Off-field Testing of Grid Scenarios at Medium Voltage in Flexible AC Transmission Systems involving Wind Energy

Abstract

As a result of the geographical location of north-western Germany, the local grid operator EWE NETZ has a pioneer role with respect to the integration of renewable energy sources in existing AC transmission systems. About 7kWh out of 10kWh from EWE NETZ are from renewable sources, which are fed into existing AC transmission systems using FACTS (Flexible AC Transmission System). Currently, electricity from renewable sources such as on- and offshore wind energy farms, biomass, photovoltaics and hydropower are fed into existing power grids in northern Germany. This process drives the medium voltage grid networks into power utilization limits, leading to various operational problems of the modules used in the networks. In areas away from big cities, such as villages and small towns, the low load demand and the high value of power fed into the grid frequently leads to outages of medium power transformers and/or the associated switchgears. In addition, due to long transmission lines, the allowable limits of voltage escalations are often violated. In the context of FACTS, observations by EWE NETZ show that the number of curtailments within the last decade has increased by 7200%! There is an increasing need to study various unstable grid behaviours by looking at switching stations, switch gears, load impedances, frequency variations etc. with respect to varying levels of renewable energy fed into the grid. By emulating the scenarios encountered in the field using a dedicated laboratory at Jade University of Applied Sciences (JUAS), measurements, modelling and model predictive control can be performed successfully.