Impact of low (zero) carbon power systems on power system protection: a new evaluation approach based on a flexiblemodelling and hardware testing platform

This paper presents a flexible model and testing arrangement that can be used to mimic the fault infeed characteristics of power electronics converters and evaluate the performance of transmission protection schemes to faults when the system is “converter-dominated”. That is, sources (e.g. renewables) and infeeds (e.g. HVDC interconnectors) that are interfaced to the main power system via converters. Actual protection relays are injected, in real time, using the outputs of the various fault simulations. A range of potential protection issues, including slow tripping, erroneous discrimination and non-operation, are illustrated for particular scenarios. The main contributions of the paper include knowledge of how different protection schemes may be affected by converter-interfaced sources and guidance on possible solutions to the observed problems. Two solution options are highlighted: changes to the fault detection methods used within relays, and/or defining the fault-response elements of future grid codes (and therefore future converter fault responses) to ensure that existing protection schemes will not be adversely affected in future low-carbon, converter-dominated systems.