Methods for harmonic analysis in meshed transmission systems

The worldwide efforts for transiting the energy systems to renewable and sustainable sources are fundamentally changing the purpose and needs of the transmission systems. For Denmark this means placing power generation at geographical locations with high wind potential, such as the Danish west coast, or rural areas with enough land for solar power plants. Hence power generation is moved far away from the major cities and the majority of power consumption. Greater distance between power generation and power consumption increases the need for expanding the transmission system to transit more power.

Historically transmission lines are primarily built as overhead lines. However, this meets strong opposition from the public in today’s context. Hence the public in affected areas call for new transmission lines being commissioned with underground cables. Integration of new underground cables present a series of technical challenges, one of which is their influence on harmonic propagation. In recent years several examples both in literature and real system experience have identified amplification of harmonic distortion due to resonances caused by cable systems. This has been measured both in radial systems, such as export cables for offshore wind power plants, and more recently within the meshed transmission system.

It is the primary objective of this Ph.D.-project, to develop methods for analysis of harmonic propagation and amplification in meshed transmission systems. The expected outcome is that the developed methods become a robust tool for determining the risk of harmonic amplification due to underground AC cables and for designing of harmonic mitigation measures.