Performance Assessment of Distance Protection in UPFC-Compensated Transmission Networks with Integrated Converter-Interfaced Renewable Energy Plants

Today, the Unified Power Flow Controller (UPFC) stands out as one of the most versatile FACTS devices, extensively deployed on transmission lines. However, the presence of UPFC device in the transmission line affects voltage and current signals at the relay location. The commonly used distance relays face greater protection challenges when such compensated transmission networks are integrated with solar plants. This paper evaluates the distance relay performance in five-bus test system by simulating a double phase to ground fault at seventy percent length of the UPFC-compensated transmission line from the relay bus, with and without solar power plant. The quadrilateral relay characteristics are adjusted to ensure fault detection up to a resistance of 10 Ω with synchronous generator. However, when the synchronous generator is replaced with a solar plant, the relay begins to malfunction with fault resistances as low as 0.5 Ω under these operating conditions. To prevent relay maloperation, the tripping boundaries are adjusted. The apparent impedance measured by the relay falls within this modified characteristics, thus enabling accurate fault detection.