A centralized protection scheme based on combined positional protection techniques

This paper presents a new protection scheme for high-speed protection of transmission lines, the Integrated Positional Protection scheme. The concept of integrated protection is firstly introduced, in which a centralized protection relay provides the protection for multiple transmission lines. The proposed scheme is based on a specially integrated relay unit, which is installed at each substation of a network and responsible for the protection of all the line sections associated with the substation. The relay based on the detection and processing of fault generated high frequency transient current signals incorporates two novel protection principles and their application techniques, which are the positional protection techniques with and without the synchronization of Global Positioning System (GPS) respectively. The technique without the need for GPS synchronization is a non-unit protection technique, which does not require a communication link. The decision to operate is based on the detection of the relative arrival times of these high frequency components at the relay location as they propagate through the system. The basic principle of the GPS based technique is to detect the fault generated high frequency transient signals and record the time instant corresponding to when the initial travelling wave generated by the fault arriving at that busbar. A communication gateway is used to transmit and receive coded digital signals of the local information to and from the associated relay(s) in the system. At each substation, the relays determine the location of the fault by comparing the GPS time stamps measured locally with those received from the adjacent substations. Simulation studies of the scheme were carried out to examine the response to different power system and fault conditions. Results show that the scheme is insensitive to fault type, fault resistance, fault inception angle and system source configuration, and is able to offer both very high accuracy and speed in fault detection.