Adaptability Analysis of the Directional Relay for the System with Inverter-interfaced Renewable Energy Generators

With the environmental pollution and energy crisis, renewable energy sources (RES) are developing rapidly. Among them, the inverter-interfaced renewable energy generators (IIREGs) are an important component. Its fault characteristics are significantly different from those of synchronous generators (SGs), which are affected by the control strategy of inverters, and mainly shows the limited current amplitude and unstable internal impedance, so the traditional directional relays installed at the high-voltage transmission line face the risk of refusal for the fault located in the positive direction. In order to analyze the influence of IIREGs on the directional relays, its equivalent positive- and negative-sequence superimposed impedance is calculated. On this basis, sequence impedance angles are studied under different influencing factors. It is found that the sequence impedance angles are unstable and the traditional directional element has high risk of refusal. This existing protection has been confirmed by simulation results on the real-time digital simulation (RTDS) platform and field-testing data.