurrent relay can be employed to protect feeders of distribution systems for overcurrent and earth fault protection. Also, the proposed relay is considered a high speed overcurrent relay, thus it can be used for restricted earth fault applications. The main hardware platform is designed and tested with pickup accuracy not more than 0.001In and total scan cycle not more than 1ms which make this relay very accurate and adequate for fast tripping applications. . The relay has the capability to treat the incoming analogue signals of voltages and currents via the Discrete Fourier Transform (DFT) through the designed main hardware platform. In this way if the relay protects a distribution power transformer, it can detect the inrush conditions via the second harmonic detection. Also it can detect the over excitation via the fifth harmonic calculations to block the abnormal tripping for more reliable and secure distribution systems. |
