Patent GB-751791-A (GB)
Title: Improvements in or relating to electric motor controllers
IPC: H02P7/00
Filed: 1954-03-22
Abstract: 751,791. Magnetic amplifiers. BAILEY METERS & CONTROLS, Ltd. March 22, 1954 [March 23, 1953], No. 8345/54. Class 40 (4). [Also in Group XXXVIII] A magnetic amplifier in an electrical indicating system (see Group XXXVIII) is controlled by an alternating input signal and comprises first and intermediate push-pull transductor stages and a final stage in which transductors are arranged in a bridge, an alternating output being provided by the final stage which is relative both in phase and magnitude to the input signal. In the arrangement shown in Fig. 4, the various transformer secondary wings 44, 45, 46 are associated with a single primary winding 47 connected to an A.C. supply at terminals 48. The alternating input signal is constituted by the combination of an error signal at terminals 40, 41 and an adjustable feed-back signal from a tachometer at terminals 76, 77. This signal is combined with the secondary voltages in transformer winding 44 to produce dissimilar D.C. output voltages from full-wave rectifiers 53, 54, which voltages are separately applied in opposition to series-connected transductor control windings 55, 56 and 57, 58 in the first stage. The control windings in the second and third transductor stages are similarly arranged and are energized by separate D.C. outputs of the respective preceding stage. The first and second stages each comprise a pair of autoself-excited bridge rectifying transductors, while the ultimate stage consists of four auto-selfexcited parallel transductors arranged in a bridge. (Both types of transductors are defined in British Standard 1523 : 1954.). In the final stage, the transductors are so arranged that each main winding in one bridge arm shares a common core with a main winding in the opposite bridge arm; for example, windings 69 and 70 are wound on one core and windings 68, 71 on another, the two groups of control windings 72, 73 each being associated with the cores forming opposite bridge arms. The arrangement of a pair of cores 81, 82 forming opposite bridge arms is shown in Fig. 6. The bridge is directly energized from the A.C. supply at 48 and the alternating output at terminals 42, 43 is derived from the balance points. Each transductor stage comprises bias windings which are energized from the supply over a rectifier 74, the bias to the first stage being adjustable at 75 so that overall balance may be obtained in the absence of an input signal. The final stage may alternatively be arranged as shown in Fig. 7 in which a pair of auto-self-excited parallel transductors are energized from a centre-tapped transformer 100. The transductor cores may be formed from a grain oriented 50 per cent nickel-iron alloy, the material for the final output stage having a substantially rectangular hysteresis loop, while the earlier stages require the characteristics of low loss and high initial and maximum permeability. The core material is in the form of insulated strip which is wound on a mandrel toproduce a toroid, square or rectangular shape. a number of transductor cores being moulded together by plastic in a stack after winding the various coils. Specification 660,105, [Group XXXVIII], is referred to.