Patent GB-1374871-A (GB)
Title: Digital computer control system for monitoring and controlling operation of industrial gas turbine apparatus
IPC: F02C9/50
Filed: 1972-09-26
Abstract: 1374871 Automatic control systems WESTINGHOUSE ELECTRIC CORP 26 Sept 1972 [15 Oct 1971] 44327/72 Heading G3R A gas turbine is controlled in respect of its fuel and air supply by a digital computer in response to signals from a plurality of sensors of selected turbine parameters, including exhaust temperature, the air supply being continuously regulated by the position of air flow modulating means so as to maintain the exhuast temperature at a desired value. The Specification describes a system for automatic control of one or more gas turbine sets operable on gaseous or liquid fuel, or a combination of both, using a digital computer which is programmed to direct automatic start and run up and shut down, either normally or under "emergency" conditions, automatic or manual synchronization of the generator with the supply network, and to control the set either to maintain constant electrical power output by a retroactive loop or constant exhaust temperature, also retroactively, as selected by an operator. Some details of the computer operation are given and illustrated by flow and block diagrams but a fuller description is given in Specifications 1374809, 1374810. Auxiliary features such as alarms, print-outs, &c. are described. The system has the following features in particular;- Mode 1 - start-up. The computer produces an increasing speed reference voltage with which a voltage derived from pulses from a magnetic pickup on the turbine shaft are compared. The resulting error signal operates electro-pneumatic fuel and air flow controls, the latter comprising a set of radial guide vanes whose angles are adjusted by a rotatable ring; the arrangement for this is non-linear, the adjustment angle being a function of speed. The error signal is limited between upper and lower values to prevent flameout and other malfuntioning, and may be overridden by signals from vibration, pressure and temperature sensors, various areas of which are given different "weight" at different stages. An auxiliary speed sensor provides signals relevant to over speed limiting. Acceleration (i.e. rate of change of speed) is also limited.  Mode 2 - synchronization. This is effected when the speed reaches 106% of normal value. It is followed by automatic and gradual application of electrical load to the generator. The air flow is regulated by the speed signal in this mode also. Mode 3 - constant electrical load. The fuel is controlled by the difference between actual and desired K.W. loading using a proportional plus integral system, the air flow still being controlled in response to speed. Mode 4 - constant exhaust temperature. This may be selected instead of mode 3 when the exhaust is within 50‹F of normal and synchronization and loading is completed. In this mode the air flow guide vanes are adjusted in response to a stored profile of combuster shell pressure versus exhaust temperature. Account is also taken of "average blade path temperature" in a system having a dead band and an integral term. The computer samples the various systems periodically and the outputs of thermocouples for the temperature measurements, and the computer itself, are periodically automatically checked.