GB375024A - Improvements in arrangements for the automatic protection of electric circuits - Google Patents

Abstract

375,024. Protective cut-out arrangements. MACINTOSH CABLE CO., Ltd. and FROST, J. T., Sinfin Lane, Normanton, Derby. May 4, 1931, No. 13098. [Class 38 (v).] In the protection of apparatus comprising an automatic circuit-breaker 30 at the near end connecting through a cable such as a trailing cable to consuming apparatus such as a coalcutter at the far end, the circuit-breaker is closed and maintained closed by a coil 33 deriving its energy through a pilot wire from the small transformer 34, 37 at the switch end and when once closed the maintaining circuit is changed over to a supply from the transformer 43, 40 at the consuming end. The trailing cable, in addition to the three supply conductors, has a pilot wire 6 which is connected through the cable couplings on the one side through the actuating and maintaining coil 33 and the secondary winding 34 of the transformer to the earthed casing of the switch and on the other side through the secondary 40 of the second transformer the primary of which is connected across two of the phases of the motor. When the breaker 30 is open the auxiliary contacts 31 are closed and the transformer 34, 37 is energized to supply the coil 33 if the earthed pilot cable is sound. The breaker is thus closed, the maintaining circuit broken at 31 and a new maintaining circuit established at the line transformer 43, 40. If the trailing cable becomes disconnected the pilot wire broken or earthed to the earth conductor 7, the supply to the coil 33 is discontinued or reduced so that the breaker opens.