Wave propagation differential protection scheme for VSC-HVDC transmission systems

Abstract

In this paper, an improved differential protection scheme is proposed for VSCHVDC transmission systems. It is based on comparing the relative conditions of the propagating waves along the power cable (or overhead line) at its terminals. A communication scheme is needed for transferring the data between both cable/line ends. The monitored signals at each line terminal are correlated to its preceding states at the other end. In this correlation, the time span between the monitored signals at both terminals is the travelling wave time along the power cable/line segment. The communication delay is not considered as an issue for HVDC power cables, because the communication system is faster than the travelling waves through the power cable. However, a considerable communication delay may be involved in case of overhead power lines. The performance of the proposed scheme is investigated with different converter types and transmission system configurations. Its security is also tested under different healthy disturbances and severe faulty conditions. The results corroborate the high efficacy and perfect security of the proposed scheme for protecting the VSCHVDC transmission systems.