Towards a Tool for Assessing Frequency Stability in Islanded Distribution Grids, Based on a Newly Developed Python RMS Simulation Program Built on the PandaPower Framework

The emergency operation of distribution networks as islanded grids - temporarily independent from the interconnected transmission system - can enhance power supply resilience. Such networks typically exhibit low inertia, making frequency stability a key concern. Until now, islanded operation has mainly been considered for system restoration under transmission system operator (TSO) responsibility, leaving distribution system operators (DSOs) with little experience in assessing frequency stability. Commercial tools are expensive and tailored to TSO needs, motivating the development of simple, cost-effective solutions for evaluating and monitoring frequency stability in potential islanding scenarios. In this work, a dynamic phasor-based simulation tool was developed to assess frequency stability. It uses the PandaPower data structure to model the network and includes essential components such as lines, buses, loads, and generators with their controllers. The tool is successfully validated against PowerFactory and applied to a real section of a distribution network in a hypothetical islanded mode, using rate of change of frequency (RoCoF) and frequency nadir as stability indicators while considering single and double contingency scenarios.

Keywords: frequency stability, rate of change of frequency, frequency nadir, online dynamic security assessment, phasor-based time domain simulation, pandapower, distribution network, island operation.