Protection and fault identification in presence of power swing blocking/unblocking function

Distance relaying is widely preferred for transmission line protection all over the world. However, the distance relays are badly affected by both, unstable and stable power swing. The occurrence of fault under blocking condition is a severe issue for protection engineer. A new approach for protection of transmission lines when distance relays are blocked is presented using a relatively new signal processing tool known as S transform. The energy content in the current signal is found using the S matrix. To ensure the reliability of the scheme and for the identification of fault types, it is coupled with detection of dc offset and sequence components. The reliability of the scheme is verified by simulating various fault scenarios.