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A protection system with alternative sensing levels of the fault currents

A neutral beam injection system with pulse-type ion source was developed in Korea Atomic Energy research Institute for the Korea Superconducting Tokamak Advanced Research (KSTAR). Design requirements for the ion source were a 120 kV, 70 A ion beam with a 300 s pulse-on and 30 min. pulse-off periods. For the operation of this ion source, an acceleration power supply with the DC output ratings of 120 kV, 70 A is used. During the pulse-on periods, the maximum input current of a 22.9 kV ac lines for the acceleration power supply is higher than 200 A and the pulse-off periods, current is nearly 0 A with the main circuit breaker normally on condition. In the power distribution system, the sensing level of the fault current is higher than 200 A all the time, so in the non-operating periods of the ion source, the sensing level of the fault current is too high to accomplish a good protection sensitivity. In this paper, we propose a protection system with the variable sensing levels of the fault currents, that is, the sensing levels of the fault currents are varies with pulse-on and pulse-off periods.