GB910812A - Improvements in or relating to compound excitation systems for rotary generators - Google Patents

Abstract

910,812. Automatic voltage control; alternators. MULLARD Ltd. May 16, 1961, No. 17795/61. Classes 35 and 38 (4). In a compound field excitation arrangement for a rotary generator, a cycling switch connected across a compounding source intermittently bleeds excitation current over a part of the load current range of the generator up to a predetermined short-circuit current, the duty-cycle of the switch being varied in dependence upon the value of the load current. In an embodiment, Fig. 8, a field 5 of a rotary generator is supplied by a voltage dependent source S 1 , not shown, and a compounding source S 2 . An intermittent bleed through a silicon controlled rectifier 21 is made by a pulse at fixed intervals from a unit 39 synchronized to a square-wave oscillator 30. The rectifier 21 is switched off by silicon controlled rectifiers 23, 24 rendered conducting by timing pulses applied in sequence. The rectifier 23 is made conductive simultaneously with the rectifier 21 by a pulse from unit 39. A commutating condenser is discharged by the rectifier 24 after a delay, determined by a signal from a magnetic amplifier MA or a delay unit 36 through an " OR " circuit 34 and pulse control 37. The magnetic amplifier MA is energized with a square-wave signal from the oscillator 30 and has a control winding 27 energized in dependence on the current-bleed and a reference winding 28 energized from a battery 29, to produce a square wave of double the oscillator frequency having a delay dependent on the current in the control winding. 27. A signal from the oscillator 30 is also fed to a monostable trigger multivibrator 36 acting as a time delay. The time-delayed signal and the signal from the magnetic amplifier are fed to the "OR" circuit whereby the first arriving pulse controls the firing time of the rectifier 24. In another embodiment, Fig. 10, for an alternator 1, a voltage-dependent excitation current is derived by a device S and fed to a field winding 5 and a compounding excitation current is fed to the field winding from a current transformer 6 through a full-wave rectifier S2. Separate intermittent current bleeding silicon controlled rectifiers 41-43 are provided for each phase controlled by separate magnetic amplifiers MA(1)-MA(3) each provided with a pulse. producing circuit 48(1)-48(3). The quenching circuit of Fig. 8 comprising rectifiers 23, 24 is not necessary since the rectifiers 41-43 are supplied with alternating current. Specification 898,281 is referred to.