GB1255239A - Improvements in or relating to ferroresonant voltage regulator devices - Google Patents

Abstract

1,255,239. Automatic voltage control. NORTH ELECTRIC CO. Sept. 5, 1969 [Oct. 7, 1968], No.44136/69. Headings G3R and G3X. A ferroresonant voltage regulator comprises a transformer having a three-limb core whose centre limb 20 carries the A.C. supplied input winding 28, output windings 34A, 34B supplying loads 60A, 60B, a winding 40 supplying a capacitor 48 which is resonantly discharged through an inductor 50 by anti-parallel connected SCRs 52, 54 and a feedback winding 64 which supplies the control circuit determining the firing instants of SCRs 52, 54, the winding 28 being separated from its fellows by a magnetic shunt 24 which forms airgaps with the two outer limbs, Fig. 1 (not shown). The firing points of the SCRs 52, 54 are automatically varied to hold constant the time integral of the voltage over each half cycle of the output, firing occurring near the end of each half cycle when the portion of the core carrying the windings 34, 40 is driven into saturation. An integrator circuit 80 provides a signal representative of the time integral of the voltage to a level detector 82 supplied via members 118, 122, 124 with a reference signal, the arrangement being such that when a predetermined relationship between these two signals is reached, an output pulse is applied to a pulse amplifier 86 and thence to SCRs 52, 54 via the pulse transformer 134. Members 122, 124 also form a reset circuit 88 for the discharge of integrator capacitor 114 after each pulse generation, the instant of which is automatically varied with variations of the A. C. supply to winding 28 (and hence of the time integral of the voltage) to maintain the output voltage of windings 34A, 34B constant. To minimize the effect of changes of temperature and frequency, a further feedback signal is applied to the level detector 82 from an amplifier 152 which receives the output of a voltage detector 148 comprising a differential transistor amplifier 170, 172 supplied with a reference signal from members 164, 166 and with a signal obtained from the winding 64 via members 154, 156, 158, 160, 162. This feedback signal has the effect of altering the level set by the reference circuit 118, 122, 124. The output windings 34A, 34B may supply A. C. or D.C. voltages, which may be sensed and compared with a reference to provide a further feedback signal for transmission to the level detector via an amplifier, Figs. 3A and 3B (not shown). The sensed value may be RMS, peak or rectified average. In Fig.4A the inductor forms part of the structure of the ferroresonant transformer, whose centre limb 220 has two magnetic shunts 224, 245, an input winding 228, a load winding 234, a feedback winding 264, a capacitor winding 240 and a winding 247 shunted by anti-parallel connected SCRs 252, 254 fired by the control circuit 280. The method of operation of this embodiment is discussed, Fig. 5 (not shown).