Patent GB-694993-A (GB)
Title: Dynamo-electric machines
IPC: H02K23/40
Filed: 1951-05-28
Abstract: 694,993. D.C. generators. SOC. D'EXPLOITATION DE BREVETS. May 28, 1951 [May 26,1950], No. 12514/51. Class 35. A self-regulating D.C. generator comprises a field structure having a constant magnetic comparison flux in a saturated or permanent magnet pole X and a variable flux of the same polarity in a pole Y whose value depends on the output voltage to be regulated, any inequality in the strengths of these poles producing circulating currents in such a sense as to correct the terminal voltage, the saturated pole being provided with a shunt path so that the main flux, and therefore the output of the machine, may be varied without altering the saturation. The field structure has four main poles X, Y, Z, Q, while the armature 2 has a four-pole multiple winding with conventionally arranged brushes 3, 4, 5, 6. The total working flux in the machine is varied in spite of the saturated state of the pole X by means of magnetic shunts on this pole. In the form shown in Fig. 1 these comprise extended pole-tips 11 having leakage air-gaps 12 to the machine core. In a modification, Fig. 2, the pole X may be of multiple form having slots 13 on either side of a saturated core 7a and leaving radial shunting projections 11a. In a further modification, Fig. 3, a pole has a pair of slots 14 transverse to the machine axis, the magnitude of the flux shunted being adjusted by plungers 16 having adjustable air gaps 12b to the end parts 11b, the main pole flux being controlled by a plug 17. If windings 8, 9 on poles X, Y are energized in dependence on the same condition, e.g. supply voltage, the pole X carries a substantially fixed flux owing to its saturation while pole Y may carry a flux more or less than that in the pole X depending on whether the voltage is high or low. This produces an unbalanced flux which has the effect of inducing a difference of potential between the brushes 3, 4 which are normally at the same voltage. An additional flux produced by additional ampere-turns dependent on the deviation from the required output voltage may be superimposed on the four-pole reference flux by means of the shunts 11. When the additional ampere-turns are distributed equally on poles X and Y the total machine flux increases while remaining symmetrically distributed, any departure of the terminal voltage from the correct value producing a voltage between brushes 3 and 4. If the ampere-turns of windings 8 and 9 are not equal owing to different pole reluctances, the additional ampere-turns must be distributed between poles X and Y in a like proportion. The reluctance of pole Y may be varied by means of spacers 15 and that of the shunt path to pole X by varying the air-gap 12 of the shunt 11, e.g. by means of the screw plungers 16 shown in Fig. 3, the reference flux of the machine being varied by means of the screw 17. Fig. 5 shows a circuit for a self-regulating generator in which the primary brushes 3, 4 are connected together directly by a conductor 19 or through a coil lying on pole Q, and feeding one output terminal 20, while the secondary brushes 5, 6 are joined by a winding 23 on the pole X with a centre-tap connection to the other output terminal 22. The windings 8 and 9 are energized by the output voltage and any deviation from flux balance owing to high or low terminal voltage causes a circulating current 11 between brushes 3, 4, which in turn gives rise to a current 12 between brushes 5, 6. This current, in passing through armature conductors and coil 23, produces the additional four-pole flux required to correct the voltage output of the machine. The output voltage may be adjusted by means of a magnetic device shown in Fig. 3 or by a variable resistance 25 in the field winding 9, and inequalities in the reluctances of the poles X, Y may be compensated for by shunting the brushes 5, 6 with an adjustable resistor 26 or by altering the number of turns on winding 23. Interpoles may be provided with coils carrying the load current and circulating current 12. If desired, the shunts 11 of Fig. 1 or 11a of Fig. 2 may also act as interpoles, and in a modification a single winding may be used to excite the main pole X and a pair of interpoles. It is described how the machine may be used as an exciter regulating the voltage of a main machine. Specification 669,573 is referred to.