Patent GB-964315-A (GB)
Title: Improvements relating to electrical transformers
IPC: G05F3/06
Filed: 1959-11-14
Abstract: 964,315. Transformers. D. KARO. Nov. 14, 1960 [Nov. 14, 1959; Feb. 2, 1960; Feb. 25, 1960; March 24, 1960], Nos. 38669/59, 3604/60, 6566/60 and 10411/60. Heading H1T. A constant voltage transformer has primary coils P 1  and P 2  (Fig. 3), arranged on a main limb 10a, 10b on opposite sides of a saturable shunt member 15, the secondary 5 being arranged with all or part of its windings nearer to shunt 15 than coil P 1 , shunt 15 being fully or partly saturated during normal operation and P 1  and P 2  being arranged to assist one another in setting up magnetic flux in shunt 15. The main limb is unsaturated or is less saturated than shunt 15. A capacitor C may be incorporated and connected in series with P 1  and in parallel with P 2 , the reactance of C being greater than that of P 2  so that the combined reactance of the two is capacitative. The use of capacitor C in series with P 1 , which together operate on a part of the primary current/voltage curve 5 (Fig. 7), beyond the resonance point 5b, enables sufficient values of current I 1  and I 2  to be established in windings P 1  and P 2  to produce the desired saturated condition in shunt 15. Curve 6 illustrates the variation of secondary voltage with I 1 . If waveform and efficiency are not important C can be dispensed with, P 2  being wound in the opposite direction. The device can be arranged, e.g. to suppress or minimize a selected harmonic caused by saturation, or to maintain the secondary voltage constant despite considerable increases in the primary voltage, by suitably proportioning the effects of the m.m.f's produced by P 1  and P 2 . Fig. 6 (curve III), illustrates the effect of adding a suitably arranged coil P 2 . The windings may be movable and/or either or both of the primary coils P 1 , P 2  may be tapped. The depth of the slots 16 in shunt member 15 may be variable and other slots, adjustable in depth and position, may be provided in the lower edge. The laminations are held in buffing position by screwpressed pressure bars, shims being provided if desired. In an alternative arrangement (Fig. 8) capacitor C is connected in parallel with P 1 , the combination operating normally beyond resonance point 5b (Fig. 9), and P 2  being wound oppositely to P 1 . A smaller capacitor is needed than for the Fig. 3 arrangement and the transformer now operates with a lagging power factor. An auxiliary winding may be connected in series with the capacitor, the two together being connected in parallel with either of the primary coils (Figs. 10 and 11, not shown). In another arrangement phaseshifting windings connected together in series through a variable impedance may be associated with the two primary windings (Fig. 12, not shown). Alternatively, an auxiliary secondary winding may be provided (Fig. 13, not shown). According to the first Provisional Specification, the upper part of the main limb may be wholly saturated. According to the second Provisional Specification, the secondary may be divided into two or more portions, one of which is movable. According to the fourth Provisional Specification, there may be more than three primary coils and the windings need not be on the main centre limb.