Abstract :
A two-stage thyristor circuit breaker (TCB) has been developed by British industry in conjunction with academia. The principal differences between the two-stage TCB and other types, is that is dissipates the energy stored in circuits during load switching, or fault clearance, in a controlled manner, using switched inserted resistance. The technique enables limitation of the switching voltage to twice the system voltage (2 pu) for practical systems, and permits optimisation of the ratings and cost of the TCB circuit components. A compact, withdrawable, prototype design, rated nominally at 4000 A, 700 V DC, has been extensively tested under a variety of short-circuit test conditions. The prototype TCB successfully cleared a range of fault conditions, typical of mass rapid transit systems. In all cases the overvoltage was limited to 2 Pu, as predicted by simulation studies
