The Effects of Supraharmonic Distortion in MV and LV AC Grids

Since the integration of electronic devices and intelligent electronic devices into the power
grid, power quality (PQ) has consistently remained a significant concern for system operators and
experts. Maintaining high standards of power quality is crucial to preventing malfunctions and faults
in electric assets and connected loads. Recently, PQ studies have shifted their focus to a specific
frequency range, previously not considered problematic—the supraharmonic 2 kHz to 150 kHz range.
This range is not populated by easily recognizable harmonic components of the 50 Hz to 60 Hz
mains fundamental, but by a combination of intentional emissions, switching non-linearities and
byproducts, and various types of resonances. This paper aims to provide a detailed analysis of
the impact of supraharmonics (SHs) on power network operation and assets, focusing on the most
relevant documented negative effects, namely power loss and the heating of grid elements, aging
of dielectric materials, failure of medium voltage (MV) cable terminations, and interference with
equipment and power line communication (PLC) technology in particular. Under some shareable
assumptions, limits are derived and compared to existing ones for harmonic phenomena, providing
a clear identification of the primary issues associated with supraharmonics and suggestions for the
standardization process. Strictly related is the problem of grid monitoring and assessment of SH
distortion, discussing the suitability of normative requirements for instrument transformers (ITs)
with a specific focus on their accuracy.