Phasor Measurement Unit (PMU) based power system analysis of MV distribution grid

Abstract

The introduction of renewable energy sources such as wind, CHPs, photovoltaic in the electrical power networks has coined the term of distributed generation (DG) penetration into the electrical power grids. Often this DG penetration is concentrated in the distribution grids leading to complex electrical behaviour, in terms of power flow and voltage of the distribution grid. At present, the understanding of stability and dynamic behaviour of the medium voltage distribution grids as a result of increased DG penetration is limited. As a consequence, there is a need to improve the present monitoring of medium voltage (MV) electrical distribution grids. This has prompted Delta Network Group (DNWG), one of the Distribution Network Operator (DNO) of the Netherlands to install Phasor Measurement Units (PMUs) in their 50 kV Delta ring distribution grid resulting in increased observability of the 50 kV distribution grid. However, with the increased observability there is a need to analyse the distribution grid based on the data generated by the PMU monitoring system. The aim of this thesis, is to analyse and evaluate the 50 kV Delta ring distribution grid in terms of steady state and dynamic voltage and power flow behaviour based on the real time data acquired from the PMUs. The approach involves at first modelling the Delta distribution grid under study in PowerFactory software. The grid is modelled partly in detail based on actual parameters of components like 50 kV cables, transformers, CHP synchronous generators and assuming already available standard generic models for distributed generation like wind turbines, and controller models for CHP plants. The software model forms the basis for analysis of the distribution grid; at first the instantaneous steady state power flow behaviour based on PMU and SCADA data. Furthermore, evaluating the distribution grid during two contingencies considered as case studies; -Switching out a 50 kV cable. (contingency in the 50 kV distribution grid) -Loss of generation from wind power plant. (contingency in the 0.4/10 kV sub distribution grid) The contingencies are actual past grid events observed by the PMUs and using this data, along with the data from the SCADA monitoring system the contingencies are simulated, analysed in terms of power flow and voltage behaviour. The results for each contingency are compared with the PMU and SCADA monitoring system. The analysis reveals the bi-directional power flow nature in the Delta distribution grid majorly influenced by the variation in the distributed generation. Extending the analysis in case of contingencies, the common observations during both the cases show slight changes in voltages and redistribution of power flow in the 50 kV distribution grid. The voltage fluctuations are within the stable operating limits. A possible explanation for this is the connection of the Delta 50 kV ring distribution grid to a secure 150 kV transmission network of the Netherlands. The power balancing of the distribution grid is also done by the 150 kV transmission network in both the cases without having a significant impact on the response of the distributed generation during both the cases studied. Lastly, the work conducted in this thesis provides an insight and a general framework into analysing the Delta MV distribution grid containing distributed generation based on the data obtained from the PMU monitoring system.