Patent GB-842381-A (GB)
Title: Improvements in speed governing systems for turbines
Inventor: CHILMAN JOHN ALFRED
IPC: F01D17/26
Filed: 1955-05-31
Abstract: 842,381. Turbines. ROTOL Ltd. May 29, 1956 [May 31, 1955], No. 15626/55. Class 110(3). [Also in Group XXIX] In a turbine speed governor of the kind in which the turbine throttle is adjusted by a double-acting hydraulic servomotor under the control of a valve member responsive to changes in turbine speed whereby the operation of the throttle tends to restore the turbine to its initial speed, and in which the valve member has a follow-up seating movable with the servomotor hydraulicallv actuated delayed action restoring means are provided for restoring the follow-up seating to its datum position, and the application of hydraulic fluid to such means is controlled by the follow-up seating itself acting as a valve. In Fig. 3, the servomotor comprises a sleeve 111 within which slides a piston valve 102 operated by flyweights 101 from the turbine and having three lands 103, 104, 105. The sleeve 111 is integral with a piston 113 and has a further piston 114 slidable on its lower end. The piston 114 has a ported sleeve 116 connected at 21 through a linkage to the turbine throttle valve. Pressure fluid is admitted to the bore 112 through a port 107 and passes.via ports in the valve 102 to an annular channel 10. On displacement of the land 103 following a speed change, pressure fluid passes from the channel 110 to the top of the piston 113 or to the underside of the piston 114 and is simultaneously exhausted from the region not now supplied through exhaust port 120 or 121. The space between the pistons 113, 114 is connected via a restricted passage 122, with a port 124 opening into the bore 115. The port 124 is normally closed by a land 125 on the sleeve 111 but after the sleeve 111 follows up the movement of the valve 102 upon a speed change, the port 124 is connected either to the pressure port 107 or to the exhaust port 120 with the result the pressure fluid gradually enters or leaves the space between the pistons 113, 114 and the piston 114 falls or rises and so readjusts the turbine throttle valve. In Fig. 6, a turbine 244 driving an alternator A is controlled by the adjustment of pivoted vanes 243 through a linkage 242, 240, 237, 234 by a governor unit comprising a double-acting piston 230 controlled by a three-landed piston valve 213 movable against a spring 273 by flyweights 207 driven from the turbine shaft 212. The valve 213 slides in a ported sleeve 220 pivoted to a differential lever 249. The lever 249 is also pivoted to the piston rod 231 and at 262 to a second differential lever 259. The lever 259 has a fixed pivot 260 and also a pivotal connection 258 with the rod of a second piston 256. The latter operates in a bore 254 fed with hydraulic fluid through a port 255 from pump 252 driven in company with the governor weights. The port 255 also supplies a conduit 263 connected through a space 264 with a port 218 in the sleeve 220. A further space 265 connected to an exhaust conduit 266 is separated from the space 264 by a shoulder 270 which normally registers with a restricted passage 268 connected to the right-hand side of the piston 256 but permits some leakage past its edges. The sleeve 220 follows up the movement of the valve 213 following a speed change but in its new position the shoulder permits a greater leakage of fluid into or out of the space to the right-hand side of the piston 256. The piston 256 through the levers 259, 249 therefore gradually moves the sleeve 220 in the opposite direction to that in which it was originally moved by the piston 230. The sleeve 220 thus follows the governor valve 213 as it moves back to its original position under the control of the flyweights. The speed governor may be used in conjunction with means responsive to changes in the pressure ratio across the turbine blading to adjust the sensitivity of the speed governor to produce the optimum droop for the prevailing pressure ratio. This adjustment is in the sense to oppose changes in the time taken to restore a steady speed condition. In Fig. 1, a turbine T with a supply duct 1 controlled by a throttle valve 2 drives a three-phase alternator A through a shaft 4 having an angle drive 8 to a centrifugal governor G1 ; the latter as shown comprises a needle valve operated by centrifugal weights against a spring and controlling the supply of fluid from a constant pressure pipe 12 through a pipe 13 to a spring-loaded piston 15 connected through a differential lever 20, and a rod 30 to a slotted arm 31 on the shaft of the valve 2. The pipe 13 has a bleed to drain through a restriction 18. Speed changes are anticipated by a load-responsive device comprising a two-phase motor 24 having a spring- loaded arm 23 connected to one end of the lever 20. One winding 25 of the motor 24 is connected to a current transformer 26 in the output line 7 and the other phase winding 27 is connected across the other two output lines 5, 6. A change of load results in a re-setting of the datum speed of the governor G1. To restore the governor to the speed originally selected its loading spring is adjusted through an arm 10 by a double-acting piston 69 controlled by a governor G2 also driven from the shaft 4 and comprising spring- loaded centrifugal weights controlling a spool valve. The governor G2 acts with some delay due to restrictions 71 in one or both of the pipes 66, 67 to adjust the arm 10 and hence the datum of the governor G1 upon itself detecting any difference between the steady speed maintained by the governor Gland the preselected speed. The latter may itself be varied by providing variable datum means for the governor G2. A device 34 sensitive to the pressure ratio across the turbine T comprises a pair of pistons 37, 38 responsive to the pressure on opposite sides of the turbine and operative on a balance beam 41 the fulcrum 42 of which is adjustable by a double-acting piston 46. Opposite sides of the piston are connected to a source of fluid pressure through restrictions 50, 51 and fluid drains therefrom through jets 52, 53 differentially obstructed by the beam 41 which is therefore balanced in a position of the fulcrum 42 and of the piston 46 indicative of the prevailing pressure ratio. The piston 46 adjusts the position of the pivot 32 in the slotted arm 31 and hence adjusts the sensitivity of the speed governing system. The butterfly valve 2 may be replaced by a valve designed so that a linear relationship exists between the displacement of the valve operating member and the output torque of the turbine. The device 34 may be omitted and the arm 31 may have a fixed pivotal connection in some cases.