Design Algorithm of Harmonic Filters in a Meshed Transmission Grid with Distributed Harmonic Emission Sources – Eastern Danish Transmission Grid Case Study

The transmission grid in Denmark undergoes tremendous reinforcement and development due to massive integration of renewables and PtX, stronger market coupling with foreign grids and connection of the Energy Islands. The political goal is that new transmission lines shall, to the most technically feasible extent, be established as underground cables (UGC) and part of overhead lines (OHL) substituted with UGC. The Danish experience has shown that especially 400 kV UGC may cause resonance conditions, which coincide with harmonic orders of the harmonic distortion and increase the harmonic voltage distortion. Establishment of harmonic filters with the right properties, ratings and locations in the transmission grid is among mitigation solutions of excessive harmonic distortion. In the meshed transmission grid, a new harmonic filter may, on the one hand, dampen a specific harmonic order in the given substation, but, on the other hand, become inefficient or even increase harmonic distortion in other substations. Therefore, the harmonic filter design for the meshed transmission grid is a challenging task. This presentation will explain the algorithm developed by Energinet, Transmission System Operator of Denmark, for automated design of harmonic filters in the meshed transmission grids by simulations. The algorithm will be demonstrated using a validated simulation model of the Eastern Danish 400 kV transmission grid for harmonic assessment as
a case study.