GB623539A - Systems for indicating the effective age of electrical apparatus - Google Patents

Abstract

623,539. Electric meters. BRITISH THOMSON-HOUSTON CO., Ltd. March 1, 1945, No. 5081. Convention date, March 1, 1944. [Class 37] [Also in Groups XIX, XXXV and XXXVIII] To obtain an indication of the true or effective age of electrical apparatus which ages more rapidly when operated above a certain temperature, a recording and indicating instrument is used which is operated from the apparatus and controlled by a thermallyresponsive device connected to. the apparatus. As applied to a transformer 7, the age-indicating means comprises a motor 10, operated from the transformer, driving through speed-reduction mechanism 12 a disc 13 which rotates a disc 14 frictionally through a magnetic ball 15 to drive, through further speed-reduction mechanism 18, a counter 19. The arrangement is such that the counter shows the physical age of the apparatus in equivalent years of service. The position of the ball 15, which controls the speed ratio between discs 13, 14, is controlled by a bimetallic thermostat 16 located in the oil &c. in the transformer tank 8, so that the counter registers faster when the temperature of the transformer increases. In a modification, the ball 15 itself is driven by the motor 10 to rotate the disc 14, and the position of the ball is controlled by a cam face movable by levers controlled from a thermalresponsive device comprising a metallic bellows, a capillary tube and a bulb which contains a liquid and is heated by a resistance coil to the temperature of the transformer. An indication of the rate at which the apparatus is ageing is given by a device 22 of the speedometer type. The whole arrangement may be replaced by a kilowatt-hour meter 51, Fig. 5, having the voltage terminals 52 connected to the transformer, and the current terminals 53 in series with a small transformer 55 in the transformer circuit and a resistance 56. The resistance 56 is such that its resistance diminishes with increase in temperature, and it is heated by a coil 31 to the temperature of the transformer. The scale markings of the meter are graduated in years and fractions thereof. In a modification of Fig. 5, the current-leads of a reactive kilovolt-ampere-hour meter are in series with an inductance coil having a magnetic core of such a nature that permeability rapidly decreases with increasing temperature, such as an alloy consisting of 68 per cent iron and 32 per cent nickel.