Patent GB-732459-A (GB)
Title: Improvements in and relating to regulators for variable nozzle gas turbine powerplants
IPC: F02C9/22
Filed: 1952-10-22
Abstract: 732,459. Gas turbine plant. GENERAL ELECTRIC CO. Oct. 22, 1952 [Oct. 24, 1951], No. 26526/52. Class 110 (3). [Also in Groups XXIX and XXXV] A gas turbine power plant comprising a compressor supplying air to a combustion chamber feeding a high pressure turbine driving the compressor and a mechanically independent low pressure useful power turbine arranged in series fiow with variable angle nozzle means between them has means responsive to the speed of the useful power turbine to vary the fuel supply and means responsive to an operating condition of the compressor such as its discharge pressure for adjusting the variable angle nozzles. The gas turbine shown comprises an axial flow compressor 1 supplying air to a combustion system 2 feeding a high pressure turbine rotor 3 which drives the. compressor and exhausts through a variable angle nozzle ring 5 to a low pressure useful power turbine rotor 4, The fuel supply to the combustion system 2 is controlled by a throttle valve 16 which is opened against the bias of the spring 16b by bellows 16a. The pressure in the bellows 16a is controlled by the regulator 17. A speed signal from the tachometer generator 10 is supplied to the solenoid 20 connected to a pilot valve 21. Variations of this signal cause movement of the piston 29 connected to a lever 30 which actuates another pilot valve 32 which controls the supply or withdrawal of control. oil to or from the cylinder 39. The pressure in the cylinder 39 is supplied through conduit 41 to the bellows 16a of the throttle valve 16. The arrangement is such that an increase in speed of the turbine rotor 4 reduces the fuel supply and vice versa. The control panel 17a is used to adjust the speed of the turbine 4 and may be preset manually or controlled automatically by other means such as the discharge of the pump 6 driven by the plant. The lever 30 may be actuated by other means such as 'temperature responsive bulb 4b to decrease the fuel supply in the event of excessive exhaust temperatures. The variable nozzles 5 are actuated by a control ring 5d actuated by an hydraulic motor 11 the supply of control oil to which is controlled by a regulator 18. The pilot valve 42 of the regulator is positioned by a solenoid 46 to which current is supplied by a tachometer generator 9 driven by the compressor turbine through a rheostat 52. A stabilizing coil 48 is arranged in parallel with the coil 46 and is fed with current through a nozzle adjusting rheostat 50 and a stabilizing rheostat 52. The movable contact of the rheostat 51 is positioned by the piston of the hydraulic motor 11. The movable contact 52a of the rheostat 52 is positioned by a pair of hydraulic pistons 57, 58 through a rack-andpinion gear. The supply of control oil to the hydraulic pistons 57, 58 is controlled by a pilot valve 59 which is actuated by a lever 66 spring-biased on to a cam 55. The primary control of the lever 66 is a bell-crank lever 68 having one arm pivoted to the lever 66 and the other arm to a second lever 71 which is pivoted to a fixed fulcrum at 72. The lever 68 is attached to a rod 76 which moves in response to changes of temperature in the exhaust of the turbine 4. An increase in this temperature actuates the pilot 59 in such a manner to increase the resistance in the circuit of the rheostat 52 which results in opening of the nozzle vanes 5. The compressor-turbine rotor then speeds up and the exhaust temperature is thereby reduced. The increased speed of the compressor also results in a higher voltage from the tacho-generator 9 and an increased pressure in the bellows 79. The bellows 79 cause the lever 71 to pivot clockwise and modify the action of the bell-crank 68. The nature of this modifying effect is determined by the characteristics of the bellows 79, spring 82 and the length of the lever arms between the pivots 70, 76a and 80. The design of these parts and the cam 55 is determined by the relationship between the exhaust temperature and compressor speed that is desired. The variable nozzles 5 may be arranged to be moved outside the normal control range into a position in which the efficiency of the rotor 4 is considerably reduced or even exerts a braking effect on the rotor. The movement of the nozzles into this position may be effected by a speed governor 83 which in response to an over-, speed, condition closes a switch 83a and energizes a solenoid valve 85 which dumps the operating fluid from the hydraulic motor 11. Failure of electric current in the control circuit will permit pilot valve 42 to rise and cause the nozzles 5 to open. The tachometer generators 9, 10 may be replaced by mechanical governors connected through linkage to the pilot valves 21, 42. In another modification the pivot 76a of the bell-crank 68 is positioned by electrical means by a thermopile in the exhaust of the turbine 4. In a further modification, the bellows 79 are replaced by a device responsive to the rotational speed of the compressor such as a tachometer generator or mechanical governor. Specifications 638,494, 680,209, 700,092, [Group XXXV], and 707,272 are referred to.