Phase comparison techniques for transmission line protection

A transmission line is the most important & integral part of a power system. Due to occurrence of more than 80% of disturbances or short circuit faults in an overhead line, this section has become the most vulnerable part of the electrical system. The differential protection one of the main protection of the transmission line which trip immediately under fault condition. This paper recommends a detail theory about working principle of differential protection & differential relay design for a 400kv transmission line. The simulation results of MATLAB show that the design relay can be used as a main protection scheme for the 400 kv transmission line. This paper presents improved phase comparison technique & cosine function which is notable form of differential protection which compares the phase angle of end currents of transmission line & are able to discriminate the faulty phase accurately using equivalent π model of transmission line. The new technique can successfully differentiate between internal & external faults.