GB388110A - Improvements in protective gear for alternating current electrical machinery - Google Patents

Abstract

388,110. Protective cut-out arrangements. HILL, E. P., 37, Radstock Road, Stretford, Manchester, and ASSOCIATED ELECTRICAL INDUSTRIES, Ltd., Crown House, Aldwych, London. Oct. 6, 1931, No. 27778. [Class 38 (v).] Relates to the protection of synchronous machines such as rotary converters 1 and motors against damage to the windings while they are being started up (as asynchronous machines) by the application of an alternating current at low voltage, derived from a tap-changing transformer 3, with the circuit of the D.C. excitation winding 5 closed on itself or through a resistance. According to the invention, a long time-lag protective relay 9, which may be of the induction type, is located in the circuit of the D.C. winding so that, if the starting operation takes an abnormal time, the alternating current which circulates in the winding and attains zero frequency when synchronism is reached, lasts long enough to close the contacts 13 of the relay and trip the main currentbreaker. The invention is shown applied to a synchronous converter, the shunt field winding being connected with the armature winding on the D.C. side through a change-over switch 6, the usual field control resistance 8 and the time-delay relay. The change-over switch enables the polarity of the D.C. side to be reversed if necessary. When synchronism is reached in the normal time, the full voltage is applied by means of the switch 4 and the relay is cut out of circuit by means of the switch 15.