Logic based Detection of Negative Sequence Currents for Six Phase System

摘要

The demand for power is increasing day to day and is becoming prime requirement. Multi phase system plays an important role in this regard and Six phase system is the most feasible alternative solution as it can increase the power transfer capability by 1.732 times with existing corridor and right-of-way and with the same phase voltage. Six phase transmission has other benefits also like greater reliability, higher efficiency and better regulation etc. In this paper the authors proposed a scheme to detect the negative sequence currents for three phase system and extended the same to six phase system. From the waveforms of negative sequences currents it is observed that at no time do all the three phase currents are positive or negative. Simultaneous positive occurrence of negative sequence three phase currents can be done by shifting any one phase by 180°. This scheme was simulated using MATLAB. The logic to detect the negative sequence currents is discussed. The results obtained in this simulation are up to the expectations. We use the platform SIMULINK of MATLAB software. Various blocks available in SIMULINK are used. Negative sequence relay is suggested to protect the Six phase system, since in our earlier studies of fault analysis on six phase system it had been observed that in certain cases of six phase faults involving ground, the zero sequence currents were found to be absent which prevents the operation of earth fault relays. Except for symmetrical faults all other faults do possess negative sequence currents which can be used for protection.