Patent GB-1338671-A (GB)
Title: Control devices for gas turbine power plants
IPC: F02K1/17
Filed: 1971-04-19
Abstract: 1338671 Jet nozzles; controlling gas turbine plant SOC NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION 19 April 1971 [4 Feb 1970] 20551/71 Headings F1G and F1J Control device for a gas turbine power plant of the type comprising a compressor, a combustion chamber supplied with air from the compressor and with fuel, a turbine supplied with combustion gases coming from the combustion chamber, and a nozzle for discharging the combustion gases coming from the turbine, said device comprising means for metering the fuel flow to the combustion chamber and means for varying the cross-sectional area of the nozzle, wherein the means for varying the cross-sectional area of the nozzle is controlled as a function of the fuel flow rate C delivered to the combustion chamber, the static air pressure Ps4 at the exit from the compressor, and the static gas pressure Ps7 at the turbine exit, so that at least under certain conditions of operation, an output quantity defined by the expression n which # disignates a constant co-efficient of reduction has a desired predetermined value. The output quantity constitutes an indirect but accurate indication of the temperature Tt5 of the combustion gases at the turbine intake and enables the cross-sectional area of the nozzle to be adjusted in relation to the rate of fuel flow to maintain the temperature of the gases at the turbine intake at an optimum value. The rate of fuel flow is controlled by a spool valve 30 fixed to a servopiston 32 and connected by a tension spring 39 to a system of levers L and 40 to capsules 33 and 34, the capsule 33 being evacuated and the capsule 34 being subject to the pressure Ps4 of the air delivered by the compressor. The fulcrum between the levers L and 40 is a roller 42 on a lever 43 pivoted to a lever 42 which is oscillated by a cam 47 on a shaft 48. The angular position of the shaft is therefore related to the pressure Ps4 and a pick-up 49 transmits a signal corresponding to the shaft position, to a computer E. The computer also receives a tachometer generated signal which is a function of the compressor speed N, compares this with a desired value for N, as determined by the position of a pilot operated handle 21 and transmits a correction signal to a motor 50 which rotates the shaft 48. The computer also receives a signal which is a function of the cross-sectional area S of the nozzle. This signal is generated by a device comprising a first capsule 80 subject to the pressure at the turbine exit, Ps7, a second capsule 81 subject to lower pressure #Ps4 obtained through a restrictor K, and a system of levers U, 86, 89 and 90, and cam 92 mounted on a shaft 93 which also carries a pick-up 94. The signal is a function of the value and is compared with a predetermined desired value. Correction is made by a motor M1 which moves the roller 88 and thus the fuel flow control valve 30, to achieve the desired value of # Ps4 - Ps7 and hence of the temperature Tt5 at the turbine intake, by adjusting the cross-sectional area of the nozzle. The adjustment is effected by a twostage hydraulic servosystem using fuel drawn from the high pressure supply line. Safety device If the computer E fails, then the pilot closes a switch 70a which opens a valve 70 and admits pressure fluid to a clutch 55. The position of the shaft 48 is then directly controlled by the position of the pilots handle 21, since the motor 50 drives through a torque-limited clutch 53 which is over-ridden by the solid connection through the clutch 55. The pilot then controls the fuel flow manually and the nozzle is maintained in its fully-open position.