On line inductance and resistance calculation for transmission line protection

A proposed method of transmission line protection bydigital computer is outlined. This method is intended forapplication to short and medium length high voltage transmissionlines. The two essential elements are the derivationof a single relaying voltage and current on a three phaseline, and the calculation of the impedance of the linesection.It is shown that for all single fault types a set ofderived relaying quantities satisfy a single differentialequation. Using sampled values of voltage and current thisequation is solved numerically for the resistance and inductanceof the faulted section.Using fault data from a model transmission line andportion of a high voltage transmission system the calculationtechnique is shown to have satisfactory accuracy.The three phase scheme has been implemented in realtime using a typical process control computer. The calculationtimes and accuracies have been determined