GB635902A - Improvements in and relating to protective apparatus for polyphase electric systems - Google Patents

Abstract

635,902. Protective cut-out arrangements. BRITISH THOMSON-HOUSTON CO., Ltd. Oct. 16, 1946, No. 30841. Convention date, Oct. 16, 1945. [Class 38 (v)] In the protective arrangement of Specification 560,429, the impedance-shorting switch described in Specification 176,191, [Class 38 (v)], is arranged to be reopened a predetermined number of times at set intervals on the occurrence of an open-phase conductor. When the byepass switch 14 is closed on fault, a timer-motor 41 is energized over contacts 60 and timer-contacts 56, 49, 54, 48. A cam 43 quickly permits the contact 48 to engage a contact 53 so that the motor is now energized over normally-closed contacts 69 of a relay 68, and the contacts 53, 48. A parallel circuit is also completed through normally-closed contacts 66 of a relay 63, provided that there is insufficient current through the switch 14 to energize the relay coil 64, such as would be the case if a ground fault had been cleared by the impedance 13, or if there was an open-phase conductor. Shortly afterwards, a contact 47 is moved by a cam 42 with three raised portions to engage a contact 52 and energize an auxiliary relay 59 over contacts 50, 57 and 60. The cam 42 rotates still further so that contact 47 re-engages contact 51 to energize the relay 68 over contacts 61 of the relay 59, contacts 51, 47, locking contact 62, contacts 57, 50 and 60. Contacts 69 thus open and if the fault is a ground fault, coil 64 will be energized and contacts 66 open also, de-energizing the motor 41. If the fault is an open-phase, contacts 66 will be closed and the motor will continue to run. The contacts 67 of relay 63 are closed and a relay 36 is energized over contacts 39, 67, 61, 51, 47, 62, 57, 50 and 60, to energize a winding 34 and open the switch 14. The contacts 39, 60 are therefore opened and relays 36, 59 de-energized, the latter de-energizing the relay 68. The motor 41, however, still runs, since the contacts 53, 48 are still closed. If the open-phase fault still persists, the switch 14 is again closed, and the second raised portion of the cam 42 causes the relays 59 and 36 to begin a second cycle to reopen the switch. This continues for the predetermined number of times, whereupon the switch 14 remains closed, since a cam 45 causes the contact 50 to engage the contact 58 to break the circuit of the coil 36 and also sound an alarm 71. The motor 41 also is cut out by the opening of contacts 48, 53. With a sustained ground fault, the switch 14 closes and remains closed since the coil 64 is energized, so breaking the circuit of the motor 41 at contact 66. As soon as the fault is cleared, the motor 41 restarts and the switch is opened. The Specification as open to inspection under Sect. 91 refers also to U.S.A. Specification 1,537,371. This subject-matter does not appear in the Specification as accepted.