Hannu Laaksonen

A case study of a voltage rise problem due to a large amount of distributed generation on a weak distribution network

The paper is a case study about the integration of a relatively large amount of distributed generation into a weak distribution network. The main focus is on a comparison of methods to increase the integration capacity of distributed generation and on technical requirements from the distribution network companys point of view. The methods studied do not require major investments in the network. The paper considers voltage issues and the load transfer capability of a distribution network including wind power mills. The studies are based on real-life distribution network and load curve data.

Enhanced MV microgrid protection scheme for detecting high-impedance faults

In the future, most microgrid connected distributed generation (DG) and energy storage units will be inverter interfaced with limited fault current feeding capabilities. In addition, during islanded microgrid or islanded operation high fault currents from the utility grid are not available. Therefore new microgrid protection schemes are needed. Previously a new protection scheme was proposed which included both short-circuit and earth-fault protection for island operated medium-voltage microgrid having multiple protection zones without the need for high-speed communication. The proposed protection scheme was not dependent from fault current contribution of the DG units and was selective with the DG unit low-voltage-ride-through curves. In this paper, MV microgrid protection scheme is enhanced so that it will also include, for example, high-impedance-fault detection for downed conductors. Also other protection scheme improvement possibilities, like DG unit high-voltage-ride-through curve compatibility and use of adaptive start/pick-up setting, will be presented in the paper.