Behaviour analysis of transmission line protection functions in grids with high penetration of renewable sources

This paper presents an assessment of the potential impact of the high penetration of renewable energy sources (RES) on the protection functions for transmission lines. The performed analysis was done on a simulation model of part of a transmission grid with wind farms (WFs) connected to various substations. A dynamic model was used for the wind generators, including fault-ride-though capability and reactive power contribution during faults. Faults were simulated to obtain graphs of (i) short-circuit currents feeding faults and (ii) measurement of apparent impedance seen by a distance protection in relation to the corresponding Mho circles. The analysis of these elements was then used to assess the behaviour of the protection functions . Results show that the magnitude of current contributions coming from generation points considerably decreases when comparing the use of traditional Synchronous Generators (SGs) and WFs. In addition, it was seen that apparent impedance measurements don't suffer distortion regarding the generator's technology and, therefore, the behaviour and response of distance protections in transmission lines remains valid and a correct tripping command would be issued. Further research might include the use of Hardware-in-the-loop (HIL) with protection relays from different vendors and the interaction with more complex and realistic transmission grids.