Supraharmonic Distortion in MV and LV Grids — Four Documented Negative Effects and the Limits Gap
| Paper type | Comprehensive analytical review — University of Genova & University of Bologna, Italy |
| Frequency range addressed | Supraharmonics: 2 kHz – 150 kHz (beyond conventional harmonic analysis) |
| Four documented effects | Power loss & heating · Dielectric aging · MV cable termination failure · PLC interference |
| Propagation finding | Strong correlation measured between substations 16 km apart — SH propagates over long distances in MV networks |
| MV/LV transformer transfer | Transfer ratio 0.5 to 3.0 — some SH components are amplified when crossing from MV to LV |
| Capacitor interaction | Input capacitors of nearby loads attract SH currents — reducing propagation but accelerating capacitor aging and causing premature failures |
| Regulatory status | No planning or compatibility limits exist above 9 kHz in distribution network standards — active standardisation gap |
| Source | Mariscotti A, Mingotti A. Sensors 2024, 24(8), 2465. DOI: 10.3390/s24082465. Open access CC BY 4.0. |
01 Context — A New Frontier of Network Stress
The conventional power quality framework addresses harmonic distortion up to the 40th order — 2 kHz at 50 Hz. Above 2 kHz, the supraharmonic range (2–150 kHz) was historically considered non-problematic: the power electronic devices of the 1980s and 1990s switched at frequencies below or only slightly above this threshold, and their emissions in the supraharmonic range were modest. This assumption no longer holds.
Modern power electronics — PV inverters, EV chargers, battery storage converters, and LED drivers — use Silicon Carbide (SiC) and Gallium Nitride (GaN) switching devices at frequencies of 20–100 kHz or higher. These devices place their primary switching energy directly in the supraharmonic range. The result is a rapid and widespread contamination of distribution networks with conducted emissions in a frequency band where no emission limits exist, no measurement standards are adequate, and the negative effects on network assets and connected equipment are only beginning to be systematically documented.
The 2024 paper by Mariscotti and Mingotti at the Universities of Genova and Bologna provides the most comprehensive published analysis of supraharmonic effects on MV and LV distribution networks — covering four distinct negative effect categories, propagation characteristics, transformer transfer behaviour, and the implications for standardisation. It is based on approximately 70 documented references spanning a decade of supraharmonic research.
Supraharmonics are not simply “faster harmonics” — their propagation and aggregation behaviour differs fundamentally from classical harmonics. Classical harmonics (below 2 kHz) are synchronised to the mains frequency, propagate predictably through network impedances, and can be modelled by superposition. Supraharmonics have nearly random phase distribution between devices — they partially cancel when aggregated from multiple sources — but they also create network resonances that can amplify specific frequency components locally. Their time behaviour is intermittent and time-varying, unlike the relatively steady classical harmonic spectrum. These differences require different measurement approaches, different modelling tools, and ultimately different limit frameworks.
02 Four Documented Negative Effects
The study identifies and documents four principal categories of negative effects from supraharmonic distortion on MV and LV network assets and connected equipment:
Power Loss and Heating
At supraharmonic frequencies, skin effect concentrates current on the conductor surface, reducing the effective cross-section and increasing resistance. Cables, transformer windings, and neutral conductors carrying supraharmonic currents run hotter than their power-frequency loading alone would predict. Standard thermal ratings based on power-frequency current are non-conservative in the presence of significant supraharmonic content. Dielectric losses in cable insulation also increase with frequency — the I²R heating mechanism is compounded by dielectric heating within the insulation material itself.
Dielectric Material Aging
Elevated electric field intensity at supraharmonic frequencies accelerates dielectric degradation through two mechanisms: partial discharge events (more likely at high field intensities) and dielectric loss heating. Both mechanisms are accelerated by higher frequency — the number of stress cycles per unit time increases proportionally with frequency. A dielectric material exposed to 50 kHz supraharmonics experiences 1,000 times more electrical stress cycles per second than at 50 Hz. This dramatically accelerates aging in cable insulation, capacitor dielectrics, and transformer insulation — particularly in MV equipment where field intensities are already high.
