Patent GB-1213008-A (GB)
Title: Improvements relating to control apparatus for steam turbines
IPC: F01D19/02
Filed: 1967-12-14
Abstract: 1,213,008. Automatic speed & acceleration control. GENERAL ELECTRIC CO. Dec.14, 1967 [Jan.3, 1967], No.56867/67. Heading G3R. [Also in Divisions G1 and G4] A control system for a turbine 1, Fig.1, includes an arrangement such as a digital calculator 29, or a thermal image and analogue calculator, Fig. 5 (not shown) which produces from the outputs of speed and temperature transducers 8, 28 on the turbine 1, signals representing the stresses at the bore and the surface of the rotor, comparing these with allowable stresses and selecting at 36 the smaller of the resultant error signals from 35,42, to control the turbine. This error signal is applied to the terminals 44 of a multiple switch in the first position of which (as shown) the turbine is run up to speed from rest. A speed signal from 8 is converted at 10 from frequency to amplitude variation, and compared at 13 with a speed reference from 12 to give a first control signal 14, and is also fed to a differentiator 15 whose acceleration-dependant output signal is combined at 16 with the error signal fed from 44, through a gain adjuster 18, to give a second control signal. The smaller control signal is again selected by a low value gate 20 to control the fuel valve 3 in the turbine supply, whereby the speed signal 14 controls the final phase of run-up. When full speed is attained, load is applied to the generator 2, driven by the turbine, by closure of contacts 5 of the multiple switch which is now changed over. This causes a load rate of change signal to be produced, by applying the output of a load sensor 21 to a differentiator 24, and this load rate signal is sent to the summer 16 whose other input is still derived from the stress signal at 44 but through a different gain adjuster 26. The measured load signal 22 is also compared directly at 13 with a load reference from 23, and the smaller of the two outputs of the summers 13, 16 is again selected at 20 to control the turbine. The digital calculator 29 comprises an a/d converter 31 applying the temperature signal to: (a) a unit 32 which calculates the surface stress, i.e. that arising due to temperature at the periphery of the rotor, and (b) a unit 33 which calculates the temperature induced proportion of the bore stress, which is that existing near the centre of the rotor; and further comprises an a/d converter 41 which produces a signal proportional to the square of the speed, from 10 representing the proportion of the bore stress due to centrifugal forces. The bore stresses are added at 37 and compared with a maximum allowable bore stress calculated at 34 from the temperature signal; and the surface stress is compared at 340 with a reference level set at 330. The resulting error signals are applied through the predictors 35, 42 to a low value gate 36 which feeds the lowest error signal to a d/a converter 43 supplying the required stress signal to terminals 44. The units 32,33,34 operate according to given equations, and include storage, multiplying and shifting arrangements, Fig.4 (not shown).  The thermal image arrangement, Figs. 5,6, (not shown) comprises a body (61) representing the rotor in thermal characteristics and having a bore, end plates (62) of insulating material thereon, an annular duct (63) carrying heating fluid, and circuitry to maintain a given relationship between turbine rotor temperature and the body (61). Strain gauges (68,69) measure surface stress and temperature induced bore stress, and the speed dependant bore stress is electrically calculated from the speed in an analogue manner.