300 kA Test results of the 1 MA resonant series counterpulse opening switch system

At the Pulse Physics Laboratory, research is being performed to develop a counterpulse technique for the controlled interruption of very high currents in inductive storage pulsed power systems. Presently, a repetitive mechanical high current opening switch is applied to commutate current to an inductive load (for example a rail accelerator) from a storage inductor charged by a homopolar generator. To increase the current level the mechanical switch is able to interrupt, the application of a counterpulse technique and a separate closing switch looks promising. Otherwise, the arc that would occur between the contacts of the switch during opening and closing at high currents (mega-ampere level), would severely damage the contacts.
To prevent the damage caused by arcing, the current must be reduced to zero or a low level before opening the switch . To be able to achieve this, the resonant series counterpulse circuit is proposed. The circuit incorporates units consisting of a capacitor bank of electrolytic capacitors with parallel connected diodes and a thyristor connected in series. Upon command, these units will create a resonant counterpulse current through the opening switch. The net current through the switch reduces to zero and the switch is opened without damaging the contacts.
Other counterpulse circuits utilise capacitors such that they experience a voltage reversal and high initial voltages are required. The resonant series counterpulse circuit uses capacitors in such a way that they do not experience a voltage reversal and they only need an initial voltage of a few hundred volts. This means that electrolytic capacitors can be used with the advantages of a higher lifetime and a relatively higher energy density at lower voltage and smaller weight.
Another advantage of the circuit is that there is no pre-current flowing through the load before the resonant current is activated. Normally, th is is the case because of the resistive division of the current between the opening switch and the load, causing heating of the load. In the resonant series counterpulse circuit, the thyristors prevent this.
The units have been designed to generate currents up to 50 kA. By placing several units in parallel. hi gher counterpulse currents can be generated. This paper will shortly discuss the ope ration of the resonant series counterpulse circuit and the control electronics and present experimental results of the parallel operation of eight units at a current of 300 kA.