The first turbo-generators were water turbines which propelled electric generators. Engineer Charles Algernon Parsons demonstrated a DC steam-powered turbogenerator using a dynamo in 1887. and by 1901 had supplied the first large industrial AC turbogenerator of megawatt power to a plant in Eberfeld, Germany. Turbo generators were also used on steam locomotives as a power source for coach lighting and water pumps for heating systems.
Construction features
Unlike hydraulic turbines which usually operate at lower speeds, the efficiency of a steam turbine is higher at higher speeds and therefore a turbo generator is used for steam turbines. The rotor of a turbo generator is a non-salient pole type usually with two poles. The normal speed of a turbo generator is 1500 or 3000 rpm with four or two poles at 50 Hz. Salient rotors will be very noisy and with a lot of windage loss. The rotating parts of a turbo generator are subjected to high mechanical stresses because of the high operation speed. To make the rotor mechanically resistant in large turbo-alternators, the rotor is normally forged from solid steel and alloys like chromium-nickel-steel or chromium-nickel-molybdenum are used. The overhang of windings at the periphery will be secured by steel retaining rings. Heavy non-magnetic metal wedges on top of the slots hold the field windings against centrifugal forces. Hard composition insulating materials, like mica and asbestos, are normally used in the slots of rotor. These material can withstand high temperatures and high crushing forces. The stator of large turbo generators may be built of two or more parts while in smaller turbo-generators it is built up in one complete piece.
Hydrogen-cooled turbo generator
Based on the air-cooled turbo generator, gaseous hydrogen first went into service as the coolant in a hydrogen-cooled turbo generator in October 1937, at the Dayton Power & Light Co. in Dayton, Ohio. Hydrogen is used as the coolant in the rotor and sometimes the stator, allowing an increase in specific utilization and a 99.0% efficiency. Because of the high thermal conductivity, high specific heat and low density of hydrogen gas, this is the most common type in its field today. The hydrogen can be manufactured on-site by electrolysis. The generator is hermetically sealed to prevent escape of the hydrogen gas. The absence of oxygen in the atmosphere within significantly reduces the damage of the windings insulation by eventual corona discharges. The hydrogen gas is circulated within the rotor enclosure, and cooled by a gas-to-water heat exchanger.
