Differential protection for stator ground faults in a full-converter wind turbine generator

Abstract

Consolidated schemes and philosophies have been developed for Wind Energy Conversion Systems (WECS) protection. Although various studies have addressed this topic, including the internal protection function, there is still room for improvement, for instance, concerning the use of differential logic under varying frequencies. An aggravating factor related to protection issues is the high penetration of electronic devices in recent topologies, which may result in different responses in the case of internal faults, depending on the control strategy. In this scenario, conventional protection may not work properly. Based on this and considering the increasing tendency towards using full-converter WECS, there is a need to standardize them as well as improve their protection schemes. Thus, this paper analyses the application of the differential function in order to detect internal faults in a full-converter wind turbine generator. A differential protection scheme based on Discrete Fourier Transform (DFT) using dynamic window was discussed in this paper. The main objective was to reduce the phasor estimation error caused by the stator frequency variation. A complete protection scheme was implemented and tested using fault simulations from a Real Time Digital Simulator (RTDS). Very promising results were obtained. Furthermore, it was demonstrated throughout the paper that the grounding configuration greatly influences the protection performance of such equipment.