Patent GB-1188911-A (GB)
Title: Vapour Turbine Control Arrangement.
IPC: F01D17/18
Filed: 1968-10-09
Abstract: 1,188,911. Elastic-fluid turbines. TOKYO SHIBAURA DENKI K.K. Oct. 9, 1968 [Oct.14, 1967], No. 47849/68. Heading F1T. [Also in Division G3] A steam or other vapour turbine having circumferentially spaced vapour admission nozzles with corresponding control valves each actuated by a hydraulic servomotor operated by a pilot valve has a cam-shaft carrying cams for full arc admission control and partial arc control operating the pilot valves through lever means in response to a turbine speed governor and means for selectively switching the operation of the control valves from full arc control to partial arc control and vice versa. In the arrangement shown, a steam turbine has several admission control valves 10 each associated with a corresponding one of several circumferentially spaced nozzles. Each valve 10 is actuated by a hydraulic servomotor 12 operated by a pilot valve 13 controlled through a lever system from a cam-shaft 23 rotated by a rack 21 and pinion 22 in response to the turbine speed governor. The cam-shaft 23 carries pairs of cams, each pair 24, 25 &c, being associated with a corresponding control valve 10 and comprising a cam 24p, 25p &c. for partial arc nozzle control and a cam 24f, 25f &c. for full arc control. All the full arc control cams have the same shape and are fixed to shaft 23 with the same phase relationship so that during full arc running all the valves 10 open in unison and to the same degree. However, the partial arc cams do not have the same shape since, during partial arc running, they control the sequential opening of valves 10. Considering cam pair 25, the partial arc cam 25p can be engaged by a follower carried by a lever 26p pivoted at 27p. The lever 26p is coupled through a rod 29p to a piston 28pa of a hydraulic motor cylinder 28p whereby the cam follower can be caused to engage its cam 25p selectively whenever necessary. The same arrangement, denoted by reference letter f instead of p, is provided for the follower of full arc cam 25f. A solenoid actuated change-over valve 30 allows the flow of hydraulic fluid selectively to one or other of the motors 28p, 28f so that the associated follower is pulled into engagement with its cam. Levers 26p, 26f are coupled through rods 32p, 32f and relief springs 33p, 33f to opposite ends 31p, 31f of a floating lever 31 whose midpoint 31c is connected through further linkage with the pilot valve 13. The ends 31p, 31f of lever 31 are provided with hydraulic lock cylinders 36p, 36f coupled respectively thereto by rods so as to enable these ends to become, selectively, stationary pivotal points. The supply of hydraulic fluid to lock cylinders 36p, 36f is controlled by relief valves 37p, 37f the leakoff from which is regulated by valves having stems with racks 39p, 39f engaging pinions 40p, 40f on a shaft 41 driven by a motor 42. The relief valves 37p, 37f are arranged so that as one opens the other closes and vice versa. The lock cylinders 36p, 36f are constructed so that when a relief valve 37p, 37f closes to cause hydraulic fluid to flow to a respective lock cylinder, a pair of pistons (361, 363), Figs.2(a), 2(b) (not shown), in the cylinder are urged apart to lock the piston rod (364) connected to the respective end 31p, 31f of lever 31 in its mid-stroke position. The opposite end of the lever 31 is free to follow the motion of its associated control cam 25p, 25f and hence to actuate the pilot valve 13. The relief springs 33p, 33f, illustrated in greater detail in Figs. 3(a), 3(b) (not shown), permit the locked end of lever 31 to remain in the same position even when its associated follower is in engagement with its control cam. The linkage 18 between the pilot valve 13 and servomotor 12 includes a normally pressurized spring-loaded hydraulic relay 19. Should the turbine speed rise abnormally, the hydraulic pressure is removed from relay 19 causing its piston to descend abruptly and thereby cause rapid closing of control valve 10 to shut off the steam flow to the turbine. A hydraulic damper 20 absorbs impact loads in the linkage 18 during such emergency stopping. Control errors due to variations in the relative positions between the control valve body 11 and the servomotor 12 are compensated by a linkage 15, 16, 17. The transition from full-arc control to partial arc control can be carried out simultaneously for all the control valves 10 or successively one after the other.