Crowbar resistors are three-phase resistance banks which are connected to the rotor windings of the DFIG (Doubly-Feed Induction Generator) such as in a wind power generator.
They are used to prevent damage to the inverter circuits attached to the rotor side when a fault occurs in the grid. During faults in the grid, a DFIG power converter, which has a restricted over-current limit, needs special attention. If the rotor current or DC link voltage reaches the threshold value, crowbar resistors disconnect the converter. This prevents the generator from turning into a squirrel cage induction machine. By using crowbar resistors, the DFIG can stay connected to the grid and continue its operation.
The crowbar resistors should be high enough to limit the short circuit rotor current and low enough to avoid overly high voltage in the rotor circuit. Crowbar resistors should be designed with low inductance and capable of handling very high currents for short periods.