Patent GB-784177-A (GB)
Title: Regulating system for an alternator with exciter field winding in series with alternator field winding
Inventor: RINGLAND WILLIAM LYLE
IPC: H02P9/32
Filed: 1955-08-05
Abstract: 784,177. Automatic voltage control systems. ALLIS-CHALMERS MANUFACTURING CO. Aug. 5, 1955, No. 22670/55. Class 38 (4). In a system for stabilizing the output of an alternator, an A.C. exciter driven with the alternator has its output rectified for selfexciting its own field in series with the alternator field, the level of excitation in the common field circuit being correctively varied by means responsive to alternator output variations for maintaining the output at a desired value. As shown, the alternator 5 has a rotor-mounted field 9 excited in series with the stator field 13 of an induction exciter 10 from the rectified exciter output derived from stator output windings 12. The exciter has a toothed rotor 20 driven with the alternator to provide an exciter output frequency equal to six times the alternator frequency. The common excitation in series fields 9, 13 depends on the load presented by self-saturating reactor pairs 14, 15, 16 in shunt with the field rectifiers 11 across the exciter output windings 12. Transformers 34, responsive to the alternator output voltage and associated with auto and boosting transformers 35, 36, energize non-linear ferro-resonance circuits comprising saturable transformer primaries 28 and condensers 30, the voltages across the condensers and across transformer secondaries 42 being rectified to provide opposed voltages across resistors 38, 43 representing the averages of the condenser and transformer voltages respectively. Any deviation of alternator output from a desired value, set by the characteristics of the non-linear circuits and by a tapping on resistor 43, results in a voltage across resistors 38, 43, representing the sense and magnitude of the deviation, which is applied to the common control winding 44 of self-saturating reactor pairs 48, the latter being energized over lines 50-52 from the output-responsive network 34, 35, 36 and having a D.C. output to the common control winding 26 of the reactor pairs 14-16, whereby their reactances are varied to cause corresponding changes in the excitation of fields 9, 13 so the output of the alternator is restored to the desired value. The averaging action in the non-linear circuits prevents over-regulation in the event of phase unbalance in the line load. Rectifier 32 and reactor 37 limit the voltage across resistors 38, 43 in a sense tending to decrease the excitatior. The system response is enhanced by injecting a rectified voltage representing the alternator output into the circuit of a common bias winding 21 for reactors 14-16 by means of a resistor 59, while hunting is reduced by energizing a common bias winding 57 of reactors 48 from a damping transformer 54 responsive to changes in field excitation. To ensure voltage build-up upon loss of residual flux in the exciter, a D.C. source 63 passes a bias current in field 13 when the main excitation voltage from rectifiers 11 is less than that of the source. The exciter load comprising the reactors 14-16 is arranged to be substantially resistive so that the voltage drop thereacross is in phase with the terminal voltage, this being a desirable condition for the regulating action of the exciter. A theoretical account of this action is given in the Specification. In a modification, Fig. 5 (not shown), the exciter field is wound on the rotor of an A.C. exciter, and both fields are energized by the auxiliary excitation source. Capacitors are connected across the exciter output windings for providing only the harmonic currents required by the rectifiers so that such currents are not provided by the exciter.