GB1411814A - System and method for operating a steam turbine with independent overspeed protection - Google Patents

Abstract

1411814 Steam turbines WESTINGHOUSE ELECTRIC CORP 6 Oct 1972 [14 Oct 1971] 46125/72 Heading F1T A steam turbine plant has an overspeed protection arrangement comprising three separate speed sensing systems and logic circuitry such that if any two of the sensing systems indicate a potential or actual overspeed condition then turbine steam flow control valves are closed. In Fig 1B a nuclear heated steam generator 102, 103 supplies steam through stop and governor valves 106, 108 to an H.P. turbine 110 and thence through a reheater (116) Fig. 1A (not shown), stop and interceptor valves (120, 118) to L.P. turbines (112, 114). The turbines drive an electric generator (122). In addition to the speed and other sensors controlling the steam valves during normal operation the plant includes three independent speed sensors 124-1, -2, -3 each with an associated check circuit 138, 140, 142. Each of the latter includes Fig. 2 (not shown), a comparator (210) to compare the sensed speed with an overspeed reference, e.g. 111% of synchronous speed, and a delay arrangement (220, 222) to sense any abrupt change in turbine speed, together with testpoints to check operation of the circuitry. Check circuits 138, 140, 142 are connected via relays 146, 148, 150, 152 &c. to a logic circuit 144 which includes duplicate AND-gates (172, 176) Fig. 4 (not shown), which operate to close the steam flow valves if a minimum of two check circuits emit signals indicating actual or potential overspeed or failure of the sensing system power supply. Thus it is possible to check operation of any one of circuits 138, 140, 142 during plant running without reducing overspeed protection. The steam flow valves 106, 108, (118, 120) are positioned by hydraulic actuators 130, 132, (136, 134) respectively and when the AND-gates (172, 176) emit overspeed signals solenoids 50, 51 operate to open valves 506, 508, Fig. 5, to cause rapid dumping of operating oil from each actuator cylinder 500 into a receiver 510, the steam valve thus closing under the action of spring 518. Receiver 510 is of heavy steel and has an associated shield (524, 526) Fig. 6 (not shown), to protect valves 506, 508 from turbine fragments. The receiver may include a blowout disc (528). Normal running of the plant may be controlled by a digital or analogue computer which may also be used to perform the function of check circuits 138, 140, 142 and of logic circuit 144.