Define the steam turbine system. In this example, a powerhouse turbine takes in steam to drive an electric generator that produces 6 megawatts of electricity per hour. If you know generator efficiency, which is 86 percent in this case, you can calculate the instantaneous power output of the turbine in horsepower.
Calculate the generator power required by dividing the 6 megawatt electrical output by the 0.86 generator efficiency factor to yield 6.976 megawatts.
Divide the 6.976 megawatts by 0.746 kilowatts per horsepower. This yields 9,351 horsepower coming from the turbine.
Consider the same steam turbine generating 9,352 horsepower. Since each horsepower of output requires 2,545-BTU/hour to produce, and the steam turbine efficiency factor is 0.85, then it takes 28 million BTU/hour to produce 9,352 horsepower from the turbine and 6 megawatts of power from the generator. You can calculate the turbine's power output at any rate of BTU production. In this case the turbine is extracting 12.46 million BTU/hour of heat from the steam.
Multiply the 12.46 million BTU/hour by 0.85 to obtain the net heat being converted to horsepower in the turbine. This calculates to 10.59 million BTU/hour.
Divide the 10.59 million BTU/hour by 2,545 BTU/hour/horsepower to yield the turbine output of 4,161 horsepower.
Define the steam turbine fuel-use application. If the same steam turbine produces the 6 megawatts by burning No. 6 fuel oil in the boiler, you can calculate the amount of power the turbine produces by measuring the fuel use. In this case, the boiler burns 119 gallons of No. 6 oil/hour with a combustion efficiency factor of 0.85 to produce the unknown turbine output.
Multiply the 119 gallons/hour by 145,000 BTU/gallon to yield 17.26 million BTU/hour x 0.85 or 14.67 BTU actually produced in the boiler.
Multiply the 14.67 million BTU/hour x 0.7225 combined boiler and turbine efficiency factors (0.85 combustion x 0.85 turbine) and divide by 2,545 BTU/hour/horsepower to obtain steam turbine output power at 119-gallons per hour of 4,164 horsepower. This would yield 4,164 x 0.86 generator efficiency factor x 0.746 kilowatts/horsepower, or 2,671 megawatts of power produced.