finding the overall system efficiency
$$Eff = \frac{P_{out}(overall \; system)}{P_{in}(overall \; system)} 
      = \frac{V \times A}{W} $$

The result is always &lt; 1 due to losses. The numerator of your equation is NOT the sum of power generated(calculated from voltage and current values) plus mechanical power from the turbine. The generator converts mechanical power to electrical power (think of it as a large transducer which is a device that converts one form of energy into another form). \$P_{gen} = P_{turbine} - energy \; losses\$ translating mechanical to electrical power. Don't add \$P_{gen} + P_{turbine}\$ in the numerator.

Stepping through the process:


Heat is generated to boil the water by means of an electrical supply \$(P_{in} = W)\$. Heat input is regulated via a varistat. Not all heat can be used to raise the temperature of the water (some is lost to the environment because the boiler’s insulation is not perfect). This step has \$Eff_1\$ (&lt;1)
Water heats up and produces steam. The steam's pressure and temperature can be measured with \$P\$ and \$T\$. Steam exits the nozzle which drives the turbine wheel. Not all heat energy from the steam acts on the turbine because some steam escapes and not all the steam's heat energy can be converted into mechanical work (thermodynamic limitations prevent this). This step has \$Eff_2\$ (&lt;1).
The turbine's mechanical power (shaft angular speed x torque) is converted into electrical power by the generator. Due to system losses (bearing friction, generator windage, eddy currents, \$I^2 \times R\$ heat losses, etc), not all mechanical power can be converted to electrical power. This step has \$Eff_3\$ (&lt;1).


Overall efficiency = \$ Eff_1 \times Eff_2 \times Eff_3 \$ = efficiency equation above.