No abstract

Renewable energy sources (RESs) are typically interfaced to the grid using power electronics which can cause their fault current characteristics to display significant low frequency harmonics and unbalanced sequence impedances. Such current characteristics can lead to the operation failure of fault component based directional relays. To demonstrate the influence of inverter-interfaced renewable energy generators (IIREGs) on directional relays in detail, analytical expressions for the IIREG equivalent positive-and negative-sequence superimposed impedances are derived in this paper. Considering various factors, the angular characteristics of the sequence superimposed impedances are investigated. Based on these attributes, it can be concluded that fault component based directional relays may be unable to operate in some circumstances. A novel high-frequency impedance-based protection scheme is proposed to manage the adaptability problem by determining the fault direction due to a stable impedance angle. The theoretical analysis and the proposed scheme are tested and verified through real time digital simulation (RTDS) simulation and field testing data.

No abstract

No abstract

Due to different fault ride through controls of both the wind farm and the voltage-source converter high-voltage alternating current (VSC-HVDC) converters, the offshore wind farms that are connected to the power system through VSC-HVDCs have unique fault transients. During a fault on AC side transmission lines, the wind farm and the VSC-HVDC together provide faulted current, whose amplitude and phase will be decided by their different control strategies collectively. The fault transients are different from those in the traditional AC grid. Thus, the performance of traditional protection will be affected. In this study, the AC fault current expression is deduced, while the influencing factors on the current's amplitude and phase are analysed in detail. Based on these characteristics, the performance of distance relays under the grid side fault of the VSC-HVDC-connected offshore wind farm integration system is evaluated. Simulations based on PSCAD have verified the theoretical analysis.

No abstract

No abstract

No abstract