Patent GB-597337-A (GB)
Title: Improvements in or relating to gas turbine power plants
Filed: 1945-05-17
Abstract: 597,337. Fluid-pressure servomotor systems. SULZER FRERES SOC. ANON. May 17, 1945, No. 12394. Convention date, May 19, 1944. [Class 135] [Also in Group XXVI] In a gas turbine plant of the type in which the working medium flows in a circuit containing a compressor and a turbine driving this compressor and in which working medium is extracted from the circuit to drive another turbine producing useful output and fresh working medium is introduced to make up for that withdrawn, the distribution of the working medium between the two turbines is controlled by a regulating device which operates a valve in a pipe byepassing at least one stage, but not more than one-third of the stages of the turbine driving the compressor so that this valve is opened when the useful output of the plant is increased. In a gas turbine plant, Fig. 1, the working fluid flows around a circuit formed by low- and high-pressure compressors 1, 3, a heat exchanger 5, a heater 11 and a compressor driving turbine 13. Some of the working fluid is taken from the circuit at point 8 and used as combustion air for the burner 19 in the combustion chamber 10, the gases from which pass through the heater 11 to the useful output turbine 22. The amount of working fluid taken from the circuit and thus the amount flowing to the two turbines 13 and 22 is controlled by a valve 30 in a pipe 29 byepassing at least one stage of the turbine 22. The setting of the valve 30 is adjusted by a regulating device 34 which is influenced by the compressor driving turbine governor 35, the pressure in the inlet pipe 12 to the compressor driving turbine 13 and a load-setting lever 36. When running under steady conditions, the plant is controlled solely by the governor 35 and the pressure in the pipe 12 acting through the regulating device 34 and servomotor 31 on the valve 30. When the output of the plant is increased by movement of the lever 36, the regulating device 34 first starts to close the valve 30 and if when this valve is fully closed, additional power is still required, the device 34 begins to open the valve 38 in the pipe 37, byepassing at least one stage of the compressor turbine 13 so as to increase the speed of this turbine and the pressure and output of the compressors 1, 3. If, when the valve 38 is fully open, still further power is required, the device 34 then supplies current to the motor 28. When the output of the plant is decreased by movement of the lever 36, the valve 30 is first fully opened by the device 34 and if this is insufficient temporarily operates the blow-off valve 45. A regulating-device which enables these operations to be effected is shown in Fig. 2. The governor 35 and bellows 50 responsive to the pressure in the pipe 12 are connected to the opposite ends of a lever 52 attached to the middle of which is a lever 63 to which is attached in turn the piston 71 of a servomotor. Any change in the compressor speed or the pressure in the pipe 12 will cause pressure oil to be supplied to the cylinder 75 and move the piston 76 to stress the spring 78. This spring will move the control valve 79 and allow pressure oil to flow into or be discharged from the pipe-line 32 which will in turn open to close the valve 30. The control valve 79 will remain open until the pressure in the cylinder 75 balances the stress in the spring when it will automatically close. The regulating range of the valve 30 is so chosen that under steady running conditions no further control of the plant is necessary. When the load on the plant is increased by movement of the lever 36, the roller 58 is pressed downwards by the cam 57 and compresses the spring 61, the action of which is damped by a dashpot 68. This spring forces the lever 63 downwards and this actuates the piston 71 of the servomotor and allows pressure oil to flow to the lower side of the piston 76 and so tension the spring 78. As before, this spring lifts the control valve 79 to and allows pressure oil to be supplied from the pipe 80 to the pipe 32 to operate valve 30. As the pressure in the pipe-line 32 is balanced against the stress in the spring 78, the larger the amount of movement of the piston 76 the higher is the pressure in the line 32. For a large change in load, the pressure in the line 32 will be high enough to fully close the valve 30 and to operate the servomotor 39 so as to open the valve 37 in the byepass of the first stage of the compressor turbine. A still further increase in pressure in the line 32 will operate the servomotor 87 actuating the switch arm 91 which brings the auxiliary motor 28 into operation. When the load is reduced by operation of the lever 36, the roller 94 is pushed downwards and the spring 96 given a compression stress which moves the control valve 97 downwards and allows pressure oil to flow out of the cylinder 47 to the drain pipe 99. The valve 45 is then opened by the spring 101 and the pressure in the pipe 12 falls, which in turn causes a shortening of the capsule 51 and the control valve 97 raised so that pressure fluid is supplied to the cylinder 47 from the pipe 98 and the valve 45 closed again. The normal pressure in the pipe 12 depends on the position of the cam plate 93 which is dependent, upon the setting of the lever 36 which corresponds to the load on the plant. Any increases in pre-set pressure will lengthen the capsule 51 and open the control valve 97 and allow air to blow off through the valve 45. A drop in pressure in the system will also operate the control valve 79 through the capsule 50 and lower the pressure in the pipe system 32, 33, 85 and open the valve 30, close the valve 37 and switch out the motor 28.