Abstract
Renewable energy sources 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 and field testing data.
Highlights
Renewable energy sources (RESs) such as wind power and photovoltaic (PV) power have experienced rapid development in recent years in an attempt to reduce reliance on fossil fuels and associated pollution [1,2]
It can be seen from the above expressions that the amplitude and the phase angle of the inverter-interfaced renewable energy generators (IIREGs) equivalent negative-sequence superimposed impedance are only related to the control strategies and fault conditions
When a fault occurs in the interior of the IIREG power plant, the equivalent impedance measured at D is reflected by the impedance characteristics of the traditional synchronous system
Summary
Renewable energy sources (RESs) such as wind power and photovoltaic (PV) power have experienced rapid development in recent years in an attempt to reduce reliance on fossil fuels and associated pollution [1,2]. Distance protection has been investigated in [15,16,17,18], while literature [15,16] studied the impact of the non-power frequency fault current from doubly fed induction generator (DFIG) based wind farms on distance protection and proposed solutions It was determined in [17] that the weak feed of inverter-interfaced renewable energy generators (IIREGs) could amplify the influence of the fault resistance and a corresponding solution was proposed in [18]. Expressions for the equivalent sequence superimposed impedances were not deduced in this study, and the influence mechanism of fault component based directional relays requires further investigation. Derive the equivalent positive- and negative-sequence superimposed impedance expressions, it is necessary to know the positive- and negative-sequence voltages and currents of IIREGs before and during a fault
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