Abstract
This study focus on the interruption capability of the DC circuit breaker employing a current commutation approach and evaluates the two main factors that determine the success rate for breaker current interruption, namely the current slope di/dt before current zero and the rate of rise of the transient recovery voltage dv/dt across the mechanical breaker contacts after current zero. A vacuum circuit breaker is used to evaluate DC breaker characteristics. Detailed mathematical and graphical analysis are presented for the proposed circuit operation used in analysing the circuit breaker properties, with simulation and experimental results at fault current levels up to 330 A.
Highlights
Current interruption in a direct current (DC) system is more difficult than in an alternating current (AC) system due to the absence of a natural current zero (CZ)
To avoid system damage due to the effects of excessive currents, an metal oxide varistor (MOV) was connected across the vacuum CB (VCB) and a series diode was located before capacitor bank (Cbank = 7 mF) to block currents flowing back into the DC source
An active commutation test circuit is proposed in this paper to investigate VCB properties in terms of varied interruption current, di/dt, dvVCB/dt and arcing time
Summary
Current interruption in a direct current (DC) system is more difficult than in an alternating current (AC) system due to the absence of a natural current zero (CZ). Asea Brown Boveri Ltd (ABB) has proposed a hybrid DC breaker to fulfil high-voltage DC (HVDC) grid requirements [10, 11] This new hybrid configuration has negligible on-state power losses and provides current interruption capability within 4 ms, at 70 kV. Proactive control of the hybrid HVDC breaker is utilised to compensate for the time delay of the fast disconnector Another method [12,13,14,15] to produce CZ in the mechanical switch involves current oscillation. Since the current oscillation involves an arc situation, the vacuum interrupter becomes the prefer building block for HVDC circuit breakers (CBs) due to its excellent insulating properties after the CZ This is not the approach proposed by ABB in [10].
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