Test Setup Design for Measuring the Conductance in the Mechanical Part of Hybrid-Circuit-Breakers Before and After Current Commutation

Abstract

The number of devices either providing or demanding direct current is growing more and more. This led to the renascence of DC grids and revealed a need for research. One critical component is the DC circuit breaker. It has to handle nominal and fault currents to keep the grid stable and operable. Interrupting currents in DC grids can be challenging because of the absence of a natural current zero crossing. Therefore, complex arcing chambers are needed. Especially at low currents, the self-induced force may not be sufficient to force the arc into the arcing chamber. Hybrid circuit breakers (HCB) are one possible solution to meet theses sophisticated requirements. There are several different topologies. All have in common that mechanical switches and semiconductors are combined to create a switch with the advantages of both technologies. One simple solution consists of two mechanical switches and one bypassing semiconductor circuit. The arc is used to achieve commutation from the mechanical to the semiconductor branch. While it carries the current, the mechanical switch regains its dielectric strength. Since this recovery time is short, the semiconductor can be overloaded within the limits of its thermal capacity. Defining the recovery time can be challenging. In addition, the effect of contact distance, arcing time and current value are unknown. To research the recovery behavior a model-switching chamber with an adjustable contact gap is developed. This device under test (DUT) was implemented into a test circuit that reproduces part of the hybrid switching process. When the arc between the contacts of the DUT reaches its steady state, a parallel commutating path is activated. The residual conductance of the decaying arc was measured. The development and several iteration steps of the test circuit and DUT are laid out. Finally, some test runs and initial measurements are presented.

Keywords

• Arc conductivity
• dielectric recovery
• direct current
• hybrid DC circuit breaker
• recovery behavior
• test circuit development