GB918779A - Improvements in governing system for reheat steam turbine powerplant - Google Patents

Abstract

918,779. Steam turbine plant. GENERAL ELECTRIC CO. Aug. 6, 1959 [Aug. 22, 1958], No. 26904/59. Class 110 (3). A steam turbine plant comprising a steam generator feeding a turbine stage which discharges through a reheater and intercept valve to a further turbine stage, has starting valves to admit limited quantities of live steam directly from the steam generator to the inlets of the turbine stages and actuating means for progressively closing the starting valves as the intercept valve opens during starting. The plant shown comprises a super-pressure turbine section 3, the exhaust from which passes through a reheater 43 to a high-pressure turbine section 4. The turbine section 4 discharges through a reheater 42 to two intermediate pressure sections 4, 5 arranged in parallel which discharge through low-pressure turbine sections 7, 8 to condensers. The turbine sections 3, 5, 7 form a first turbine unit 1 and the sections 4, 6, 8 a second turbine unit 2. Steam is fed to the turbines from a boiler 44 and superheater 47. Valves 13, 14, 15 are intercept valves arranged to shut off steam to the turbine sections 4, 5 and 6, respectively, in an emergency. The plant is started as follows. When the steam generator and turbine are cold, the boiler feed pump 45 is started up and circulates cold water through the boiler 44, superheater 47, super high pressure turbine by-pass valve 50, conduit 51, water separator 52, and condenser hot well 54. When 30% of the rated flow is established, the boiler is fired and the water pressure rises to the full rated pressure. The by-pass 50 is controlled by the pressure and temperature at the superheater outlet. As the temperature rises a certain amount of the water flashes into steam as it passes through the valve 50. The water is separated from the mixture in the separator 52 and returned to the condenser hot-well 54. The steam passes through conduits 55, 56, highpressure reheater 43 and conduit 57 to the high-pressure turbine by-pass valve 58 and then through conduit 50 to the low-pressure reheater 42. This reheater discharges through a lowpressure turbine by-pass valve 61 to the condenser 62. As the heat input to the boiler 44 increases, water is injected into the desuperheating spray chambers 63, 64, 65 to prevent damage to the piping and condenser tubes. During this process the by-pass valves 58 and 61 are adjusted manually so as to gradually raise the pressures maintained in the high and lowpressure reheaters 43, 42. To warm up the turbine sections 3, 4, a small amount of warming steam is admitted to the discharge ends of these turbines by manually opening the valves 66, 67. After warming, the valves 66, 67 are manually closed and the boiler stop valve 70, main stop valve 48, high-pressure reheater stop valve 72 and the low-pressure reheater stop valves 73, 74 manually opened. The adjustable loadlimiting device 35 is now backed away from the right hand end of lever 20 which rises and causes rack 25 to rotate cams 75, 79, 77, and open the pilot valve 10 in the main control valve 9 and two starting valves 11, 12. This admits live steam into the turbine sections 3, 4, 5 and through conduit 38 to the turbine section 6. Orifices 39, 40, 78 limit the flow. The quantity of steam is so selected that the heat generated in the respective turbine sections by turbulence is removed. When the governor 28 reaches the rated speed the generator driven by the turbine is connected to an A.C. network so that when the synchronizing device 29 is actuated to open the valves 11, 12, 13 any tendency for the turbine to overspeed is prevented. This action continues until the cam-shaft 16 fully opens the starting valves 10, 11, 12. At this point the cam 76 begins to open the intercept valve 14, cam 21 the intercept valve 13 and cam 22 the intercept valve 15. At the same time as valves 13, 14, 15 begin to open, the valve actuating rod 36 begins to lift the main governor valve 37. Further actuation of the synchronizing device 29, begins to close the starting valves 11, 12 and to open the intercept valves 13, 14, 15. This operation continues until the valves 11, 12 are completely closed and the valves 13, 14, 15 fully open. This is the normal operating condition. During starting the by-pass valve 50 has been acting to maintain the discharge pressure at the superheater outlet. By the time 30% load is reached by-pass valve 50 is completely closed. Under these conditions, the by-pass valves 58 and 61 are completely closed. All the boiler flow is now passing through the main inlet valve to the turbine 3 and through the intercept valves 13, 14, 15 to the turbines 4, 5, 6. The intercept valves 13, 15 are actuated by the main governor 28 acting through links 30, 31, 32. The valves 13, 15 may also be operated by the pre-emergency governor 34 if the speed for which the governor is set is exceeded.