Patent GB-405614-A (GB)
Title: Improvements in and relating to protective arrangements for electric apparatus
IPC: H02H3/14
Filed: 1932-07-27
Abstract: 405,614. Protective cut-out arrangements. INTERNATIONAL GENERAL ELECTRIC CO., Inc., 120, Broadway, New York, U.S.A.-(Assignees of Allgemeine Elektricitats-Ges. ; 2, Friedrich Karl-Ufer, Berlin.) July 27, 1932, No. 21248. Convention date, July 27, 1931. [Class 38 (v).] In a protective arrangement for electrical apparatus of the type in which an indication or cut-out operation is controlled in accordance with the insulation-resistance of the leakage path, a normally dead portion of the apparatus is connected in the control circuit of an electric discharge device the anode circuit of the device being, at least when the apparatus is functioning, connected to the supply source through the control coil of a switching device, the arrangement being such that when a change of voltage occurs in the control circuit owing to the increase of potential of the normally dead part above a predetermined value, an anode current commences to flow whereby the switch is operated to disconnect the faulty apparatus. As shown in Fig. 1 a lamp 37 on a meter board has a normally dead part, that is, the lamp holder 5, connected to the grid of a discharge tube 6. The grid normally has a bias provided by a battery 17 so that practically no anode current flows from the live main 3, through the operating winding 10 of the circuitbreaker 12-16. If however, the insulation resistance of the holder 5 becomes impaired the rise in potential across a high resistance 19 connected between the grid and the earthed main 4 causes an increase of the grid potential which causes anode current to flow. When a sufficient anode current passes through the circuit-breaker operating coil 10 the circuitbreaker is opened and the lamp and other apparatus automatically disconnected, the circuit-breaker being latched automatically in the open position. In a modified arrangement (Figs. 3 and 4, not shown) applied to a water heater two discharge devices are employed and are arranged so that when the tank becomes charged above a predetermined potential due to leakage from one or other of the supply mains the supply current is automatically cut off. In a further modified arrangement shown in Fig. 5 for use in a cattle shed the grid 53 of the discharge device 50 is connected to a member 46 of the metal work of the building the cathode 51 being earthed and the anode 52 being connected to a main 44 through a relay coil 54. When a sufficient voltage appears at the grid the supply circuit is cut off by the anode current of the discharge device causing the opening of switch 55 in the circuit of the circuit-breaker maintaining coil 47. In a similar modification (Fig. 6, not shown) rise in voltage on a machine casing is similarly prevented. The anode current may, alternatively, be derived from the supply side of the controlled circuit-breaker. Any form of grid-controlled electronic discharge device may be employed although it is preferable to employ a grid-controlled glow tube or grid-controlled arc discharge device with gas or vapour filling and hot cathode. In such arrangements the discharge devices could be employed to act also as excess voltage relays.