GB499817A - Protective system for high voltage transformers and the like - Google Patents

Abstract

499,817. Protective cut-out arrangements. BRITISH THOMSON - HOUSTON CO., Ltd., KINMAN, T. H., and HIBBERD, R. G. July 26, 1937, No. 20640. [Class 38 (v)] A protective arrangement for a transformer comprises a pick-up coil or equivalent device made to resonate at one of the high frequency resonant peaks of the transformer and / or circuit associated therewith, and arranged within the transformer tank so as to be capable of receiving energy at the frequency to which it is resonant while being shielded so as to be unresponsive to extraneous energy of that frequency, amplifying means for the energy induced in the coil, and a protective device operated from the output of the amplifying means. The high-frequency resonant peaks are due to inherent inductive reactance and capacity of the transformer windings or winding sections. The pick-up coil may be replaced by a short rod or wire insulated at one end and connected at the other end through a limiting resistance R to the grid of the amplifying valve T, which may be of the type known under the Registered Trade Mark " Thyratron.'' Anode and grid of the valve arc connected to opposite ends of supply transformer M so as to be supplied with potentials of opposing phase, the grid being adjustably biassed by a slider resistance S so that normally no ionization occurs. The pick-up coil is coupled through condenser G<1>, and an inductance L arranged in the grid circuit has the maximum voltagedrop produced across it over a band of high frequencies corresponding to certain resonant peaks, an arrangement which allows for application to transformers of different types. A relay coil or indicator O is provided in the output-circuit. By enclosing the pick-up coil in the tank or in a screening box in the tank, extraneous pick-up is prevented. A tuned radio-frequency circuit may be formed by winding one or more of the leads connecting the H.T. secondary windings with the terminals in the form of a helix, and this may be coupled to a circuit comprising' a single loop of wire connected across condenserterminals which are also connected to a relay and valve preferably arranged in a screened box outside the tank, the valve being a highvacuum one. Brush discharge in either terminal or winding end sets up oscillations in the tuned circuit of a frequency determined by the inductance and capacity. Specification 336,184, [Class 38 (iv)], is referred to.