Experience and problems with the protection of series compensated lines

The authors discuss the experience of Eskom in protecting series compensated lines starting with the original type 1 scheme consisting of permissive over-reaching and electromechanical impedance techniques. As more lines were constructed type 2 protection, consisting of electronic relays using sequence component operating and restraint quantities, was implemented. In 1985 a program was started to replace type 1 with type 3 protection, electronic phase and ground hybrid directional comparison protection. The main problem to be overcome, subsynchronous resonance, is also discussed. The series capacitors used in the capacitor banks and their operation are described