Analysis of Breakdown Mechanisms in Heated Short Air Gaps During Contact Opening in Compact DC Circuit Breakers

DC commutative circuit breakers, characterised by their compact size and rapid commutation capabilities, are increasingly recognised for their potential in DC circuit inter-ruption. However, challenges such as arc re-ignition significantly hinder their scalability. This paper reviews traditional predictive models for breakdown behaviours, particularly Paschen's Law and Critical Field Theory, to explore their adequacy in explaining the mechanisms behind re-ignition post-commutation. This research addresses the observed discrepancies between theoretical predictions and experimental results in compact LC commutative circuit breakers, particularly in scenarios involving rapid contact separation and the presence of hot gas in the gap. It proposes that the Critical Field Theory, due to the remaining noticeable background ionisation, more accurately describes the breakdown mechanism during contact opening. The proposed study integrates detailed modelling of temperature distribution, electrical phenomena associated with the arc, and airflow effects within the air gap, supported by experimental validations. The findings enhance our understanding of the electrical breakdown dynamics and provide insights into improving the design and reliability of DC circuit breakers.