Undesired islanding of MV networks sustained by LV dispersed generators compliant with present grid code requirements

摘要

As a consequence of the increasing penetration of distributed generation from renewable energy sources into power systems, international authorities have provided the rules for the connection of active end-users to distribution networks. Power regulating functions have been recently introduced in European grid codes aiming to support voltage and frequency stability. In this paper, the effects of the adoption of such regulating functions have been widely examined, emphasizing the risk of uncontrolled islanding on a Medium Voltage network as the amount of static generators connected to Low Voltage subsystems increases. The study investigates the performances of both existing regulating requirements, such as active and reactive power modulation according to local frequency and voltage, and the additional contribution of further stabilizing functions, such as Inertia Emulation and Fast Voltage Support. Furthermore, the interaction between power regulating rules, generators protection systems and automatic reclosing procedures applied by the Distribution System Operator to circuit breakers at sending end of Medium Voltage feeders, are investigated. The presented results, carried out making use of DIgSILENT PowerFactory software, well demonstrate the correlation between regulating functions applied to generators and the islanding phenomenon.