Engineering Evaluation Method for the Breaking Capacity of Circuit Breakers under Excessive DC Component of Short-circuit Current

Both the AC and DC components of short-circuit current can affect the breaking capacity of a circuit breaker. This article analyzes several methods for checking the breaking capacity of circuit breakers under the condition that the AC component of short-circuit current in substations does not exceed the standard but the DC component exceeds the standard. The most rigorous engineering verification method, the rectangular cumulative charge equivalent method based on type test data, is determined as the preliminary evaluation of the breaking capacity of circuit breakers. For circuit breakers that fail verification, considering their mechanical characteristics and the structure of the arc extinguishing chamber, a refined verification and structural optimization based on magnetic fluid dynamics arc simulation is adopted. The method proposed in this article is highly practical, especially suitable for scenarios where a large number of different types of switches have excessive DC components in large power grids. It can effectively improve the efficiency of verification calculations and ensure the safe and stable operation of the equipment.