Patent GB-1185578-A (GB)
Title: Improvements in Control Systems for Steam Turbine Power Plant
IPC: H02P9/00
Filed: 1968-08-02
Abstract: 1,185,578. Pressure regulating systems. GENERAL ELECTRIC CO. Aug. 2, 1968 [Aug. 16, 1967], No.36951/68. Heading G3R.  A pressure regulating system for a steam turbine power-plant which supplies steam to a process conduit comprises at least one turbine having an adjustable valve to supply steam to the process conduit; a second higher pressure steam conduit connected to the process conduit by an adjustable reducing valve; means responsive to pressure in the process conduit to provide an electrical command signal representative of the deviation of said pressure from a set value which is applied to first and second flow controllers which control the setting of the turbine valve and regulator valve respectively; and adjustable biasing means on the flow controllers to selectively vary the effects of the command signal on the controllers so that the most advantageous use may be made of the sources supplying steam to the process conduit. As shown a boiler 5 supplies steam to a single extraction turbine 1, a double automatic extraction turbine 2, and a non-condensing turbine 3driving generators 6, 7, 8 respectively. Control units 9-11 control turbines 1-3 respectively with regard to speed or load. Control units 9, 10 provide an integrated control of extraction pressures as well as loads by co-ordinated positioning of steam inlet valves 12, 13 and extraction valves 15, 16, 17. Control unit 11 may be a simple mechanical speed governor. Turbines 1 and 2 supply a high-pressure process line 15, also supplied direct from steam line 4 through reducing valve 4, and turbines 1 and 2 supply a low-pressure line 22 which is also supplied through a reducing valve 23 from the highpressure line 18. A pressure transducer 28 in lowpressure line 22 senses its pressure and feeds a proportional A. C, signal to a pressure translator 29 where it is compared with an A. C. signal representing the desired pressure set by knob 30. A D. C. error voltage output of the translator 29 proportional to the A. C. error voltage is fed to a regulating amplifier 31 whose proportion regulation may be changed by control knob 33. The command signal of amplifier 31 is fed to three flow controlling amplifiers 34, 35, 36 whose outputs are connected to the valve positioning control units 26, 24, and 25 respectively. Amplifier 36 is supplied through a gain adjusting potentiometer 37 and also from a positive adjustable potentiometer 39. Each of the amplifiers 34, 35 is fed directly with the error voltage and also from centre earthed adjustable potentiometers 41, 42, respectively. By adjusting control knobs 38, 40, 44, 48, the various steam sources e.g. 2, 3, and 18 may be actuated in any desired sequence or combination. For example if incremental flow control 38 is set so that the full error voltage is applied to amplifier 36 and base control 40 is set to the earth position, and if a small negative bias is applied to amplifier 35 from potentiometer 42 and a larger negative bias is applied to amplifier 34 from potentiometer 41, the low-pressure line will be supplied from its sources in the following sequence, turbine 3, turbine 2 and pressure reducing valve 23 as the command signal increases. A similar control system (not shown) is provided for the highpressure conduit 18.