GB262553A - Improvements in or relating to control systems for electrical apparatus such as motors - Google Patents

Abstract

262,553. Scarf, C. T., Last, C. H., and Metropolitan-Vickers Electrical Co., Ltd. Oct. 16, 1925. Protective arrangements.-In a control system for electric motors, particularly coal-cutting machines 36, wherein the reversing control switch 24 - - 26 at the machine end is relieved of the making and breaking of power currents by the remotely-disposed circuit interrupter 11 - - 13 at the gate end, the control of the interrupter is effected by circuits which include one of the power conductors 3 jointly with a pilot conductor 48, 49 of the five-core trailing cable, so that the complete continuity of these conductors is necessary before the motor can be energized. A closing relay with operating coil 47 and contacts 83, 52 controls the energization (from phases 1 and 2 of the supply) of the closing coil 50 of the interrupter. Its coil 47 is connected in series with the secondary 46 of a low-voltage transformer (the primary of which is connected across phases 1 and 2), the contacts of a master relay having a winding 77 and contacts 80, 82, the pilot conductor 48, 49, contact 28 of a pilot switch 28, 72 interconnected with the motor control switch and through the switch 28 to the earthed conductor 42, 41 of the cable. Thus the closing relay cannot be operated to effect the closure of the interrupter until the contacts 80 of the master relay and 28 and 38 or 39 of the pilot switch have been closed. The portion 72, 71 of the pilot switch has a lost-motion connection with the operating handle which closes the control switches and the two parts of the pilot switch in a predetermined order, as shown. The operating coil 77 of the master relay is connected in series with the low-voltage secondary 46, the power conductor 3 (on the side of the interrupter remote from the supply), the contact-member 72 of the pilot switch and so to earth when the member 72 engages with its fixed contact 71. To close the interrupter it is therefore necessary that the circuit of the master relay be closed in order that the circuit of the closing relay may be closed. Since an arc may persist at the contacts of the interrupter for a time on opening, an arcing relay 91 with an overload coil in the phase 3 is mechancally interlocked with the interrupter so that, when the interrupter opens, the control circuit which includes the master relay, closing relay, &c. is connected to the phase 3 only after the arc has subsided and line 3 is dead. The supply circuit to the primary of the low-voltage transformer includes a leakage protection relay 7 carrying the summation current induced in the secondary 6 of a transformer 5 with three primaries in the phases and an overload transformer 56 energized by two of the phases. The earth connection of the secondary of the transformer has in it a mercury tilting switch 76 so that if the apparatus is appreciably tilted the interrupter circuit is broken to ensure safety.