Patent GB-913053-A (GB)
Title: Improvements in or relating to transformer arrangements
Inventor: WILLIAMS FREDERIC CALLAND
IPC: H01F29/12
Filed: 1958-04-08
Abstract: 913,053. Transformers; induction machines. NATIONAL RESEARCH DEVELOPMENT CORPORATION. April 2, 1959 [April 8, 1958], No. 10948/58. Classes 35 and 38 (2). A polyphase transformer having its primary and secondary accommodated in substantially parallel slots in relatively movable linear or concentric cylindrical cores is arranged to give a multiphase output and one or more of the physical or electrical parameters of the primary and of the secondary winding is proportional to the logarithm of another parameter of the construction so that relative movement between the primary and secondary windings varies the voltage at the output terminals or the phase difference between them. The transformer supplies an induction motor enabling variation of speed and may be constructed integrally with it. Alternatively, it may supply the magnetizing current of an induction generator. The primary winding arranged like the stator winding of an induction motor to give a moving magnetic field is shown flat at 12 in Fig. 7, the core being only partially wound and the slot distance from the left-hand end being proportional to the logarithm of the slot number (10 to 89) from that end. The slots enclosing the secondary bars 14 are similarly arranged the phase increment per bar being 18 degrees. Relative movement between primary and secondary then alters the phase difference between the secondary bars, the position shown in Fig. 8 giving a phase difference of 9 degrees per bar. Fig. 9 shows the transformer with its primary drawn flat in two alternative positions 20 and 201 and its secondary bars 21 connected to the windings 23 of the stator 24 of an induction motor having a squirrel-cage rotor 25. The stator 24 is then supplied with a travelling field by the transformer secondary, the phase increment per bar, and hence the field velocity, depending on the relative positions of the transformer primary and secondary either of which can be adjustable. The secondary winding may be arranged logarithmically over part of its length only by arranging for a complementary part of the motor stator winding to be arranged logarithmically (Fig. 13, not shown). Fig. 11 shows one arrangement with transformer secondary 40 and motor stator 41 on base-plate 42, the position of primary 45 being adjustable by handle 49 and the motor drive being taken from pulley 50. The rotor can be external. Fig. 19 shows a combined arrangement in section, the core stampings of transformer secondary 85 and motor stator 86 being clamped between end-plates and mounted on common non-magnetic rods 91. The bars 93 forming the secondary winding, stator winding and interconnections therebetween are shown together with the short-circuiting rings 94, 95. An alternative mechanical arrangement (Fig. 16) comprises a central squirrel-cage rotor 60 surrounded by a cylindrical member 61 wound on the inside to form the motor stator and the outside wound to form the transformer secondary. The transformer primary is wound logarithmically on outer member 62, speed variation being obtained by relative movement of 61 and 62. Alternatively, the transformer and motor may both be linear. The secondary may be shortened instead of the primary and if it is connected to stator bars over part only of the stator periphery, the stator iron may be removed from the remaining part or it may be fitted with shorting rings 26 (Fig. 14, not shown), to enable the machine to run at speeds intermediate even pole number speeds. The effect of a short-circuited section on the stator can be obtained by shorting rings on the unwound part of a primary core having a shortened primary. It is stated that the shorting effect can be eliminated in the top speed position by having an unwound part of the secondary circuit opposite the shorted primary section (Fig. 17, not shown). Figs. 22A-22G show embodiments of the transformer with logarithmic slotting in primary and secondary circuits, the arrangement in Fig. 22C comprising primary and secondary windings arranged in two symmetrical parts to give a magnetically-balanced arrangement. Suitable designs of motor rotors and stators to suit these transformer constructions are also described (Figs. 23A-23E, not shown). Logarithmic distribution of the primary field may be secured with evenly-distributed slots by using a decreasing number of slots per pole (Fig. 12, not shown), or by mixing the phases of supply in the slots (Figs. 20A, 20B and 20C, not shown). Alternatively, the primary may have two sets or more of windings with different numbers of poles in the same slots, the slots being arranged logarithmically (Fig. 21) with different sections brought into operation at different times. A variable ratio transformer can be obtained by using evenly-distributed slots and a constant pole pitch while increasing the number of turns per slot logarithmically as shown, by the top line of numbers in Fig. 18. By using a primary having the winding distributed logarithmically both in number of turns and pole pitch and a secondary having ring windings similarly distributed a variable number of phases as well as a variable ratio can be obtained. Specification 913,054 is referred to.