Harmonic Distortion Prediction Method for a Meshed Transmission Grid with Distributed Harmonic Emission Sources – Eastern Danish Transmission Grid Case Study

Tremendous, fast green transition in Denmark initiates large-scale grid-integration of renewable energy sources, electrification of energy consumption, establishment of PtX and Energy Islands set goals for the transmission grid development, such as establishment of new connections, and grid reconstruction such as extensive substitution of overhead lines (OHL) with underground cables (UGC). The share of UGC in the Danish transmission grid is increasing. Presence of UGC has resulted in that resonances of the harmonic impedance characteristics of the transmission grid are brought within the harmonic order
range coinciding with the harmonic distortion and causing systemwide increase of the harmonic voltage distortion in the 400 kV meshed transmission grid. Transformation of the 400 kV transmission grid arises needs of predicting the harmonic voltage distortion using simulation models to secure an adequate power quality and support investment decisions and harmonic mitigation for the grid stage which is not yet established and differs from the present grid. This paper presents a method of direct simulation of the harmonic voltage distortion, which is developed and applied by Energinet, Transmission System Operator of Denmark, using Eastern Danish 400 kV transmission grid as a case study. The main advantage of direct simulation is possibility to predict whether, where in the transmission grid, and for which harmonic orders, the not yet commissioned connections may cause violation of the IEC planning levels and which mitigation is necessary for bringing the harmonic distortion down below the planning levels with a given margin. Further, this paper briefly presents directions for the
harmonic assessment in Denmark as part of an industrial PhD project by Energinet and Aalborg University. This joint work shall result in a guideline for prediction of the harmonic distortion in a meshed grid such as where and how an analytical approach can replace observational studies with many numerical simulations.