GB634496A - Improvements in transformers having ratio-control means - Google Patents

Abstract

634,496. Transformers. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 8, 1946, No. 33299. Convention date, Nov. 8, 1945. [Class 38 (ii)] One winding of a transformer comprises two equal voltage sections, one end of each being connected together through one winding of an auxiliary transformer, the other ends being connected through the other winding, the terminals for the connections to the winding of the main transformer being connected, one to a fixed tap on -that winding and the other to one or more adjustable contacts which move over taps on the sections. The secondary winding of a transformer 1 is divided into two parts 5, 6, the ends of which are connected to the ends of similar windings 9, 10 of another transformer 8, so that the polarities of secondaries 5, 6 oppose and of windings 9, 10 assist. The connections 4, 4 of the secondaries 5, 6 to the external circuit in supplying which they or parts of them are effectively in parallel, are made respectively to one end of secondary 5, and to contacts 11, 12 which engage tappings on secondaries 5, 6 respectively. During on-load tap changing, contacts 11, 12 are alternately at points at the same and at different voltages. This voltage difference produces circulating currents in two circuits-shown by the dotted and solid arrows respectively-which each include parts of the secondaries 5, 6 equivalent to the whole of one winding, and one of the windings 9, 10, the induction between which keeps the two circulating currents equal.' Whatever the transformation ratio of the main transformer 1, when the contacts 11, 12 are at points of unequal voltage, the two equal circulating currents are unchanged as they flow through similar paths with equal impedances which remain unchanged. A modification is described in which the two secondary windings are wound together with alternating turns along which a sliding contact moves to touch, first a turn of each winding and then a turn of one only, Fig. 1 (not shown). The invention may also be applied to auto-transformers in which the regulation is all bucking or boosting, Fig. 3 (not shown), or includes both bucking and boosting, Fig. 4 (not shown).