Patent GB-892987-A (GB)
Title: Gas turbine control system
IPC: F02C9/28
Filed: 1958-05-20
Abstract: 892,987. Gas turbine plant. GARRETT CORPORATION. May 20, 1958 [May 20, 1957], No. 16195/58. Class 110 (3). [Also in Group XXIX] A gas turbine control system comprises a combustion chamber and a rotor supplied with combustion products from the combustion chamber through a flow control device controlled in accordance with rotor speed, a metering valve which meters the fuel supplied to the combustion chamber, main control means for influencing the position of the metering valve in accordance with the temperature at a point in the flow path, and transition control means for influencing the position of the metering valve in accordance with speed changes of the rotor, the transition control means being arranged so that the influence on the metering valve of the transition control means produced by any speed change progressively decays. A gas turbine 7 is supplied with compressed air through a pressure-regulating valve 16. Fuel is supplied to the combustion chamber nozzle 20 from an engine-driven pump 66 through pipe 64 via a supply passage 62 in a fuel metering device 17 which includes a diaphragm-actuated fuel by-pass valve 59 controlling the return of fuel from supply passage 62. Valve 59 is responsive to air pressure in a diaphragm chamber 41, the controlling air for this chamber being taken from the turbine through pipe 34 and filter 33 and passing thence, via passage 32, a pressure-regulating valve 28 and restriction 30, into a pipe 24. This pipe communicates with a first of two series-connected control valves 23, 37 which are controlled by temperature-sensitive elements 22, 38 disposed in the turbine inlet and exhaust respectively. Control valves 23, 37 are fully open when cold; the second control valve 37 is connected through pipe 40 to the diaphragm chamber 41 which is bled to atmosphere through a fixed orifice 46. The fuel by-pass valve 59 is also controlled differentially by the pressures in two diaphragm chambers 70, 53 which are connected through reset conduits 18, 19 with opposite sides of a dashpot piston 75 in a servomechanism 10, this dashpot being supplied with pressure air from the regulating valve 28 through pipe 76 and two capillaries 77, 78 in parallel. Dashpot piston 75 is actuated by a servo-piston 98 which also actuates a variable area inlet nozzle ling 12 of the turbine, the servo-piston being hydraulically operated through a relay piston valve 84 controlling service ports 93, 94 to this piston and receiving oil pressure from an engine-driven oil pump 89a. The relay valve,84 is responsive to air pressure in a diaphragm chamber 82, this air being received from the regulating valve 28 through a restrictor 80 and having its pressure controlled by venting through a pneumatic speed sensor 9 which is driven from the turbine output shaft. On starting the turbine, a switch 29a in an electric circuit is moved to open the turbine air inlet pressure-regulating valve 16 through a solenoid pilot valve 16a and simultaneously to open a solenoid valve 29 which bleeds off air upstream of the open temperature control valves 23, 27 to atmosphere through an orifice 31, thus controlling the pressure in diaphragm chamber 41 until the temperature control becomes effective. Switch 29a is then moved to close the bleed valve 29. At relatively steady operating speeds an over-temperature condition at either the inlet or outlet of the turbine tends to reduce the control pressure in diaphragm chamber 41 and cause opening of the fuel by-pass valve 59 thus reducing the pressure of fuel to the burner. During transient speed changes corresponding to load changes, speed sensor 9 modulates the pressure in conduits 79 and diaphragm chamber 82 to increase this pressure on falling speed and vice versa. Thus on a load application and fall of speed, relay valve 84 moves upwardly to connect the lower side of servo-piston 98 to oil pressure so that this piston moves upwardly and opens the variable area inlet nozzle ring 12. Dashpot piston 75 also moves upwardly and unbalances the pressures on opposite sides thereof which pressures are applied to diaphragm chambers 53, 70, respectively. This causes closure of the fuel by-pass valve 59 and increased pressure to the burner 20. During this transistion phase the temperature control is ineffective owing to its time lag. The unbalanced pressures on opposite sides of dashpot piston 75 are fed back through passages 109, 111 to diaphragm chambers 108, 110 of the relay valve 84 in order to prevent an overshoot in the action of this valve. Following a corrective action of the servo-mechanism 10 by the speed sensor the relay valve 84 returns to its neutral position closing the service ports 93, 94, by equalization of pressure through a restricted passage 107 connecting diaphragm chamber 82 with an upper diaphragm chamber, the unbalanced pressures on opposite side of dashpot piston 75 being also gradually equalized through the capillaries 77, 78. The system also includes a flame-out safety device 117 comprising a diaphragm-actuated electric switch 118 in circuit with the solenoid pilot valve 16a to cause closure of the regulating valve 16 on flame failure, this switch being normally held open by a spring and being closed by a rise of pressure downstream of the temperature-control valves 23, 37, applied through a capillary 126. A speed-responsive switch 119 in the circuit ensures that this safety device is only effective after the turbine has attained an operating speed which is substantially above the flame-out speed. A further safety device 114 which is responsive to a low pressure in the combustion chamber inlet plenum 35 to cause closure of the air inlet valve 16, comprises another diaphragm actuated switch 115 in the same circuit which is normally held open against a spring by pressure from the plenum received through the pipe 34 and a further capillary. Specifications 760,656 and 892,988 are referred to.