Abstract
With the rapid development of wind energy, relay protection for large-scale wind farms has been attracting some researchers, due to the absence of standards. Based on the large-scale doubly fed induction generator (DFIG)-based wind farms located in Gansu Province, China, this paper studies the differential protection for the outgoing power transformer of large-scale DFIG-based wind farms. According to the equivalent circuit of the power grid integrated with wind farms, the main frequency components of current and voltage during faults are identified mathematically and then verified by simulations. The results show that the frequencies of current and voltage at the terminals of outgoing transmission lines are inconsistent. Following the feature of frequency inconsistency, the adaptability of differential protection is analyzed, and it is found that differential protection for an outgoing transformer in large-scale wind farms may fail once ignoring the frequency inconsistency. Simulation studies demonstrate that inconsistent frequency characteristics will deteriorate the sensitivity and reliability of differential protection. Finally, several suggestions are provided for improving the performance of relay protections for large-scale DFIG-based wind farms.
Highlights
Wind power has been recognized as one of the most cost-efficient sources of renewable energy [1].Along with the rapid development of wind turbines, the capacity of a wind farm connected to the power grid is becoming larger and larger
The main contributions of this paper include: (1) the fault behavior of crowbar-protected doubly fed induction generator (DFIG)-based wind turbines integrated with a power grid is analyzed thoroughly to identify the frequency components of short-circuit current and voltage, which shows the fact that there exists frequency inconsistency for large-scale DFIG-based wind farms integrated with a power grid during faults; (2) following the inconsistent frequency characteristics of the currents, the adaptivity of traditional differential protection on outgoing transformers of large-scale DFIG-based wind farms is investigated and demonstrated with simulations; and (3) several suggestions on improving the reliability of differential protection for large-scale wind farms are proposed
When transmission line faults, that is, the typical ground faults discussed here, occur in a large wind farm, especially for those grounded with low resistance, the short-circuit current contributed by DFIG wind turbines deviates from grid frequency, which may result in failures of the differential protection
Summary
Wind power has been recognized as one of the most cost-efficient sources of renewable energy [1]. The main contributions of this paper include: (1) the fault behavior of crowbar-protected DFIG-based wind turbines integrated with a power grid is analyzed thoroughly to identify the frequency components of short-circuit current and voltage, which shows the fact that there exists frequency inconsistency for large-scale DFIG-based wind farms integrated with a power grid during faults; (2) following the inconsistent frequency characteristics of the currents, the adaptivity of traditional differential protection on outgoing transformers of large-scale DFIG-based wind farms is investigated and demonstrated with simulations; and (3) several suggestions on improving the reliability of differential protection for large-scale wind farms are proposed.
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