The application required large electrical load changes with very limited variations in frequency and voltage. With a dual-shaft gas turbine, nominal rating 8000 kilowatts, instantaneous loads up to 90 per cent rated were successfully accepted and rejected with frequency maintained within a one and one half per cent band. Voltage variation did not exceed four per cent. Frequency and voltage recovery were well within two seconds. The foregoing was accomplished by incorporating a control system which permitted operation of the turbine at other than normal operating conditions when auxiliary control valves were preset in anticipation of the load variation. The auxiliary control valves were air-inlet throttling valves, an inter-turbine bleed valve, and an additional fuel valve. The basic machine consisted of a 15-stage axial compressor, a two-stage, high-pressure turbine, and a two-stage power turbine. The unique requirements necessitated off-design operation and considerable extrapolation from known test data. However, it was possible to program the control-system components so that a conventional pneumatic control system was capable of maintaining speed within the prescribed band even though the applied load varied from that anticipated by as much as 12.5 per cent.

As worldwide power requirements increase, power generation facilities must begin to think more closely about the reliability of existing units. In order to enhance plant capability, many power producers are considering control upgrades to aging equipment as an alternative to adding new machinery. This paper details an advanced digital control system coupled with a progressive valving scheme and a unique man-machine interface that features the following: (1) increased unit reliability due to the replacement of the pneumatic control system with a state-of-the-art, digital controller and an electro-hydraulic fuel valve, (2) cooler, more predictable start-ups achieved by removing the relay sequencer and substituting an advanced software-driven sequencer, (3) an intuitive, color graphics operator control station that offers trending, archiving, and rapid configuration. The scope of this paper will describe this system as it applies to a Westinghouse 191G gas turbine. This unit is located at a peaking facility in Astoria, New York. The control retrofit was successfully completed in June 1991.

In recent years, civil aircraft projects are showing a continuous increase in the demand of onboard electrical power, both for the partial substitution of hydraulic or pneumatic controls and drives with electrical ones, and for the consumption of new auxiliary systems developed in response to flight safety and environmental control issues. Aiming to generate on-board power with low emissions and better efficiency, several manufacturers and research groups are considering the possibility to produce a relevant fraction of the electrical power required by the aircraft by a fuel cell system. The first step would be to replace the conventional auxiliary power unit (APU, based on a small gas turbine) with a Polymer Membrane fuel cell type (PEM), which today is favored with respect to other fuel cell types thanks to its higher power density and faster start-up. The PEM fuel cell can be fed with an hydrogen rich gas coming from a fuel reformer, operating with the same jet fuel used by the aircraft, or relying on a dedicated hydrogen storage onboard. The cell requires also an air compression unit, where the temperature, pressure and humidity of the air stream feeding the PEM unit during land and in-flight operation strongly influence the performance and the physical integrity of the fuel cell. In this work we consider different system architectures, where the air compression system may exploit an electrically driven compressor or a turbocharger unit. The compressor type and the system pressure level are optimized according to a fuel cell simulation model which calculates the cell voltage and efficiency as a function of temperature and pressure, calibrated over the performances of real PEM cell components. The system performances are discussed under different operating conditions, covering ground operation, intermediate and high altitude cruise conditions. The optimized configuration is selected, presenting energy balances and a complete thermodynamic analysis.