Patent GB-289026-A (GB)
Title: Improvements in and relating to turbine regulating systems
IPC: F01D17/00
Filed: 1928-04-17
Abstract: 289,026. British Thomson-Houston Co., Ltd., (Assignees of Standerwick, R. G.). April 20, 1927, [Convention date]. Dynamos, regulating. - Relates to the regulation of a steam turbine which runs at fixed speed owing to the alternating current generator which it drives being connected to main bus bars supplied by other alternating-current machines which are controlled to fix the frequency of the system. The turbine is governed so that, although it will take all the steam that is available up to full capacity, a device operates to prevent the generator driven by it from being overloaded. The governing is effected by relay apparatus responsive, for instance, to the pressure in the header of a waste-heat boiler system, or, in the case of a back-pressure turbine, to the pressure in the exhaust. A speed-responsive pre-emergency governor is also provided, but it is normally inoperative, and takes over the control of the turbine only when, for instance, the load is taken off by opening the circuit of the generator. Fig. 1 shows the application to an extraction turbine 1 which may be arranged as described in Specification 7697/13, [Class 110 (iii), Turbines &c.], with a controlled extraction conduit 4. The turbine drives an alternating-current generator 22 the leads 23 of which are connected to the main bus bars 24 of a system supplied by other generators through leads 25. Steam is supplied from the header 78 of waste-heat boilers 77. The main valve 10 is actuated by an oil servo-motor 21 through gearing 17 and cam 15. The servo-motor is controlled by pilot valves 46, 48. The stem 39 of the pilot valve 46 is connected to a centrifugal governor 36 and preferably rotates with it. The adjustable bushing 42, the movement of which is limited by steps 56<c>, is controlled by a synchronizing arrangement, such as that described in Specification 265,398, comprising a synchronizing motor 56 geared to a nut 53 by which the length of the bushing-rod 50 is adjusted. A lever 51 connects the rod 50 to a follow-up linkage 57, 58, and to a floating lever 59 which is also con. nected to the stem 60 of the pilot valve 48. A link 68 connects the lever 59 to a lever 69 having a magnetic pivot 91 which is pulled over by a spring 94 in emergency when the coil 92 becomes de-energized. This pivot requires manual re-setting. The other end of the lever 69 is connected by a rod 70 to a device 72 rresponsive to the pressure in the header 78. Under normal conditions of working the speed-governor controlled pilot valve stem 39 is inoperative, and leaves open the passage through the pilot valve 46. The governing is effected by the pilot valve stem 60 under the influence of the steam pressure responsive device 72, the pressure in the header 78 remaining substantially constant, and the turbine utilizing all of the steam available. If the supply of steam increases to such an extent that the generator 22 tends to become overloaded, the winding 95 of the synchronizing motor 56 is energized, and the bushing 42 of the pilot valve 46 is shifted to reduce the steam admission to the turbine. The automatic device for energizing the winding 95 on overloading comprises an ammeter 83 in a circuit 88 connected with the output leads 23 by a transformer 89. The pointer 84 of the ammeter co-operates with contacts 85, 86. The. bushing 42 is restored when the load has decreased, and pressure has increased in the header 78 by a plate 81 on the rod 70 closing contacts 82, and so causing the other winding 96 of the motor 56 to be energized. The maximum load on the generator 22 may be fixed by adjusting a resistance 90 in the ammeter circuit 88. When either of the main circuit-breakers 26, 27 is opened, a plate 28 is moved off contacts 29, and breaks the circuit 103 which energizes the coil 92 of the magnetic pivot 91. The spring 94 then pulls up the lever 69 and moves the valve stem 60 to render the pilot valve 48 inoperative. The control of the. turbine is then taken over at a slightly higher speed by the pilot valve stem 39 actuated by the speed governor 36. The circuits of the synchronizing motor 56 and the magnetic pivot 91 are connected to an independent supply 99, and switches 97, 98 are provided to hold the pivot 91 and to control the motor 56 when starting up the turbine. The oil for the servo-motor system is supplied by the oil pump 31 of the turbine. In a modification in which the apparatus is applied to a back-pressure turbine, the pressure-responsive device 72 is connected to the turbine exhaust, and the arrangement of the pivot 91 and of the switches 84, 98 is modified.