A novel on-line calibration method for CVT

Time-consuming, hard to getting real-time data errors and complex wiring are the notable defects of CVT (Capacitor Voltage Transformer) off-line calibration. In order to solve such problems, based on calibration mechanism of CVT and working performance of the LVQB CT (Inversion SF
₆
Gas-insulated Current Transformer, which is a naming method of Chinese manufacturer), a novel on-line calibration method for CVT is presented. This method converts the LVQB CT into the standard capacitor to finish the on-line calibration. The corresponding specific modification scheme is also proposed by the authors. To ensure the feasibility of the method, the dielectric properties of LVQB CT under different working mode (measure mode and calibration mode) are analyzed. A FEM field simulation model is established and the electric field strength is calculated. The simulation results reveal that both measurement mode and calibration mode meet the insulation requirements. However, if we focus on the working mode switching process, it is not hard to find that a very high floating potential will occur under the condition of the change-over switch interlocking. Once this happens, the gap between the insulation pad and the shielding cover of LVQB CT will be breakdown, which may threaten the calibration system of CVT. For this reason, measures must be taken to improve the insulation performance of the calibration system.