Model-based Optimization of the Switching Performance of a Switch Disconnector

Abstract

Low voltage switch disconnectors (SD) combine rated load switching with disconnector functionality, providing safe electrical isolation. Electrical contacts are separated forming an arc discharge that needs to be quenched at first current zero (CZ) to protect the load and the SD itself. With increased line voltage, interruption at first CZ crossing is getting more difficult due to increased transient recovery voltage (TRV) and larger post arc current, leading to excessive contact erosion with longer arcing time. Arc simulation methodology was utilized to improve the design for better arc cooling close to CZ. Therefore, benchmark values of arc resistance and thermal time constant were evaluated close to CZ for a successful test at lower line voltage. The cooling efficiency of different designs at higher line voltage was analyzed by 3D arc simulation. A revised design was able to clear overload currents at lower and higher line voltages at first CZ, preventing excessive contact damage.