Determination of Discharge Coefficients for Valves of High Voltage Circuit Breakers

Nowadays, high voltage circuit breaker (CB) simulations are mostly based on Computational Fluid Dynamics (CFD) models. Such simulations require significant computer resources. An alternative approach is to use enthalpy flow models, which do not use space discretization of the interrupter unit chambers and valves. Gas flow is calculated based on state of gas in adjacent chambers and valve settings. However, the valve shape has significant influence on the effective flow cross section between chambers. Therefore, in order to ensure correct simulation results, it is necessary to determine the correct values of discharge coefficients for all valves in the interrupter unit of a circuit breaker. In this paper, the discharge coefficients were determined by combining a series of CFD and enthalpy flow simulations for each valve in the interrupter unit. After that, discharge coefficients are used as input for further simulations based on the enthalpy flow model. This way, benefits from both models are combined: more precise gas flow calculation and faster simulations. The proposed novel approach is validated in a high-power laboratory by pressure measurements on a 420 kV 63 kA self-blast circuit breaker.