Steam enters the turbine from the boilers into a series of valves. These valves are controlled by the governor with regulates the amount of steam passing through the turbine in order to maintain the constant speed required to generate power at 60 cycles per second.
A turbine is a series of fixed and rotating blades that extract the mechanical and thermal energy from the steam. The steam at 900psi and 900°F enters the small end of the turbine and expands through to the larger blades until the steam exits the turbine at 100°F in a near-perfect vacuum with 90% of energy extracted.
The generator is a large coil of copper wire that has a direct current magnet spinning at 3600 rpm in its center. Moving any conductor through a magnetic field produces an electric current. In the BPU generators, the conductors (copper wires) are stationary and the magnetic field rotates past them.
The field exciter supplies direct current power to the electromagnet to produce the magnetic field within the generator. By adjusting the voltage supplied, the exciter controls the alternating current voltage output by the generator.
The turning gear is used when the turbine generator is NOT on line (not running). Its purpose is to turn the magnet and the turbine at a slow speed to prevent warping.