In electricity supply and generation, low voltage ride through (LVRT), or fault ride through (FRT), is what an electric device, especially wind generator, may be required to be capable of when the voltage in the grid is temporarily reduced due to a fault or load change in the grid. The voltage may be reduced in one, two or all the three phases of the AC grid. The severity of the voltage dip is defined by the voltage level during the dip (may go down to zero) and the duration of the dip.
Depending on the application the device may, during and after the dip, be required to:
For generating units such as wind turbines and solar power stations, the required LVRT behaviour is defined in grid codes issued by the grid operator. Examples of the such grid codes are the German E.On grid code [2] and UK National Grid code [3]
For critical loads such as power supplies for computer centers and industrial processes the required LVRT performance is defined by the application. Often a special device called uninterruptible power supply (UPS) is used to provide power to the critical load during the voltage dip.
Testing of the devices with less than 16 Amp rated current is described in the standard IEC 61000-4-11 and for higher current devices in IEC 61000-4-34
For wind turbines the LVRT testing is described in the standard IEC 61400-21 (2nd edition August 2008) More detailled testing procedures are stated in the German guideline FGW TR3 (Rev.22).
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