296,481. Electric Construction Co., Ltd., Hunt, L. J., and Tonkinson, W. June 7, 1927. Rotary transformers; exciting; dynamos, regulating; motors, controlling; windings. - An alternating-current dynamo-electric machine has a single continuous-current distributed exciting winding presenting different paths for the flow of current for setting up two fields of different pole numbers, the winding being so arranged that by varying the current entering at one or more of its terminals the axis of at least one of the fields may be angularly displaced gradually. The invention is particularly applicable to frequency converters, wherein variation in the relative angular positions of the field is necessary for altering the load, and the application to double current generators and motors supplied with two currents at different frequencies is referred to. Figs. 1 and 2 show a field winding for a converter giving fields of eight and four poles. The winding is a single layer winding with twelve coils connected as a double-parallel star, the exciter A for the eight pole field being connected to the star terminals x, y, z, and the exciter B for the four pole field being connected between the neutral points o1, o2. The resultant polarities and current distribution in the conductors are shown in Fig. 1. If the terminal z is disconnected from the exciter A, the axis of the eight pole field is displaced by half a slot which as shown in Fig. 3. By connecting the terminals x, y, z in various ways to the brushes of the exciter A, the eight pole field may be displaced progressively until the axes of the two fields again coincide, the displacement being analogous to that of a rotary field produced by polyphase currents. A more gradual movement of the field may be obtained by the introduction of variable resistances into the branches x, y, z. The Specification describes also a three-phase winding arranged partly as a double layer winding and a winding arranged wholly as a double layer winding, the purpose of these arrangements being to improve the field distribution. A similar winding is also described having sixteen and twenty poles suitable for use in a frequency converter operating on frequencies of 50 and 40. Figs. 20 and 21 illustrate the application of the invention to a winding similar to an alternating current twophase winding. The winding is in the form of two parallel connected squares, and the exciters A, B produce the currents for the eight and four pole fields respectively. By varying the currents flowing in at the terminals w - - z, displacement of the eight pole field is effeeted. A similar two phase winding is described producing fields of sixteen and twenty poles. The positions of both fields may be adjustable, and two exciters may be used to supply the adjustable field so that the necessary variation may be obtained by adjusting the fields of the exciters. The input and output sides of the converter may be wound for different numbers of phases. The stator of the converter may be provided with two alternating current windings or a single winding may be employed. Fig. 24 shows a suitable winding for use with two fields having pole numbers in the ratio of 2 : 1, connected to a three-phase transformer. The double arrows represent the instantaneous direction of the currents in the limbs X, Y, Z, corresponding to the field of the larger pole number and the direction of the currents corresponding to the smaller pole number is represented by the single arrows. The terminals I, II, III for the lower frequency are connected to the midpoints of the transformer primary winding x1 y1, z1, and the terminals 0, P, Q for the higher frequency are connected to the secondary winding x2, y2, z2. Fig. 25 shows another stator winding in connection with a transformer, X, Y, Z, being the terminals for the higher frequency currents, and I, II, III the terminals for the lower currents. According to the Provisional Specification. the two squares in the two-phase type of winding may be connected in series with respect to the elight pole exciter, and the invention can be applied to machines in which it is not necessary to vary the relative positions of the fields, in which case both exciters can be permanently connected to the field winding, or a single exciter may be employed. The invention is stated to be applicable also to frequency converters comprising two separate machines, in which the field of one of the machines is adjustable angularly. Specifications 16170/09, 9260/13, 24837/14, 124,018 and 167,242 are referred to.