Patent GB-1307784-A (GB)
Title: Turbine installation safety circuits
IPC: F01D21/20
Filed: 1971-04-19
Abstract: 1307784 Controlling turbines BROWN BOVERI & CO Ltd. 19 April 1971 [31 March 1970] 25586/71 Heading FIT Two stage turbine installation has both stages driving a single shaft and a pressure vessel between the stages, two safety circuits in parallel, each responsive to its own safety devices for detecting overspeeding of the shaft and excessive pressure in the vessel, protection equipment controlled by the safety circuits and operating to reduce the vapour input to the vessel and the stages if one of the devices detects either overspeed or over-pressure, separately operable test systems for the respective safety circuits, and means to prevent actuation of the protection equipment as a result of the operation of the devices of either one of the safety circuits, the other safety circuit remaining effective during the testing period. Steam from a generator 1 is fed to a H.P. turbine 3 and then through a re-heat line 4 to a pressure vessel 6 and a L.P. turbine 5. Mounted on the turbine shaft are two over-speed sensing devices 8 and 9. The pressure vessel can be isolated by two hydraulically operated quick-acting valves 13 and 14, normally held open by hydraulic pressure in a line 15, which can be exhausted by opening a valve 17, which is normally held closed by hydraulic pressure from a line 20. The pressure in the line 20 is controlled by two parallel safety circuits 21a and 21b, which receive oil under pressure via valves 34a and 34b. A low-pressure line 23 is connected to the two safety circuits but is normally isolated therefrom by closed gate-valves 33a, 33b, 26a and 26b, of which the valves 33a and 33b are controlled by the sensors 8 and 9, and the valves 26a and 26b are responsive to pressure sensors 24 and 25 communicating with the line 4 upstream of the pressure vessel 6. The testing system for the sensors 24 and 25 comprises a high-pressure line 32 connected to the sensors through valves 28a and 28b in series with motor driven valves 30a and 30b. To isolate the safety circuits as required during testing there are two valves 41a and 41b which are mechanically interconnected by a push-rod 40, and are biased by springs 43. In the normal operating position both the test circuits communicate with the line 20 of the protection equipment. The valve 41a being held open by admitting hydraulic pressure to act on a piston 42a, by opening a solenoid operated valve 36a. The pressure can be exhausted by opening a valve 37a mechanically connected to the valve 36a. The valve 41b is similarly operated, Since both valves 41a and 41b are open, pressure from the line 20 holds valve 17 shut, so that valves 13 and 14 are open. The safety circuits are tested individually e.g. circuit 21a is tested by energizing relay 39a to close valve 36a and open valve 37a, thus closing valve 41a and leaving valve 41b open. The over-speed device is artificially moved to indicate excessive speed, so that valve 33a opens, as indicated by a fall in pressure in line 21a. Valve 26a is tested by closing valve 29a, opening valve 28a and then progressively opening valve 30a until unit 24 causes valve 26a to open, which again is indicated by a pressure drop in line 21a. The remaining safety circuit is tested is a similar way.