Impact of existing fault protections of wind power plants with Doubly Fed Induction Machines on Fault Currents

Abstract

With constant increase in the number of wind power plants and thus their penetration in power production, system robustness and stability have become of a high interest. Due to their advantages, doubly fed inductions machines are mainly in use as generating units in wind power plants. While rotor windings are connected to the grid over power converters, stator windings are directly connected to the grid and thus these generating units are highly sensitive to voltage disturbances. Voltage drops during faults lead to high voltages and currents on rotor side due electromagnetic coupling between stator and rotor. These voltages and currents can damage expensive power electronics on the rotor side. In the past, to save the equipment, wind power plants with doubly fed induction machines have been disconnected from the grid during faults which is unacceptable today when the high number of these plants is considered. Grid operators require from these types of power sources to have fault ride through or low voltage ride through capabilities to support the grid during low voltage periods. This paper presents an overview of the currently existing techniques developed to enable fault ride through requirements for doubly fed induction machines, and consequently their influence on modeling these power plants for fault calculation and relay protection purposes.