Double Automatic Extraction Turbines Gain New Life with Digital Controls, 1993 Engineering Conference Proceedings

John W. Mitchell

C. Scott Harclerode

Many two and three-valve steam turbines are operating base loaded in power plants with one or both extraction valves blocked. Turbine-generators of this type were installed widely in pulp and paper mill utilities during the 1940’s, 50’s and 60’s to efficiently produce steam at several different pressures. Complicated three-arm linkages used on extraction turbines are notoriously difficult to keep in proper adjustment so extraction header pressures must often be controlled by using far less efficient pressure reducing valves or PRV’s. Unfortunately,

few of today’s turbine technicians understand multi-valve mechanical-hydraulic governors.

This paper discusses how digital control systems are being used to recapture design efficiencies. The double automatic extraction condensing turbine (DAEC) control retrofit performed 3 years ago at the Groton, Connecticut Naval Submarine Base power plant is described.

The heart these new digital systems is the imbedded three-valve algorithm(TVA) software that is described in this paper. An example is given which illuminates subtle aspects of turbine operation that surface when valve and generator limits are reached or priorities are changed.