Fault detection based on ROCOV and ROCOC for multi-terminal HVDC systems

Local measurement based algorithms are mostly used for fault detection in HVDC systems since communication based algorithms are limited by the communication time delay and, therefore, they are not appropriate for long transmission distances. This paper proposes a local measurement based protection system for multi-terminal HVDC systems. Primary protection is based on rate of change of voltage (ROCOV) algorithm, while the backup and busbar protections are based on rate of change of current (ROCOC) algorithm. The performance of these algorithms is tested through simulation in PSCAD software. The proposed system is validated with different fault case scenarios, including low and high resistance fault conditions. The ROCOV algorithm provides the protection system of a fast, reliable and accurate primary protection against low and high resistance fault conditions. Meanwhile, the ROCOC algorithm is implemented in order to operate in case of primary protection failure. Its operation against low resistance faults is similar to the ROCOV performance, however, it presents low sensitivity to high resistance fault conditions. An overcurrent feature is implemented in order to improve the backup protection sensitivity and reliability. On the other hand, the busbar protection performance is fast, accurate and selective; it does not misdetect link faults.