GB605093A - Improvements relating to temperature indicating and control systems - Google Patents

Abstract

605,093. Automatic control systems for gas turbines. POWER JETS (RESEARCH & DEVELOPMENT), Ltd., and ALCOCK, J. F. Dec. 13; 1945, Nos. 33834/45 and 32274/46. [Classes 35 and 38 (iv)] In a gas turbine temperature-control system, as the temperature of a thermosensitive ferromagnetic element passes through the Curie point the consequent alteration in magnetic flux causes the operation of devices regulating the supply of heat to the zone adjacent to the element. In the embodiment shown, the thermosensitive element 1 and armature 3 are in parallel across the permanent magnet 8, the circuit being completed by soft-iron bars 7. The armature 3 is pivoted so as to be attracted by poles 7a and is normally urged by spring 4, its, present air-gaps at each end and to close the open end 5 of pipe 9 with the disc 6. The duct 26 supplies the chambers 22, 23 with air from the compressor delivery, the pressure in chamber 23 being maintained at a constant value relative to the supply by the vents 28, 29 communicating with the atmosphere, and subject to a maximum set by relief valve 30. Chambers 22, 23 are separated by diaphragm 11, fitted with flexible portion 51 and supporting rod 32, of piston valve 33. At starting, the compressor pressure is negligible, the control is inoperative and the light biassing spring 36 maintains valve 33 in the full fuel supply position. At speed, with the element 1 at or above the Curie point, the reluctance of the element is raised above the value at normal temperature and the flux density in armature 3 is correspondingly increased, resulting in its rotation towards the pole pieces 7a, thereby opening pipe 9 to the atmosphere and lowering the air pressure in space 22. The pressure in space 23 thereupon operates to depress the diaphragm 11 and to close the fuel valve 33. Cut-off at acceleration is prevented by arranging to provide element 1 with an adequate thermal lag, armature 3 may be balanced against gravity forces and a suitable force-distance characteristic is produced by the shaping of poles 7a. To prevent local over-heating, a number of units may be provided in the duct, all connected to the pipe 9. In a further embodiment (not shown), the fuel supply piston valve is operated by an armature controlled by two opposed A.C. energized solenoids, in series with one of which is a choke coil the impedance of which is varied by a thermosensitive magnetic element. This system may be rendered inoperative at low speeds and may have a modified temperature response, e.g. to permit an increase in temperature with a reduction of engine speed. A wheatstone bridge circuit and thermionic amplification may be incorporated. The invention may also be applied to the control of temperature in gas-turbine heat exchanges employing the exhaust gases as the heating agency. In one form of construction (not shown) the armature is pivoted on ballbearings and two sealing plates are provided between the sensitive element and the magnet which protect the latter from both hot gases and radiant heat.