Influence of a Short-Duration Arc on the Erosion and Dielectric Strength of Narrow Air-Gap Contacts in a Hybrid DC Switch

Contact erosion and dielectric strength reduction due to arc discharge are critical problems, particularly for dc switches and circuit breakers. Long-duration arcs not only cause serious contact erosion but also reduce the dielectric strength of the contact gap. A hybrid dc switch composed of a mechanical switch (MS) and a semiconductor device can drastically decrease the duration of the arc compared to a conventional MS. This paper aims to examine the influence of short-duration arcs on the contact erosion and dielectric strength in a hybrid dc switch. A dc current of up to 800 A is flown through copper contacts that are connected in parallel with a SiC-MOSFET. An arc discharge is formed between the contacts just after they are opened. Then, a pulsed high voltage is applied between the contacts to measure the breakdown strength of the contacts. A piezo actuator opens the contacts, which have a gap length of 300 μm. When the dc current is increased from 200 to 800 A, the arc duration increases from 4 to 14 μs and causes surface erosion and lengthened protrusions. The contact resistance does not increase. However, the breakdown electric field is decreased.