Phase shifter (machine)

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Phase shifter with 125 MVA in a substation. The housing, which is filled with hydrogen for cooling, has not led out the shaft on the left or right

In electrical power engineering, a phase shifter is a special rotating electrical machine that can neither be used as a motor nor as a generator, as its design means that it does not have an external mechanical shaft .

The phase shifters, which are designed as synchronous motors with greater power, are used in meshed power supply networks such as interconnected networks for the targeted influencing and control of the power flows. Phase shifters are preferably installed in central substations , where there are no synchronous machines such as in power stations that can work as phase shifters if necessary and where other methods of load flow control such as phase shifting transformers or the flexible AC transmission system (FACTS) - for example for economic reasons - not be used.

General

A phase shifter is technically a synchronous machine of a larger design, apparent powers over 40  MVA are common. However, a phase shifter does not serve to deliver electrical power, but rather fulfills the function in the electrical network - controlled via its magnetic excitation - to provide a large amount of inductive or capacitive reactive power in the power grid. This is particularly necessary when generating units cannot provide any or only insufficient reactive power to control the load flows in interconnected grids.

Since a synchronous machine does not start reliably in motor operation, the phase shifters have an integrated starter in the housing, designed as a three-phase asynchronous machine . In addition, appropriate, remotely controllable excitation systems for synchronous machines are integrated to control the magnetic excitation . The phase shifter is operated with a generator voltage in the range from 10  kV to 26 kV, the connection to the network levels, which are usually operated with higher voltages, is carried out by means of a machine transformer .

Larger phase shifters are constructed similarly to turbo generators and also include the cooling equipment required for operation. Larger phase shifters are operated in a gas-tight housing which is filled with hydrogen gas. Compared to air, hydrogen gas has a very high specific heat capacity , which allows effective cooling, but also requires additional safety precautions during operation, since dangerous oxyhydrogen gas is produced when it escapes into air .

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