With the steam turbine supporting the generator. In order to achieve high efficiency, the steam turbine is generally made high speed, usually 3000 r / min (frequency 50 Hz) or 3600 r / min (frequency 60 Hz). Nuclear power plant in the steam turbine speed is low, but also in 1500 r / min or more. High-speed turbo-generator in order to reduce the centrifugal force generated by the mechanical stress and reduce wind wear, the rotor diameter is generally relatively small, the length is relatively large, that is, the use of slender rotor. Especially in the 3000 r / min high-capacity high-speed unit, due to the strength of the relationship between the material, the rotor diameter is strictly limited, generally not more than 1.2 meters. And the length of the rotor body is limited by the critical speed. When the body length reaches more than 6 times the diameter, the second critical speed of the rotor will be close to the motor running speed, the operation may occur in the larger vibration. So the size of large-scale high-speed turbine generator rotor is strictly limited. 10 million kilowatts of air-cooled motor rotor rotor size has reached the above limit size, to increase the motor capacity, only by increasing the motor to achieve the electromagnetic load. For this reason, the motor must be cooled. So 5 to 10 million kilowatts of turbo generators are used better cooling effect of hydrogen or water cooling technology. Since the 1970s, the maximum capacity of turbo-generators has reached 130 to 1.5 million kilowatts. Since 1986, in the high critical temperature superconducting materials research has made a major breakthrough. Superconducting technology is expected to be used in turbo-generators, which will produce a new leap in the development of turbo-generators.