Patent GB-768445-A (GB)
Title: Improvements in and relating to regulating systems for synchronous electric generators
IPC: H02P9/10
Filed: 1953-02-03
Abstract: 768,445. Automatic voltage control systems. GENERAL ELECTRIC CO. Feb. 3, 1953 [Feb. 8, 1952], No. 3036/53. Class 38 (4). The stability of an automatic voltage control system for an alternator is improved by controlling the output of a sub-exciter in accordance with a phase advanced signal proportional to the alternator voltage, and this signal is modified by a signal indicative of rotor transient oscillation, and this latter signal is either (1) the rate of change of alternator field current and the rate of change of alternator field voltage, or (2) the rate of change of alternator field current and the rate of change of alternator field flux, or (3) the component of alternator armature current which is in phase with the armature voltage, or (4) the rate of change of the power output of the alternator, or (5) the speed of rotation of the rotor, or (6) the angle between the voltage appearing across the external load and the internal generated voltage of the alternator. A signal proportional to the rate of change of alternator field current is obtained from transformer 24, Fig. 1, and a signal proportional to the rate of change of alternator field voltage is obtained by differentiating a signal proportional to the field voltage, this signal being tapped off potentiometer 21. The differentiation is effected by a network 22, 23 which has a time constant shorter than the period of change in excitation corresponding to the hunting frequency of the rotor. The two derived signals are added so that the current responsive signal is regenerative and the voltage responsive signal is degenerative with respect to the changes which produce them. The result of the addition is optionally passed through a ripple filter 27, amplified at 28 and then added to the conventional voltage regulating signal which is the resultant of a rectified signal proportional to the alternator output voltage and an opposing reference voltage. The combined resultant is amplified at 30 and passed via a cathode follower 31 to a network 32 which is operative to advance the phase of signals of rotor hunting frequency approximately 20 degrees more than the phase lag introduced by the time constants of the exciters and filters. The final signal is amplified at 33 and controls the excitation of the alternator 10 via subexciter 17 and main exciter 15. In a modification, Fig. 2 (not shown), the general arrangement of Fig. 1 is followed, but all the items of the block diagram are shown in circuit detail, the sub-exciter machine is replaced by a gridcontrolled rectifier, the phase advancing network is modified by the inclusion of a capacitor in series with the shunt resistor so as to introduce a phase lag at frequencies below rotor hunting frequency, and the stabilizing signal is proportional to the rate of change of field current (derived as before from a current transformer) and the difference between the field voltage (said to be proportional to the rate of change of flux linkages in the magnetic circuit of the alternator). In a third modification, Fig. 3 (not shown), the stabilizing signal is proportional to the component of alternator armature current which is in phase with the generator armature voltage, and is obtained by an electronic wattmeter circuit in which the valve anodes are energized in accordance with the magnitude of the armature current, and the control grids in accordance with the armature voltage. In a fourth modification, Fig. 4 (not shown), the stabilizing signal is proportional to rate of change of power and is derived from a coil movable in a magnetic field by a dynamometer wattmeter. In a fifth modification, Fig. 5 (not shown), the stabilizing signal is proportional to the speed of the alternator and is derived from a D.C. tachometer generator. In a sixth modification, Fig. 6 (not shown), the stabilizing signal is proportional to the angle between the voltage appearing across the external load and the internal generated voltage of the alternator and is derived by applying the output of a current transformer in the load circuit to two impedances which are stated to represent the impedance of the alternator and the impedance of the system, respectively vectorially adding and subtracting the voltages across these two impedances from the system voltage, squaring both resultants and applying them to the wattmeter circuit of Fig. 3 to provide the stabilizing signal.