System impact of micro-production

Abstract: The focus in this thesis has been active power from small scale solar production and what possible impacts an increased proportion of small scale production can have, in a larger context, during short circuit (SC) faults in the grid. The main research question prompting this work was whether active power from small scale solar pro- duction can help support voltages during SC faults, and meet LVRT-requirements in the RfG. The simulation work was performed in the tool DIgSILENT PowerFactory. The work was initially to be carried out using data for an actual network. Instead, part of the thesis work was to construct a power network model, for general validity based on an European benchmark model by CIGRE ́. The model is ranging over all voltage levels from 0.4-380 kV, which is unusual for network models and offer new insights. Static simulations of 3 phase bolted (0 Ω) SC faults were carried out for different study cases, each with varying amounts of PV-production filling up the grid. In addition, analyzes were made of actual disturbance recordings in E.ONs grid, alongside unique PMU-registrations of the same faults made at a residential PV-unit. The simulation results in this thesis showed that accumulated active power from small scale PV-units can, theoretically, meet the LVRT-requirements in the RfG for generating modules of category B. The most striking result were a low voltage-node registered a voltage increase of 35.5% with PV-production compared to without active power input. Other nodes in the same simulated study case, rep- resenting a current PV-production scenario, had an increase of about 20% of the voltage. The case with the largest accumulated active power, representing a future scenario, had a notable impact on voltages across the HV(220 kV)-grid. Information and analysis of fault registration showed that small scale units seem to have a rather slow up-ramping of power after disconnection due to faults in the grid. This, in the context of increasing amounts of DER in the grid brings up the inquiry if this will cause disturbances in the power balance. Additionally, registration of a remote 3 phase SC were found to affect a large geographic area and gave such a severe voltage dip that micro-production nearly disconnected. Fault clearing times throughout the grid might need to be further shortened if normal fault clearing could lead to disconnection of micro-production in large areas. Thus, in conclusion, routines of distribution network companies need to start considering impact of extensive micro-production.