GB735371A - Improvements in and relating to electrical transformers having on-load tap changing apparatus - Google Patents

Abstract

735,371. Transformers. ENGLISH ELECTRIC CO., Ltd. Jan. 15, 1954 [Jan. 16, 1953], No. 1331/53. Class 38 (2). A transformer tap changing system comprises a transformer 20, having two secondary windings 20b, 20c each provided with a set of corresponding tappings and drum-type tap changing gear 33 which operates in a sequence which includes the following steps: (a) connecting an inductor 34 between a tapping 25 on secondary winding 20c and a corresponding tapping 29 on secondary winding 20b; (b) connecting the tapping 25 on the secondary wind-. ing 20c to a further tapping 30 on the secondary winding 20b and the tapping 29 on the secondary winding 20b to a further tapping 26 on the secondary winding 20c and (c) disconnecting the connections between the inductor 34 and the tappings 25, 29 on the secondary windings 20b, 20c. The inductor 34 has a mid-tap forming a common output connection to a load 24 which may be a D.C. load fed through rectifiers 22, 23. The mid-tap also allows the inductor to be short circuited after a connection has been made during a tap change operation, this short circuit being removed however before the disconnection step is made. If, however, the regulation of the equipment is not critical this short circuiting may be omitted. The leakage reactance of the inductor may be made to have a high value to exert a smoothing effect on the system.