Patent GB-713633-A (GB)
Title: Improvements relating to electric generators
IPC: H02K23/36
Filed: 1950-05-30
Abstract: 713,633. Automatic control systems for exciting dynamo-electric machines. MACFARLANE ENGINEERING CO., Ltd., MACFARLANE, J. C., and MACFARLANE, W. I. Nov. 29, 1951 [May 30, 1950], No. 13400/50. Classes 35 and 38(4)] A self-excited D.C. generator used for controlling a variable which may be represented by an electric current, has a supplementary field comprising a saturated pole part and an unsaturated pole part carrying windings wound in mutual opposition and fed with the current representing the variable so that they neutralize each other at a predetermined current, the resultant armature output being used to control the variable in the required way. In its simpest form, Fig. 1, a pair of D.C. generators 13, 14 having respectively a saturated pole assembly 15 and an unsaturated pole assembly 16 excited by coils 17 and 18 respectively, both carrying the current representing the variable. The armature outputs are in opposition and any unbalanced voltage appears across terminals T. The self-excitation coil 21 is fed either in parallel with the load 22 or, as shown, in series with it, while transients are eliminated by means of a short-circuited coil 20. Instead of using two generators, a single machine having axially separated field cores acting in opposition on two parts of the same armature may be used. The two field members may be of salient or non-salient pole type and in the latter case the compensating windings are carried through 'slots in both cores interpoles being used if required. Instead of using axial separation of the core members, the saturated and unsaturated poles may be circumferentially disposed in each pole-pitch. A salient pole form of this embodiment is shown in Fig. 5 in which each pole-pitch contains four pole-cores, 16a, 15. and 16b comprising the main pole, and 24 acting as an interpole, armature-reaction being comuensated by coils 25 situated in the spaces between the pole-cores. As before, the pole core 15 is saturated, while the cores 16a. 16b between them provide the unsaturated core with polarities opposite to that of core 15. The cores 16a, 16b also carry the self-excitation coils 21 which are wound to produce the same polarity as core 15. In order to ensure build-up the stator core or only the saturated pole core 15 may be composed of some retentive material. In the latter case the pole core may be composed' of retentive stampings secured by a clamping loop of copper taking the place of coils 20. Fig. 11 shows how the machine may be used for controlling the voltage of a generator 30 by feeding the field coils 17, 18 on the saturated and unsaturated poles in series from the output. The resultant output of the machine 26 is used to feed the generator field winding 29, the series connected self-exciting winding 21 being designed to produce a sufficient excitation for normal load conditions. A transformer 33 connected across the field winding 29 and feeding an additional winding 36 on the unsaturated poles or spanning the interpolar axis may be used to improve the response to transients as described in Specification 593,817. By using rectifiers the voltage of an alternator may be similarly regulated, and shunts connected in parallel with the windings 17, 18 may be used to control the load current of a generator. Alternatively the machine may regulate its own current by feeding the load through a suitable impedance, e.g. the compensating winding, across which the windings 17. 18 are connected. A drooping characteristic for welding may be produced by allowing saturation of the relatively unsaturated pole part 16.