It is shown that

with the current understanding of basic arc physics

CAD tools based on a mathematical model encompassing all important physical processes can be developed to aid the design of autoexpansion circuit breakers. The model takes account of radiation transport

arc radiation induced inner wall ablation

turbulence enhanced momentum and energy transport

and the moving parts of the breaker. With the aid of the PC based PHOENICS

a commercial general purpose computational fluid dynamics （CFD） package

the conservation equations for the gas and arc together with the relevant Maxwell’s equations can be solved. The temperature

velocity and electric fields within the breaker can easily be visualised and the thermal interruption capability predicted. The effects of changing design parameters can be simulated in detail

thus reducing the number of short-circuit tests. Results are verified by available tests.