GB1004594A - Improvements in and relating to electrical transformers and the operation thereof - Google Patents

Abstract

1,004,594. Transformers. JOHNSON, MATTHEY & CO. Ltd. Jan. 10, 1964 [Feb. 25, 1963], No. 7434/63. Heading H1T. Auxiliary windings 7 (Fig. 1) of an electric transformer A which comprises primary and secondary windings 3, 5 mounted on the central limb of a magnetic core 1, are provided on outer limbs 2 of the core and are connected in series opposition and in such a way across a switch 4 that, on restoring direct A.C. supply to the primary by closing switch 4, sufficient flux change occurs in the central limb, due to the arrangement of the auxiliary windings, to produce a back e.m.f. which reduces the surge current in the primary when the direct supply is interrupted at 4, A.C. will be supplied to the auxiliary windings in series with the primary. Since the auxiliary windings are wound in opposition to produce equal and opposite magnetic effects in the central limb, magnetization of the central limb only occurs due to the reduced current flowing in the primary. At the instant when the switch 4 is closed to shortcircuit the auxiliary windings the increased flow of current in the primary will increase the magnetization in the central limb and this magnetization will bo in the same direction as that provided by one of the auxiliary windings and in the opposite direction to that provided by the other auxiliary winding. A substantial flux change in one half of the central limb is therefore obtained and thus a back e.m.f. which will reduce surge current in the primary will be produced. The central limb may be divided into two portions 1a, 1b (Fig. 2, not shown) on both of which the primary and secondary windings are mounted. The arrangement may be applied to multi-phase transformers.