Patent GB-921294-A (GB)
Title: Control system for electrical generating units
IPC: H02P9/00
Filed: 1960-09-12
Abstract: 921,294. Automatic control systems for electric generating units. LEEDS & NORTHRUP CO. Sept. 12, 1960 [Nov. 13, 1959], No. 31352/60. Class 38 (4). A system for controlling a generating unit including an electrical generator 13 driven by a prime mover 12 supplied by a vapour generator 11 comprises means for producing at least two error signals representative of the actual deviation of two of the interdependent operating variables-generator output, vapour pressure and vapour temperature from the required magnitude thereof, a first control means responsive to the effective sum of said signals for varying the rate of supply of fuel to the vapour generator, and a second control means responsive to the effective difference of said signals for varying the feedwater input to the vapour generator or the vapour input to the prime mover. As shown, a signal G, e.g. from a wattmeter 19, representative of the output of the generator 13 and a signal G B  set upon a dial 31 to represent the desired output are compared in a comparator 21 to produce an error signal EG which, modified by a coefficient K 1  introduced by an attenuator 22, is applied to a combining device 23 in the input circuit of the fuel controller 17 of the vapour generator, and which, modified by a coefficient K 3  introduced by an attenuator 24 is applied to a combining device 25 in the input circuit of the throttle controller 16 of the prime mover. Similarly, an error signal E p , derived from a comparator 28 comparing the actual vapour pressure P, sensed at 26, with the required pressure P R  set on the dial 32, is modified by coefficients K 2  and K 4  and applied to the devices 23 and 25, respectively, the arrangement being such that device 23 adds the signals so that the input signal to controller 17 is K 1 E G +K 2 Ep and device 25 combines the signals subtractively so that the input signal to controller 16 is K 3 E G  - K 4 Ep. The generationerror signals thus tend to change the rate of fuel supply and rate of vapour flow in the same sense and the pressure-error signals tend to change these rates in opposite senses. Thus, if generation must be increased controllers 16 and 17 call for increased throttle opening and increased fuel supply; if vapour pressure must be increased the signal E P  as applied to controllers 16 and 17 calls for decreased throttle opening and increased fuel supply; if fuel is deficient, both pressure and generation will be low, so controller 17 in response to the sum of the error signals calls for increased fuel supply, but controller 16, responsive to the difference of these signals which in this case is effectively zero, makes no adjustment to the throttle opening; if the throttle opening is insufficient, the generation will be below its set point and the pressure will be above its set point, so that the sum of the error signals appearing at controller 17 is effectively zero and the difference of the signals applied to controller 16 is of finite value calling for increased throttle opening. In a vapour generator of the oncethrough type, the directly-controlled variables may be the generator output and the vapour temperature (Fig. 3, not shown), or the vapour temperature and vapour pressure (Fig. 4, not shown), or the arrangement may be a composite of generation/pressure, generation/temperature and pressure/temperature systems whereby the interaction of the control of any one of these variables upon any of the others is substantially eliminated (Fig. 5, not shown).