Harmonics_and_Interharmonics_in_a_Power_Transmission_System

Danish Transmission System Operator ELTRA has recognized that harmonic currents and voltages propagate in their 400 kV transmission grid. It is due to minor operational malfunctions as for instance protective relays malfunctioning because of non-sinusoidal currents and voltages. The prescence of harmonic distortion has been also confirmed by several measurements. The causes of this increasing amount of harmonics in the transmission system are unravelled. The content of (inter)harmonic distortion is constantly changing, somehow depending on the composition of the generation and the load,network configuration, etc. Some preliminary investigations suggests that an increasing amount of installed rated power of 400/150 kV autotransformers aggravate the problem. Harmonic currents specifically gives rise to problems concerning the protection of DC-side filter of the Konti-Scan HVDC link in Vester Hassing. To solve the problem, ELTRA has formulated and proposed a Ph.D. project to be carried out in cooperation with Aalborg University. The Ph.D. project will contain state-of-the-art analysis of harmonic and interharmonic propagation at the transmission level, models of the transmission system including connected HVDC links, relevant transmission components, models of power production and load units and methods for measuring harmonic currents and voltages at the transmission level. Special weight will be attached to the autotransformer model and interractions between HVDC links and the rest of the AC grid. All these models will be validated by proper and accurate measurements.