Measurement and analysis of harmonic data to assess the impact of installations connected to high voltage systems

Inverter-based technologies are increasingly applied in high and extra high voltage systems. In addition to that, overhead lines are replaced by underground cables due to spatial planning needs of society. The use of more underground cables causes changes in the resonance frequencies of the power supply system impedance, which can result in either amplifying or reduction of harmonic levels in power supply systems. A practical harmonic assessment of the impact of a distorting installation on an extra high voltage grid is for a real installation complicated. Articles are published on the methods, but not many describe real cases in high voltage grids. This paper analyses a harmonic case with actual measurements. The analysis is based on the non-invasive method [1]. In this particular case, when the disturbance originates from the grid, an assessment can be performed with known filter states and calculated filter impedances. The 7^th harmonic has its origin in the grid. In case of the other harmonic orders it cannot be concluded that, either the disturbance is due to the grid, or due to the distorting installation, or both. In these cases the power directions varies in time.