Positive Sequence Relaying Method for Solar Photovoltaic Integrated Distribution System

For fault ride-through requirement, solar photovoltaic (PV) plant remains connected to the grid during a fault. In such a situation, a PV plant operates in different modes and supplies current to comply with the requirements of the grid. The relative magnitude of phase current contributed by a PV plant during a fault is at par with the nominal current. Such a fault behavior restricts the application of available phase current based relaying approaches while protecting the distribution system with a PV plant. A protection method using local positive sequence voltage and current is proposed to protect a distribution system with PV plant. The method selects pickup current using proposed current-voltage curve for fault detection. A three-dimensional time-current-voltage characteristic is proposed for trip time calculation. Performance of the proposed method is tested for relays on both PV plant side and grid end using DigSilent PowerFactory simulation data for a CIGRE 14-bus distribution system with PV plant having different modes of operations. The method is found to be accurate and comparative assessment reveals its superiority.