Recently, digital transformation is being promoted toward the establishment of next-generation power networks 1 2 , and in order to this achieve, it is necessary to collect analysis data under a wide variety of conditions. Circuit breakers are also required to be developed for the overall optimal solution of the power system 3 using monitoring and control technology, and it is expected that the efficiency of operations will be improved with the introduction of DX. The objective is to realize an air circuit breaker that suppresses switching surge voltage when shutting off, determines the opening speed according to the situation, and reduces the size and cost. Focusing on air circuit breakers, it is important to understand the basic characteristics of the arc generated between the electrode contacts in order to achieve miniaturization and high performance. However, few simulation analyzes of the opening speed of the air circuit breaker have been reported. In this research, the arc temperature distribution affected by the opening speed of the air circuit breaker was calculated using the 3-D electromagnetic thermal fluid simulation 4 . Specifically, a non-stationary analysis in which the movable contacts move diagonally over time is calculated.