A new relaying method to discriminate between fault and power swing condition

Distance relay may maloperate during power swing condition which can arise due to variation of heavy load and switching of adjacent loaded line. Hence, it is necessary to discriminate the fault condition and power swing condition in case of line protection. During fault on transmission line the reactive power & voltage will change drastically compare to power swing condition. This paper demonstrates a new method based on rate of change of reactive power and rate of change of voltage which effectively discriminates various types of fault and power swing conditions. The derivative of line reactive power & voltage variation is calculated by utilizing local end voltage & current signals. The proposed algorithm is evaluated by simulating various disturbances on two machine system of 220 kV network in PSCAD/EMTDC software package. The power swing conditions are simulated by fault isolation, change in mechanical input to turbine of generating stations, switching of heavy loads connected to bus and disconnection of heavily loaded parallel transmission line. Moreover, various types of short circuit faults are simulated on the transmission line including faults during power swing and high resistance fault. The proposed fault v/s power swing discrimination algorithm is executed in MATLAB software.