Patent GB-568137-A (GB)
Title: Improvements in or relating to turbo-generator installations
IPC: H02H5/08
Filed: 1943-06-15
Abstract: 568,137. Automatic control systems for turbo-generators. JACKSON, S. B. June 15, 1943, No. 9578. Drawings to Specification. [Class 38 (iv)] [Also in Groups III, XXVI and XL] To maintain optimum conditions of vacuum in a a turbo-alternator installation, the supply of cooling fluid to the condenser is automatically adjusted on each change of loading. The circulating pump is electrically driven from the alternator and a current transformer energizes the current coils of induction disc apparatus in accordance with the difference between alternator load and pump consumption, whereby a change in this difference initiates a progressive reduction in circulating fluid for an adjustable period which is automatically followed by a progressive increase until the nett output of the alternator ceases to rise, whereby the desired optimum condition corresponding to maximum nett output is reached. As described, the circulating pump is coupled to the pump motor through an electromagnetic variablespeed coupling, the excitation of which is varied to change the pump delivery. The excitation is supplied from the motor terminals through grid-controlled rectifying valves and the pump output is varied by a reversible electric control motor which adjusts the phase of the grid voltage of the rectifiers. The control motor is automatically caused to run to a zero position when the pump motor switch is opened and may be manually adjusted by push-button control after the pump motor has been started and when automatic control is not operative, to produce any desired vacuum. The control motor is of the split-field series type, the fields being supplied through separate rectifying valves having independent manual adjustment of the phase of their grid voltages, or through other means, whereby a higher effective voltage is applied to the motor when operating to lower the pump output than when raising it. A differential current transformer is arranged to yield no output current when the turbo-alternator is running unloaded with optimum (manually adjusted) vacuum. The current coils of inductive disc motors of an impulse-initiating device are in series with the secondary winding of this transformer. The impulse-initiating device is less damped than the other, so that it operates first when the alternator load rises. It comprises two perforated coaxial discs which normally jointly obtrude a light beam falling on a photo-electric cell. One disc is normally braked so that a change of nett alternator load will cause light to fall upon the cell and initiate current in a thermionic valve which operates a relay to charge a timing condenser to a predetermined voltage, whereby a selector switch becomes energized to start the control motor to reduce the sump output. The voltage across the armature of this motor causes the release of the brake and the coaxial discs return to the obturating condition to stop the impulse generation. The condenser is shunted by an adjustable discharge resistance to determine the period of reduction which is made sufficient to bring the vacuum below the range of optimum values. The secondary current of the transformer operating on the optimum control devices causes rotation of an induction disc carrying a mirror, whereby a beam of light is directed to one or other of two photo-cells on a platform coaxial with the disc. A rising current energizes one cell and thereby a valve, whereby a follow-up motor geared to the platform is operated. Simultaneously, an optimum control contactor is energized, whereby a reverse circuit for the control motor is prepared. When the timed reduction period is complete, the selector switch is deenergized and this reverse circuit closed, whereby the pump output is raised progressively at a slower speed than the reduction. When the nett generator output ceases to rise as a result of the increase in pump motor current, or a fall occurs in alternator load, the follow-up action reverses, the optimum control switch is de-energized and the increase in pump output and vacuum stops, a relay responsive to a fault in the alternator load circuit is adapted to prevent operation of the timing means, so preventing operation of the control system. The output of the pump may be raised by means other than a variable speed coupling and more than one pump may be controlled. Specification 566,589 is referred to.