Capacitance simulation method for HV-VCB with floating potential shield design based on FEM

Summary

Various high-voltage apparatus, such as high-voltage dividers or high-voltage switchgear, divide the applied voltage over series components. One single component would be insufficient to withstand the stress of a full voltage load, so a series of components are connected as one high-voltage apparatus. This means the voltage must be symmetrically distributed over the whole installation. For asymmetric capacitances, the voltage distribution is also asymmetrical and can cause a flashover. Significant efforts in design are made to avoid a breakdown, which requires the exact field distribution and capacitance to be known. A solution to this is using finite element method (FEM) simulation programs, which offer the advantage of simulation results in good approximation. The simulated potential and electric field distribution inside the highvoltage apparatus helps to prevent failures such as particle breakdown in long gaps and field emission in short gaps. For a well-matched high-voltage apparatus, it is also necessary to know all inside capacities, including the capacitances to components on floating potentials. In this study, a simple shield design for a vacuum circuit breaker (VCB) was simulated with COMSOL to determine the partial capacitances of the installation. In this way, the charges on floating components were derived to calculate the capacitance in consideration of the electrical field and the respective potential. To verify the methodology, a simple model in 2D was used to simulate all necessary values and to calculate the capacitance. The simulation results helped improve the shield design and thus the switching performance of the high-voltage VCB. The methodology in this study enables the calculation of partial capacitances of complex geometries in COMSOL. It is also possible to transfer the methodology to several other high-voltage applications with capacitive coupling mechanisms.

Additional informations

Authors

HILBERT, KURRAT, PYKALA

Keywords

vacuum circuit breaker, vacuum interrupter, switching in vacuum, electric field simulation