Patent GB-799466-A (GB)
Title: Control system for constant frequency induction alternator
Inventor: POLASEK KARL
IPC: H02P9/42
Filed: 1956-10-23
Abstract: 799,466. Induction generators. AERO MATERIEL AKTIEBOLAG. Oct. 23, 1956, No. 32253/56. Class 35. In a modification of the exciting arrangement for an induction alternator described in Specification 773,867, the rate of response is increased, thus protecting the source of the control frequency and voltage from overload. The alternator comprises two induction generators G1, G2 having rotors on the same shaft and mutually displaced stators, and is excited by the control oscillator O and condensers C through saturable transformers T1, T2 respectively, the coupling of these transformers being controlled in dependence on the circuit conditions. The coupling between stator and rotor of machine G1 is controlled by a presaturating winding 10 fed with the differential voltage from a tachometer generator 26 and rectifier 13, and an appropriate part of the line voltage from rectifier 14 and potentiometer 17. This arrangement provides automatic voltage compensation for speed. The presaturating winding 11 of transformer T1 is fed in parallel with the winding 10, and permits coupling of the source O to 'the alternator when this has attained a suitable speed. The extent of condenser coupling through saturable transformer T2 is controlled in dependence on the phase and value of the currents in the load line and control circuit by means of current transformers T1 and T3 respectively. These transformers are both connected in two lines and are connected back to the third line through rectifiers. The secondary winding 22, 23 of transformer T1 are thus connected through rectifiers 24, 25 and symmetrical saturating windings 18, 19 of the transformer T2 to the third line, thus acting as a phase discriminator with respect to the machine voltage and gives a measure of the energy output of the machine. Alternatively, the discrimination may be with respect to the oscillator voltage. Similarly, the secondary windings 38, 39 of transformer T3 may be connected to act as a phase discriminator, but as shown feed the primary winding of a transformer T4 whose secondary windings are centre-tapped and connected in a rectifier bridge across the remaining phase of winding 2 of control transformer T1, this producing an oscillator-phase discriminated output for saturating winding 8 on transformer T2. If desired, the windings 18, 19 may be similarly replaced by a single winding. A third presaturating winding 28 on the transformer is fed from the machine terminals through rectifier 14 and adjustable resistance 27, and is thus responsive to line voltage. Thus the coupling of transformer T2 is automatically adjusted to control the excitation current from condensers C in. dependence on the load to maintain the voltage constant. Transformer T3 protects the source O from overload surges, and also corrects the excitation for frequency deviations by feeding beat-frequency currents into the discriminating transformer T4 and so controlling transformer T2 by winding 8 to adjust the capacity currents rapidly. The speed of operation may be improved by using the rectified output of transformer T3, instead of part of the rectified output voltage, to feed the saturating winding 11. Transformer T2 may have a single winding fed with the sum of the voltages of the four windings shown. In a further modification, the oscillator is connected through a unidirectional saturable reactor to the condenser bank to form a single unit connected to the generator through a further saturable reactor, these reactors being controlled as before, by phase discriminated current.