GB743988A - Improvements in and relating to electrical relays - Google Patents

Abstract

743,988. Induction relays; protective cutout systems. ENGLISH ELECTRIC CO., Ltd. Oct. 2, 1953 [Oct. 3, 1952], No. 24843/52. Class 38(5) A transformer protection relay, responsive immediately to faults in the transformer but not responsive to the momentary large inrush of current which occurs when the transformer is switched on comprises an induction disc co-operating with an operating magnet 1 having two pairs of shaded poles a, b and c, d arranged on opposite sides of an unshaded pair of poles e, f; the windings on the poles a, b are in series with a condenser 12 tuned to give maximum torque to the disc in a contactclosing direction at the fundamental frequency of the enegizing current, while the windings on the poles c, d are in series with a condenser 15 tuned to give maximum torque in the opposite direction at the second harmonic of the supply frequency. The relay therefore does not respond to a momentary large inrush current since this contains even harmonic components which influence the restraining action of the poles c, d sufficiently. The induction disc may also be influenced by a restraining electromagnet 2, Fig. 4 and the windings 9 and 16 of the two electromagnets 1, 2 may be connected up in a protective system as shown in Fig. 6. Here the transformer is shown at 20 and current transformers 21. 22 on the input and output circuits convey current to the windings 9 and 16. When a fault occurs within the protected transformer 20, a large current flows in winding 9 to operate the relay but the currents in the two halves of winding 16 oppose each other so that the restraining action of magnet 2 is inappreciable. Specification 743,985 is referred to.