System back-up protection-a new approach

In a high voltage transmission network, fast and discriminative main protection systems are essential on order to maintain the required power system stability. As complete reliability of any main protection system is not possible, failures of the protection systems or associated circuit breakers must also be considered. To safeguard against these failures, some form of back-up scheme is required to supplement the main protection system. Because of the conflicting `speed´ and `discrimination´ requirements, the back-up protection is seldom adopted on a system-wide basis in the transmission network. With the technological advancement in relays, more sophisticated static electronic relays are available and a better approach to provide the system back-up protection is therefore possible. The authors describes in detail the requirements and application techniques to achieve an effective system back-up protection