PROTECTIVE DEVICE FOR VACUUM SWITCH TYPE ON-LOAD TAP CHANGER

PURPOSE:To continue the operation of a transformer by connecting in parallel current limiting resistors and current transformers to the tap-side one of each two vacuum switches connected in series to each of the two taps of a tap winding and detecting an abnormal tap from the output signal of an AC device, and then, returning the abnormal tap to the state before starting operations when the abnormal tap is detected. CONSTITUTION:Main contact valves V1 and V3 and V2 and V4, each of which is composed of two vacuum switches, are connected in series to the taps I and II of a tap winding 1 and the valves V3 and V4 are conneced to the neutral point 9 of a transformer. In addition, serial circuits respectively composed of current-limiting resistors R1 and CT1 and R2 and CT2 are connected in parallel with the valves V1 and V3. The switching operation starting time and completing time of the valves V1 and V2 are inputted to an abnormality detector 15 together with the outputs of the resistors CT1 and CT2. When the detector 15 detects an abnormal tap from the inputted data, the detector 15 displays 16 the abnormal tap and returns the abnormal tap to the state before starting the operations by driving a motor 14 through a control board 13. Therefore, the operation of th transformer is continued.