An adaptive noncommunication protection for distribution systems

This paper presents an integrated accelerated protection scheme for distribution systems based on the conventional directional overcurrent (OC) protection. An integrated relay in a distribution substation, connected to both the incoming and outgoing lines associated with the station busbar, is responsible for the protection both line sections. The increase in the operating speed is achieved by identifying the remote circuit breaker through the changes of the local currents and voltages. As a result, a significant increase in the operating speed can be achieved for the relay on the side with the longer definite grading time setting. Extensive tests have been conducted using a real-time digital simulator (RTDS) modelling a typical multi-section distribution system. The results prove that the new scheme is able to significantly increase the speed of responses of conventional time grading protection. Furthermore, the scheme not only has good adaptive capacity to source condition change, but also can clear the fault from both ends of the line section especially in single source systems, thereby improving distribution automation.