A new digital relaying scheme for EHV three terminal transmission lines

The paper describes a new technique for protecting asymmetrical and symmetrical EHV three terminal lines. One relay is installed to recognize a blocking or a tripping terminal at the terminal that uses two circuits. The polarity of fault current is detected at each end using the Haar wavelet function. A communication channel is used to receive the status of the polarity at each end. A gate logic circuit at each end is used to issue final decision based on the collected polarities. The problem areas of the current protective techniques are solved. No voltage signal is used. An EMTP/ATP simulator is used to demonstrate the performance of the proposed technique.