Design aspects of thyristor protected series capacitor systems (TPSC)

Summary form only given as follows. Series capacitors in transmission lines are protected against overvoltages by employing different techniques. Arc-gaps with damping circuits have been used in the past with limited success due to their poor maintenance, inaccurate firing and arc erosion. Nowadays, MOV arresters are widely used to limit the transient overvoltage across the capacitors together with the mechanical by-pass switch that is employed only in case of permanent faults. This, however, may lead in many cases to huge amounts of MOV energy ratings that also need to be dissipated. This, in turn, results in large housing requirements and delays due to long cooling down times. With the advances achieved in thyristor technology, it is now possible to economically provide the same level of capacitor protection with smaller housing and fast cooling down times. The scheme can also be upgraded to full TCSC operation at a later stage. The paper presents the effect of the different fault strategies on the design aspects of the LTT thyristor valve. The novel features of the scheme are illustrated in light of the installation in the SCE transmission system at Vincent.