Problems and solutions for microprocessor protection of series compensated lines

Protection of systems with series compensated lines is considered to be one of the most difficult tasks for relay manufacturers and utility engineers. Protection and control of surrounding circuit elements, particularly transmission line protection, needs to be adapted to the variations introduced by these devices. Fixed series capacitors and thyristor controlled devices introduce harmonics and nonlinearities which adversely impact the protection function. To take full advantage of the series capacitor installation in a utility network, it is necessary to explore the impact of series capacitors on protection and implement appropriate schemes. This paper describes practical issues related to microprocessor based protection of power networks with fixed and controllable series compensating devices. Phenomena that affect the protection of a network with series compensated lines are explored. The paper also presents solutions and new concepts in protection and fault location for series compensated power networks.