GB619484A - Improvements in and relating to load-ratio-control circuits for transformers - Google Patents

Abstract

619,484. Transformers. BRITISH THOMSON-HOUSTON CO., Ltd. Dec. 12, 1946, No. 36754. Convention date, Dec. 12, 1945. [Class 38 (ii)] In an on-load tap-changing system for a transformer, in which, when two taps 3, 4 are connected in circuit together the value of the circulating current is restricted by an impedance 8, the effective value of the impedance 8 is reduced when an arcing contactor 11 or 12 is opened to disconnect one tapping from the circuit. When moving contacts 9, 10 engage separate taps 3, 4, half the load current flows through each of the inductively coupled halves of the centre-tapped inductor 8. Prior to moving contact 9, an arcing contactor 11 is opened to break current in this branch. Under shortcircuit load conditions, the heavy current through the left-hand half of inductor 8 which acts as an auto-transformer, induces a restricting voltage which maintains the arc. When contact 15 is engaged, an inductor 14 is connected in parallel with the inductor 8 with respect to the current in the arc so that the effective inductance and therefore the restricting volts are reduced and the arc goes out. The effective inductance is still sufficient to restrict the circulating current. Contactor 12 operates similarly before contact 10 is moved from tap 4. In a modification each half of the inductor restricting the circulating current is divided into two parts, one of which is short-circuited in the full open position of the arcing contacts, Fig. 2 (not shown).