A hybrid repetitive opening switch for inductive storage systems and protection of DC circuits

A compact hybrid repetitive opening switch (HOS) rated 50 kA, 4 kV is described. This HOS is intended for use in long-charge, e.g., battery-based inductive storage systems that look promising for many applications, such as uninterruptible power supplies, driving ET loads, protection of DC circuits, etc. A commercial vacuum circuit breaker serves as the first stage. It provides the high-current carrying capability of 2.5·10⁸ A²s during the inductor charge, or a 1600A continuous rating with low power losses. At a desired moment, it is opened, and the current is transferred to the second stage comprising high-power gate turn-off thyristors or gate commutated thyristors (GCTs) that break the current during several microseconds. A pause of 1-2 ms is provided for the vacuum breaker recovery. A novel approach allowing the enhancement of an order of magnitude of the turn-off capability of fully-controlled semiconductor devices, such as GCTs, is developed and analyzed. It comprises the inverse current injection into the second stage assisted by a precisely timed gate turnoff. The main benefit of this technique is a dramatic reduction (by factor of ten) in the quantity of semiconductor devices in the second stage. The electrical and mechanical design of the HOS is described. PSpice simulations coupled with field analysis of nonlinear magnetic components and test results are presented. Future development is outlined.