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In February 1994, a GE steam turbine at South Carolina Electric & Gas Co.'s (SCE&G) Wateree Station was retrofitted with a state-of-the-art GE control system. This turnkey project was undertaken by GE Power Systems on a 23-year old Mark I turbine control system on Wateree Station's Unit 2, a 370-MW steam turbine with a once-through, supercritical steam supply. The retrofit has improved the steam turbine's reliability and availability and marks the first application of GE's SPEEDTRONIC Mark V system on a large, reheat steam turbine.
Wateree Station is located on the Wateree River near the town of Eastover, S.C., approximately 30 miles southeast of Columbia. The coal-fired power station produces 740 MW of electricity and is the second largest generating station on the SCE&G system. Unit 1 was completed in 1970 and Unit 2 in 1971.
Each unit has a Riley Stoker boiler rated for 2,567,000 pounds/hour (lbs/hr) primary steam flow and 2,059,000 lbs/hr reheat steam flow. The operating temperature is 1,005 F at both superheater and reheater outlet, and the operating pressure at the superheater outlet is 3,550 psig.
Project background
In June 1992, SCE&G's Technical Services group conducted a feasibility study to determine whether it should rebuild the two units' Mark I Electro-Hydraulic Control (EHC) systems or install new ones.
The study recommended the Mark I EHC and turbine supervisory instrumentation (TSI) systems be retrofitted on Unit 2 first, primarily because of that unit's poor reliability and throttle pressure control. The findings from SCE&G's study are highlighted in Table 1. The project commenced during a planned major maintenance outage which began Feb. 6, 1994, and ended April 3, 1994. Table 2 presents the scope of Unit 2's retrofit.
Mark V overview
The Mark V is a triple modular redundant (TMR) system providing fault-tolerant turbine control via triple redundant hardware and software voting (Figure 1). The system applies turbine control techniques learned and refined over 40 years and incorporates hardware and software made available by modern electronic technology.
The retrofitted turbine control system includes microprocessor-based controllers, redundant process sensors and two-out-of-three hardware voting on critical control...