Digital protection integrated distance relay

This thesis presents updated algorithm for double-circuit, double-fed transmission lines to overcome problem arises such as mutual couplingbetween the two circuits and the effect of remote source infeed. A newtechnique is proposed to compensate the effect of fault resistance indistance measurement calculations, in a specified range that related to thepositive-sequence impedance of the line.The algorithm supervises all the six currents in the conductors andthe three bus voltages. The algorithm development is based on the faultanalysis, which involve different fault types at different locations, on amathematical model line that simulates a typical double-circuit lineconfiguration, employing a standard routine. The algorithm uses the ratiosbetween the magnitudes of the currents to detect the fault after a transientdetection. A critical value of the ratio is specified which is the setting of therelay. By using this technique, the maximum value of the fault resistancethat can be detected is 170 n at 80% of the line length and this value isincreased to 730 n at relay location, which equals to 5- to 21-times positivesequence impedance of the line.To compensate the effect of the fault resistance that involves theeffect of remote source infeed, the algorithm suggests to use the angle ofthe fault current in the fault resistance equal to the angle of the zero-sequence current in the faulted circuit. With this assumption, the faultlocation can be determined accurately with a maximum error of2.5% forall detected values of fault resistance. Also, the effect of the variation of the