Patent GB-585860-A (GB)
Title: Improvements in or relating to gas-turbine plants
Filed: 1944-12-21
Abstract: 585,860. Gas turbines. STRUB. R. Dec. 21, 1944, No. 25640. Convention date, Dec. 24, 1943. [Classes 110 (i) and 110 (iii)] [Also in Group XXIX] In a gas turbine plant of the type in which the working medium flows in a circuit from which some of the medium is continuously extracted and in its place a make-up quantity supplied, and in which there is at least one turbine operated by the working medium flowing in the circuit and at least one turbine operated by the medium extracted from the circuit, the output of the turbine operated by the extracted medium is varied by alteration of the speed of the turbine in the circuit. In the plant shown, Fig. 1, the output of the turbine 21 is controlled by varying the speed of the turbine 13 which may be preset by the control 34. An increase in the speed of this turbine increases the speed of the compressors 1, 3 and raises the pressure in the gas generator 10 which allows a greater pressure drop through the output turbine 21. When the speed of the turbine 13 has been pre-set it is maintained by the governor 28 controlling the valve 32 arranged in the pipe 33 bye-passing the first stage of the turbine 21. The valve 32 thus controls the amount of working medium extracted from the circuit. A governor 40, driven by the turbine 21, prevents overspeeding of that-turbine, by controlling a valve 41 in the inlet pipe 20 and a valve 37 in a pipe 35 bye-passing the whole of the turbine. When the speed of the turbine 21 exceeds a predetermined value, the governor 40 fully closes the valve 41 and opens the valve 37 by an amount which is controlled by the speed of the turbine 13. In order to prevent the compressors from surging during periods of very low load, bye-pass and throttle valves 47, 51 and 55 are provided and are opened in succession by the governor 28 as the load decreases. The fuel supply to the burner 19, is controlled both by the control 34 and the thermostat 63 in the supply pipe 12 to the circuit turbine 13. A regulating apparatus that may be employed in the plant is shown in Fig. 2. The sleeve 81 of the governor 28 driven by the shaft 74 of the turbine 13 is connected to the valve 32 by an isodromic device comprising a spring 77 and a dash-pot 76. This device can only come to rest when the lever 78 is in a position in which the control valve 75 is in a neutral position and the spring 77 unstressed, i.e., when the governor is at the speed pre-set by the hand control 34. Any deviation from this pre-set speed by the turbine 13 will cause the sleeve 81 of the governor 28 to alter the position of the control valve 75 of the servomotor 31 and allow pressure oil to be supplied to the upper or lower side of the piston 84 which moves the valve 32 through the linkwork 85, 86. More or less working medium then flows to the turbine 21 and the turbine 13 speeds up or slows down and the sleeve 81 and valve 75 return to their original positions. During controlling movements, the piston 84 and the piston 87 of the dashpot 76 are moved. This causes a pressure to be built on one side of the piston 87 and the outer casing of the dashpot 76 moves and stresses the spring 77. As oil leaks through the hole 88, this pressure difference decreases until there is no stress in the spring. The governor 40 of the turbine 21 is connected to a servomotor which, under normal conditions, allows pressure oil to flow from the supply pipe 92 through the pipe 93 to the upper side of the pistons 94, 95 controlling the valve 41 in the supply pipe 20 and the valve 37 in the pipe 35 which bye-passes the whole of the turbine 21. Normally, the valve 41 is fully open and the valve 37 fully shut. In the event of overspeeding of the turbine 21, its governor 40 moves the servomotor piston 91 which connects the pressure oil supply to the pipe 98 and opens the pipe 93 to drain. The pressure oil is then supplied to the lower sides of the pistons 94, 95 which move and fully close the valve 41 and open the valve 37. The amount by which the valve 37 is opened is limited' by a piston 99 the position of which is controlled by the governor 28 of the turbine 13 so that the amount of working fluid passing through the bye-pass 35 is equal to the amount previously flowing through the turbine 21. Operation of the governor 40, therefore, does not affect the speed of the turbine 13. In the event of trouble with the plant, the servomotor controlling the valves 37, 41 may be operated either by the governor 28 or the hand control 34 through the lever 78 and push rod 97. The governor 28 independently controls through the lever 100 the valve 102 controlling the leakoff from the servomotors 53, 48 and 56. The springs which load these servomotors are so chosen relatively to each other that as the pressure rises in the servomotors due to closing of the valve 102, first, the servomotor 48, then, the servomotor 53 and finally the servomotor 56 come into action. When the speed of the turbine 13 is raised or lowered by the hand control 34, the fuel supply to the burner 19 is at the same time increased or decreased by the valve 104 connected to the control through a linkwork 129, 130, 121, 122, and 106. The temperature of the working fluid supply to the turbine 13 is controlled by a thermostat 63 connected to the lever valve 104 through a servomotor 119. Any variation of the temperature causes the rod 63 to expand or contract and actuate the control valve 123 of the servomotor 119. This allows pressure oil to be supplied to the upper or lower side of the piston 125 which moves and actuates the fuel valve 134. Movement of the piston 125 moves the dash-pot 127, loads the spring 128 and returns the control valve 123 towards its neutral position. The loading of the spring causes the pressure to build up on one side of the dash-pot piston and a leak-off through the piston allows this pressure difference to decrease until the spring is unloaded. The dash-pot 127 and spring 128 allow the thermostat to control at a fixed temperature and prevent over-regulation. The length of travel of the fuel regulating valve is limited by the pressure in the gas heater 10. A pin 107 on the control rod 106 of the valve 104 engages a curved opening 108 in the plate 109. This plate is displaced in the directions indicated by the arrows 113 through the rod 110 and lever 111 by the spring loaded piston 112. This displacement can be effected by hand through the lever 114. The curves of the opening 108 are so chosen that a range of regulation is obtained which will not allow oscillations in the system. The turbine 21 may be used for driving the compressors and the turbine 13 may be employed for giving the useful power and the two turbines may be coupled together. An electric motor 27 serves as a starting motor and may be used as an auxiliary motor for equalising surplus or lacking power.