Determining Optimised Harmonic Filter Locations in a Meshed Power System – A Case Study from Denmark

The green transition calls for restructured and expanded transmission systems across the world. For Denmark, this means widespread use of underground cables in combination with overhead lines. Increased use of underground cables is known to cause measurable changes in the propagation of harmonic voltages in the grid as well as lower resonance frequencies, resulting in multiple harmonic resonances occurring within the 2nd‐50th harmonic range increasing the risk of distortion amplification. For coping with excessive harmonic distortion, it can be necessary to apply mitigating equipment.

Four philosophies for identifying possible primary filter locations in the meshed grid have been proposed by Energinet and in this paper, an analytical evaluation of these philosophies is conducted. This evaluation uses a case study of the Western Danish 400 kV transmission system, and a simple sensitivity index is used to propose additional candidates for placing the filter as alternative to the primary locations, leading to a finite set of substations to be evaluated as filter location candidates. A passive filter with a fixed rating and harmonic characteristics (a second order high‐pass filter, 11th harmonic tuning order and quality factor of 2) is applied to the set of substations. The results are then comparable across the four philosophies and across the set of substations.

The advantages and disadvantages of each philosophy are evaluated and a ranking in relation to the efficiency of the filter effect is presented. The results obtained with the analytical methodology used in this paper corresponds with conclusions based on comprehensive simulation efforts performed by Energinet for this mitigation assessment.