Patent GB-968190-A (GB)
Title: Regulating device for thermal turbo-machines
IPC: F01D17/16
Filed: 1960-10-17
Abstract: 968,190. Fluid-pressure servomotor systems; automatic control of turbines. BROWN, BOVERI & CIE A. G. Oct. 17, 1960 [Oct. 20, 1959], No. 35541/60. Headings G3P and G3R. [Also in Division F1] In a regulating arrangement for a multi-stage compressor or turbine with adjustable starter or rotor blades, or both, means are provided for individually adjusting the pitch of each blade row in such a way that for each arbitrarily chosen pair of valves of two operating parameters, each blade row has a prescribed pitch which is unique to that pair of valves. Each row of guide blades 3, Fig. 1, of an axial-flow compressor is adjustable by means of a reversible electric motor 42 controlled by an electric servomechanism comprising an input potentiometer 28, an output potentiometer 34 driven by the motor, and a relay 38 energized by the potential difference between the sliders of the two potentiometers and controlling the current supply to the motor. Each input potentiometer 28 is controlled by a three-dimensional cam 5, the cams being mounted on a shaft 4 which can be moved axially by means of a hand-wheel 8 or turned by a hydraulic servomotor 21. An oil pump 16 pumps oil from a tank 17 and returns it to the tank through a restriction 19 and a throttle 13, the pressure developed at the junction of the restriction and throttle being applied to the servomotor 21. The throttle 13 is controlled by a diaphragm 12 exposed on opposite sides to the intake and discharge pressures of the compressor. The cams 5 are shaped in axial sections for constant pressure difference between the intake and discharge of the compressor and are shaped in sections transverse to the axis for constant volumetric flow, so that the hand wheel 8 sets the volumetric flow to the desired value while the servomotor 21 controls the pressure difference. The shaping of the axial and transverse sections of the cams may be interchanged so that the hand wheel 8 sets the pressure difference to a desired value while the servomotor 21 controls the volumetric flow. In a modification, the motors 42 and their associated electric servo-mechanisms are omitted and the cams are linked to the guide blades by mechanical means comprising, for each cam, a toothed ring encircling the compressor casing and meshing with a gear-wheel on each blade pivot, the toothed ring carrying a pair of cam followers which engage the cam at diametrically opposite points. In a further modification, Fig. 8, the cams also are eliminated. A toothed ring 51 encircling the compressor casing and meshing with the gear-wheels 46 on the blade pivots has further teeth meshing with a toothed sector 52 rigidly connected to a planetary carrier 53 carrying a planet gear 54. The planet gear 54 meshes with a sun gear 56 fixed to a shaft 55 and also meshes with internal teeth on a wheel 59 loose on the shaft 55. The external teeth of the wheel 59 mesh with a pinion 58 fixed to a shaft 57. Shaft 57 is curned by the hand wheel while shaft 55 is turned by the hydraulic servomotor. With this arrangement, the control is accurate at three operating points only on the pressure-volume diagram of the compressor and is only approximately correct at other operating points. In all the above embodiments, both controls may be by hand or both may be automatic. When one of the control factors has to vary according to a prescribed programme, e.g., the volumetric flow for converter operation in a steelworks, the hand wheel can be replaced by a programme regulator. Two or more blade rows may be adjusted by a common cam or planetary gear. Adjustable rotor blades may be provided in addition to or instead of the adjustable guide blades. Temperature gradient may be used as a control factor, instead of the pressure gradient. The invention may be applied to the blades of the useful power turbine of a gas turbine plant, the hand wheel being replaced by an automatic regulator responsive to volumetric flow.