Turbine-electric transmission
A turbine-electric transmission system includes a turboshaft gas turbine connected to an electrical generator, creating electricity that powers electric traction motors. No clutch is required.
Turbine-electric transmissions are used to drive both Gas turbine locomotives and warships.
A handful of experimental locomotives from the 1930s and 1940s used gas turbines as prime movers. These turbines were based on stationary practice, with single large reverse-flow combustors, heat exchangers and using low-cost heavy oil bunker fuel. In the 1960s the idea re-emerged, using developments in light weight engines developed for helicopters and using lighter kerosene fuels. As these turbines were compact and lightweight, the vehicles were produced as railcars rather than separate locomotives.
Hybrid turbine-electric systems
The patented US 8432048 B1, hybrid engine, is a turbine-electric transmission system that can be used to power warships, airplanes, and power plants. The gas turbine engine includes a compressor, a combustor, and a turbine which are necessary to harness mechanical energy. Inside the gas turbine engine air is taken in and compressed in the cold section of the engine, and brought to a higher pressure. Fuel is then sprayed in the air and ignites it so the combustion generates a high-temperature flow. The heated, high-pressure gas enters a turbine, where it expands down to the exhaust pressure, producing a shaft work output in the process. The exhaust is fed into the power turbine used to power an output shaft for whatever desired application. The power turbine is also connected to the electric generator, which converts mechanical energy into electrical energy. The electric generator driven by the power turbine charges the battery needed in order to drive the motor that supplies compressed air into the combustor.During cruise speed the electric motor does not have to be functioning, only the gas turbine engine is required to continue running in order to supply the required hot gas flow to the power turbine through the manifold. However, during slower speeds the gas turbine engine is not operated and only the electric motor is required to drive the compressor to supply compressed air to the combustor. The only time that the turbine, combustor, and compressor are all required to be running is when maximum power is forced on the engine. During this time they all work together to create a hot gas flow that will feed into the manifold, which then in turn feeds into the power turbine. The electric generator is operated when the gas turbine engine is running and also when the motor's battery needs charging.
Aircraft gas turbine engine system
The aircraft gas turbine engine system, patent number 5,867,979, is a gas turbine engine that is mounted on an aircraft, which the system generates and utilizes electrical and other power. The gas engine turbine system’s core is made up of a compressor, a three shaft propulsive gas turbine engine, which has three electrical generators. Each generator is connected to one segment of the shaft, which is part of the engine. Then a propulsive fan is driven by the compressor and the generators. The engine including many independent shafts is connected to the turbine engine, which is connected to the compressor that is connected to the fan. Each of the shafts independently and directly is powered by an electrical generator.One of the generator's main operations is to create power to provide the main source of electrical power for the aircraft. The other two generators create electrical power for the engine and provide back-up power for the aircraft. The two of the electrical generators additionally functions as electric motors so to facilitate the power transfer between the engine shafts.
The engine is provided with an auxiliary shaft that can transmit power from one of the main shafts of the engine to a gearbox mounted on the engines external casing. The gearbox in turn drives various electrical generators and hydraulic pumps. A single electrical generator could be driven by the gearbox. During an event of failure from the generator, there would, be an interruption in the supply of electrical power to the engine and the aircraft. In a multiengine aircraft an interruption may be acceptable for a few moments but for an aircraft that is required to fly a long distance, it would be necessary for the gearbox to drive an addition electrical generator for back up reasons. Thus, duplication of electrical power generators leads to difficulties in positioning the gearbox and heavy modifications to the gearbox.
Naval applications
Gas and steam turbines are most efficient at thousands of revolutions per minute. This is a major drawback because of the need for heavy gears, which drive the engine into one single duty, propulsion. Electric motors provide numerous applications including use of accessories besides that of propulsion. Permanent magnets and even motor generator sets will soon be included into Naval fleets that will have a larger variety of applications.Warships require the ability to cruise efficiently for long distances and also to have high power for intermittent bursts of speed. For that reason they use combined power systems that use an efficient prime mover, such as a diesel engine or a small gas turbine, for cruising and large gas turbines for high speed. Most of these use mechanical combination of power, through gearboxes and clutches, with systems such as CODOG or COGAG. Where electric transmissions are used, this is referred to as integrated electric propulsion or IEP.
A guided missile destroyer—for example the Zumwalt-class—allows a gas driven turbine to run generators driven by the turbine itself. This generator can produce electricity to move the ship and also operate a variety of its instruments and accessories. A lot of these electricity-generating turbines are being produced to include integrated electrical propulsion. Integrated electrical propulsion is when the engine strictly runs off of electricity, without the use of any gasoline, diesel, or fuel for that matter. The electric engine is more efficient due to only being electric and not gasoline based. It allows for less pollution and provides electricity to the naval ships instruments and applications. A lot of these electricity-generating turbines are being produced to include integrated electrical propulsion. A good example of one of these systems is the COGAL system.
An alternative approach is to use COGES, Combined Gas-Electric and Steam, to improve overall efficiency. A gas turbine-electric primary transmission is used, with a heat-recovery boiler in the exhaust flow to generate steam and thus electricity via a secondary steam turbine. Electric driven propulsion allows for movement of the ship and provides power generation on-board of the ship. Heat lost by gas turbines is not practical because it is wasting energy as heat dissipates into the surroundings. The COGES system allows the heat to be captured and converted into steam for the generation of electricity. Unlike diesel and other heavy-fuel turbines, the COGES captures the left over heat and exhaust from the turbine and it reduces pollutants from escaping into the atmosphere. The COGES system allows for practical applications in cruise ships, for example the General Electric LM2500.