The design of a 245kV vacuum circuit breaker

Abstract

This paper covers work carried out on the electrical design for a 245kV Vacuum Circuit Breaker, specifically the design of the Vacuum Interrupters. The design is based on a “T” style transmission breaker, with two Vacuum Interrupters in series. The VCB uses a single permanent magnetic actuator with a toggle mechanism to provide the opening and closing forces required and the synchronization of the two Vacuum Interrupters. Vacuum Interrupters are not presently used at these high voltages, but the continuing search for a replacement for the present SF6 based technology for environmental reasons leads us to consider the use of Vacuum Interrupters at ever increasing system voltages. At present single interrupter VCB are in service up to 145kV, and have been for many years. This logically leads to the simple concept of a two break VCB for 245kV Multiple break circuit breakers using both SF 6 and Vacuum technology have been used for many years, and are well proven in service. Rather than taking existing 145kV Vacuum Interrupters and designing a VCB around them, we have taken the approach of designing special interrupters which are intended to work in pairs. Using Vacuum Interrupters in pairs gives significant advantages over single Vacuum Interrupters for these high voltages and this allows us to optimize the vacuum interrupter design for this application. The paper discusses the problems of achieving these high ratings and the methods of optimizing the performance, size, and cost to achieve these requirements. As part of the design process we have modelled the single Vacuum Interrupters and the pair of Vacuum Interrupters using 2D and 3D electrostatic finite element modelling to optimize the voltage design of the Vacuum Interrupters as well as modelling the arc control using 3D electromagnetic finite element modelling to give the required interruption performance. The electrostatic design of the Vacuum Interrupters is discussed in this paper, as well as the design of the VCB. The electromagnetic modelling will be discussed in a future paper.