| 摘要 |
1,130,788. Steam turbine plant; engine stopgear. GENERAL ELECTRIC CO. June 30, 1966 [July 1, 1965], No.29370/66. Headings F1K and F1T. [Also in Division G3] In a steam turbine plant comprising a speed governor 12 controlling a set of control valves 3, and an emergency overspeed trip 15 for closing a stop valve 2, means are provided for closing the stop-valve 2 at a trip-anticipator speed which is above the normal speed but below the speed setting of the overspeed trip. If the speed thereafter falls below the trip-anticipator speed without having first exceeded the overspeed trip setting, the stop-valve 2 is re-opened. Since the stop-valve 2 is closed in anticipation of the operation of the overspeed trip, the peak speed attained after any such operation is less than it would otherwise have been. The speed governor 12 operates the control valves 3 through a servomotor 20 and a relay 13. The servomotor 20 comprises a pilot valve 21 controlling a servopiston 27, the fulcrum 24 of the follow-up lever 23 being adjustable to set the desired load corresponding to the normal speed. The overspeed trip 15, shown as an offcentre bolt device, is arranged to actuate a pivotable trip finger 30 to release a spring-loaded dump valve 32 to release hydraulic pressure in a conduit 34, feeding a relay 16 holding the stopvalve 2 open, whereby the stop-valve closes until the trip has been reset manually. The tripanticipator comprises a pilot valve 36 operated in accordance with speed, by a governor which may, as shown, be the main speed governor 12. When the trip-anticipator speed is reached, the valve 36 releases the hydraulic pressure in a conduit 40 to cause a spring-loaded dump valve 37 to release the hydraulic pressure in a conduit 35 feeding the relay 16. The stop-valve 2 consequently closes. Provided the turbine speed does not thereafter reach a value at which the overspeed trip 15 is operated, the stop-valve 2 re-opens when the speed subsequently falls below the trip-anticipator speed. Instead of being constant, the trip-anticipator speed setting may decrease at loads above 85% of full load to reduce still further the peak speed attained upon loss of such loads. In this case, when the control valves 3 are opened beyond the opening corresponding to 85% of full load, the sleeve 39 of the pilot valve 36 is raised from its normal position by an extension 56 of the piston rod of servomotor piston 27, acting through an adjustment screw 57 and a lever 51, to reduce the trip-anticipator speed. A dashpot 58 holds the sleeve 39 in its elevated position for a few seconds after a sudden drop of the extension 56 caused by sudden loss of load, to give time for the reduced setting of the trip-anticipator speed to take effect. In the case of a multi-stage turbine, the intercept valve and the stop-valve at the inlet to the I.P. turbine are controlled jointly with the valves 3, and 2, as indicated at 29, and 34a, 35a. |
