ARRESTER AND METHOD FOR DETECTING ITS DETERIORATION

PURPOSE:To detect the deterioration of an arrester while the arrester is connected to an AC-DC transformer by measuring a leakage current by connecting a leakage current measurement circuit to the low-voltage side of the arrester and controlling the firing angle of a thyristor valve to a fixed value. CONSTITUTION:A leakage current detection circuit 9 is connected to the low- voltage side of a valve protective arrester 7. The circuit 9 is constituted in the form of a ladder type circuit in which a circuit composed of a protective element formed by connecting in parallel a zinc oxide varistor 10, capacitor 11, and Zener diode 12 and connecting the high-voltage sides of the capacitor 11 and diode 12 to each other through a resistor 13 is connected in parallel with an ammeter 14. The varistor 10, capacitor 11, diode 12, and resistor 13 constituting the protective element of the circuit 9 protect the high-sensitivity ammeter 14 from high voltages and large currents. Therefore, it is desirable to not always energize the circuit 9, but at the measuring time only, and, when a switch 15 is provided, the occurrence of erroneous measurement caused by a fault of the ammeter 14 can be prevented.