GB524862A - Improvements in or relating to the testing of electrical insulators - Google Patents

Abstract

524,862. Detecting faults. BUSHING CO., Ltd., and BROWN, W. J. Jan. 13. 1939. No. 1185. [Class 37] An insulator of a power conductor is tested by coupling to the live conductor an indicating apparatus tuned to a frequency of the order of 1500 kilocycles per second and serving to detect a high-frequency disturbance superimposed on the normal current wave, thereby indicating the presence of ionization. The indicating apparatus shown comprises a highfrequency input transformer A1, A2, a valve detector E, and an amplifier K. The primary winding A1 of the input transformer is connected across a search coil B placed in the field of the main conductor. Alternatively this winding may be connected across the secondary winding of a current transformer or in the earth lead of an ionization-free condenser. The secondary winding A2 is connected through a grid leak C and condenser D between the grid of the detector valve E and earth F. Across the secondary winding A2 is a tuning condenser G, and between the anode of the detector valve E and earth are a reaction coil H and a variable condenser J. The amplifying valve K is coupled to the detector valve E by a transformer L and includes in its anode circuit an indicating device such as a telephone P, a cathode ray oscillograph, or an ammeter. The indicating apparatus is tuned to a frequency of the order of 1500 kilocycles per second, a disturbance on the main current wave being detected as a buzz in the telephone, a deflection on the ammeter, or a disturbance on the wave form in an oscillograph. If a current of the same frequency as the main current but in opposite phase is injected the main current wave in the oscillograph is neutralized and only the image of the disturbance appears.