GB367065A - Improvements in or relating to the control and protection of electrical apparatus - Google Patents

Abstract

367,065. Protective cut-out arrangements. BRITISH JEFFREY-DIAMOND, Ltd., Stennard Works, Wakefield, Yorkshire, and TINSLEY, H., 289, Lidgett Lane, Moortown, Leeds. Nov. 29, 1930, No. 36031. [Class 38 (v).]. In the distant control combined with the protection of portable earthed electrical apparatus (such as coal-cutters) by means of a low voltage circuit derived from the mains and having an earth return through the earthed apparatus as in Specification 248,805, [Class 38 (v), Electric switches &c.], a low voltage direct current is used derived from a full-wave non-rotary rectifier 1 connected to the A.C. mains through a transformer 2. The D.C. side of the rectifier is connected on the one hand to the earthed frame 10 of the main gateend switch 4 and on the other, through a closing and maintaining coil 5 of the switch 4, through a pilot trailing cable 6, through a limiting resistance 7 and the starting switch 8 on the motor to the earthed frame of the motor. By closing the switch 8 the energized solenoid 5 raises the main switch to the closed position ; if the earthing circuit fails, so that the apparatus is no longer earthed, the solenoid 5 is deenergized and the main switch assumes the off position. On overload in the main circuit, the overload coils open the switch 14 in the maintaining circuit, or the core-balancing arrangement 11 breaks the circuit of the primary of the transformer 2 with the same result. If the low voltage trailing cable develops a fault to earth, the limiting resistance 13 is no longer in the circuit, the voltage across the solenoid 5 is excessive and, in consequence, an auxiliary solenoid 13 connected across the solenoid 5 becomes energized sufficiently to raise the switch 14 to the open position and break the maintaining circuit. Indicating lamps 15 show that the main switch is closed and that the rectifier is working.