Arc control systems for AMF high voltage vacuum interrupters - modeling the contact gap

At present there is a clear trend for vacuum circuit breakers to move up in voltage class from distribution voltages to transmission and sub-transmission voltages. Developing new vacuum interrupters for these voltages poses a number of challenges, not least the requirement to interrupt large short circuit currents at high voltages. This requires the development of new arc control systems which are effective at the large contact gaps necessary for these high voltages and also have relatively low resistance when closed. The paper forms part of a study examining the design challenges in extending the operation of existing geometries to higher voltages suitable for the larger contact gaps necessary for systems up to 245kV, and in particular investigates the effect of large contact gaps on the magnetic field which is used to control the arc. This paper concentrates on the Axial Magnetic Field (AMF) type of arc control systems. The alternative Radial Magnetic Field (RMF) type of arc control for this application will be the subject of a future paper.