The Influence of Digital Communications in Protection Schemes

Transmission lines are supervised by Intelligent Electronic Device (IED) designed to detect and clear internal faults selectively, at high speed. As the complexity of electrical power systems increase, the demands on the protective devices are also more challenging. A variety of communication schemes which complete the protection schemes have been developed and they are based on the exchange of logical data between the transmission line ends. This supplements the locally available data, confirming that a fault detected at one end in forward direction, is internal to the line, using the information from the other end/ends where protection had also detected a forward direction fault [1]. In this context, the aim of this article is to show the influence of digital communications for protection schemes on a proposed network area in the Romania power system. The studied transmission line is a short line therefore, according to [2] and [3], the protection scheme has both current differential protection as main protection and distance protection as back-up. Several fault scenarios were computed and tested in a platform that has designed the entire 400/220/110 kV transmission and distributions network of the Romanian power system is designed. The results conduct to proposed protection grading plan. Communication between the protection devices represent the basis for fault detection in the case of current differential protection or ensure fast tripping and selectivity requirements in distance protection.