GB888442A - Improvements relating to apparatus for testing the tracking of insulating materials - Google Patents

Abstract

888,442. Determining physical qualities. BRITISH ELECTRICAL & ALLIED INDUSTRIES RESEARCH ASSOCIATION. Jan. 25, 1960 [Jan. 23, 1959], No. 2587/59. Class 37. In an arrangement for determining the tendency to form permanent conducting tracks across the surface of an insulating material 2, Fig. 1, due to currents flowing thereover when it is electrically stressed, a predetermined voltage is applied over transformers 50, 40, Fig. 2, to electrodes 1a, 1b which are set to a prescribed distance 4 mm. apart on the insulation, and drops of electrolyte, e.g. ammonium chloride are dropped on to the insulation from a tube 15, the number of drops necessary to give rise to a prescribed current being counted. The drops are released at 30 second intervals by the action of a clutch 25 in the shaft of a motor-driven cam 21, Fig. 4, the cam depressing the plunger stem 19 of a pump 18. The motor 36 which drives the cam also drives a counter 27. A relay D in the anode of a cold cathode triode 77, or a relay C in the anode of cold cathode triode 90, respond respectively to the current across the electrodes, or the table potential when the insulation is punctured to shut down the test, light lamps 80 or 95 respectively, and sound buzzer 81. The test is set up through the successive steps of a selector switch X, the steps being: (1) off; (2) the motor is energized for the drop size to be adjusted by a micrometer adjustment of the plunger stem back stop; (3) the motor is stopped for the test-piece to be placed on the table; (4) Switch X1 is closed to set up a circuit for the manual actuation of self-locking relay B, and the test voltage applied to the electrodes by the actuation of push-button 62 is adjusted at the autotransformer 50; (5) relay A is operated to short-circuit the test gap, and the short-circuit current is set to a maximum value by the adjustment of resistor 42; (6) resistors Y1-Y5 and Z1-Z10 are adjusted to set the current value at which a relay D trips, and its time delay; (7) the material is inserted and the test carried out. Tests are repeated, using different voltages, and graphs are plotted. Suitable shapes of drippipe are discussed and physical details of the test bed. Specification 888,443 is referred to.