Status of 5MW inductive storage facility at Soreq NRC

Abstract

A laboratory repetitive inductive storage power supply (IPS) for the ignition of an electrothermal chemical (ETC) gun is described. Eight years ago, it was designed for delivering to an ET load the energy of 500 kJ in a shot. This paper gives an updated status of this facility. The IPS is battery-based. Originally, the battery had a peak power of 5 MW and was able to charge a cylindrical coil to 700 kJ. The batteries degradation during the years was observed and documented. Fringe fields of Brooks-type coils with and without screens were analyzed. A conclusion is drawn that a screen of reasonable weight cannot reduce the stray field below a susceptibility level of electronic devices that should be shielded individually. A major facility improvement was in the field of switching. A compact hybrid repetitive opening switch (HOS) rated 50 kA, 7 kV was developed. This HOS can be used in long-charge inductive storage systems that look promising for many applications, such as uninterruptible power supplies, driving ET loads, protection of DC circuits, etc. The HOS design and testing is given in detail. The design limitations and trade-offs are discussed. A commercial vacuum circuit breaker serves as the first stage. It provides the high-current carrying capability during the inductor charge. At a desired moment, it is opened, and the current is transferred to the second stage comprising two gate commutated thyristors (GCTs) connected in series; they break the current during several microseconds. A pause of l-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 was developed. It comprises the inverse current injection into the second stage assisted by a precisely timed gate turn-off. The main benefit of this technique is the reduction of the quantity of the semiconductor devices in the second stage.