MV Cable Termination Failure
The most severe documented consequence of supraharmonic distortion on MV network assets is failure of cable terminations. MV cable terminations are geometrically complex — the transition from the cable’s controlled electric field geometry to the air-insulated connection involves stress relief components (stress cones, field grading materials) designed for power-frequency operation. Supraharmonic currents produce localised heating and elevated electric field stresses at these terminations that the original design did not account for. The combination of dielectric stress and local heating has caused premature termination failures in MV networks with high renewable energy penetration.
PLC Interference
Power line carrier communications — used for smart metering (DLMS/COSEM), demand response, grid control, and EV charging management — operate in the 9–148 kHz frequency range (CENELEC bands A–D). This frequency range overlaps directly with the supraharmonic range. Supraharmonic emissions from PV inverters, EV chargers, and LED drivers can overwhelm PLC signals, causing metering errors, communication failures in demand response systems, and loss of remote monitoring capability. The circular interference problem in EV charging — where the EV charger’s switching emissions disrupt the PLC communication intended to manage EV charging — is an immediately practical manifestation of this effect.
03 Propagation — Further Than Expected
One of the most significant and practically important findings in the supraharmonic literature is the long-distance propagation of supraharmonic disturbances in MV networks. A strong correlation was measured between supraharmonic levels at two MV substations 16 km apart — demonstrating that a supraharmonic source at one point in the network can affect equipment at substations several kilometres away. This is far beyond the local neighbourhood coupling that engineers intuitively assume for high-frequency conducted emissions.
The Swedish MV network measurement
Field measurements on a real Swedish MV network with eight feeders — including a small wind farm — confirmed supraharmonic propagation across the entire network. The wind farm’s inverter switching frequencies were detectable at all monitoring points across the eight feeders, with the amplitude varying according to the network impedance at each location. The study also found that larger MV networks have more resonant frequencies but lower resonance peak amplitudes — a network impedance characteristic that affects how supraharmonics propagate and where they are amplified.
Input capacitors of loads connected near the supraharmonic source act as low-impedance paths at high frequencies — they attract supraharmonic currents that would otherwise propagate further into the network. This localises supraharmonic energy near the source and reduces long-distance propagation, which appears beneficial for distant equipment. The cost is accelerated aging and premature failure of the capacitors themselves — which are now absorbing the energy that would otherwise have spread across the network. This is a classic hidden failure mechanism: the protection of distant equipment comes at the expense of accelerated degradation in nearby equipment, without any visible indicator until the capacitor fails.
04 Transformer Transfer — Some Components Are Amplified
The transfer of supraharmonics through MV/LV distribution transformers is not a simple attenuation process. Measurements of transformer transfer ratios at supraharmonic frequencies show a range of 0.5 to 3.0 — meaning that for some frequency components, the supraharmonic amplitude on the LV side is up to three times higher than on the MV side. Some supraharmonic components are amplified in crossing the transformer.
This amplification occurs due to the complex impedance interactions between the transformer’s leakage inductance, winding capacitances, and the capacitive loads connected to the LV side. At certain frequencies, the transformer and connected LV network form a resonant circuit that amplifies voltage at the resonant frequency. The resonant frequencies depend on the transformer design, the cable lengths, and the capacitance of connected loads — all of which vary with load configuration and feeder layout.
A utility engineer who measures supraharmonic distortion at the MV side of a distribution transformer and finds it within acceptable levels — if such levels existed — cannot conclude that the LV supply delivered to customers is also acceptable. For certain frequency components, the LV distortion can be significantly higher than the MV distortion. This means that MV-side monitoring alone is insufficient for assessing customer-side supraharmonic exposure. LV-side measurement is essential wherever supraharmonic effects on LV-connected equipment are of concern.
05 The Limits Gap — No Rules Above 9 kHz
The most significant regulatory gap identified by Mariscotti and Mingotti is stark: no planning levels or compatibility limits currently exist in distribution network standards for supraharmonics above 9 kHz. The CENELEC EN 50160 standard, which defines voltage characteristics for public LV networks, addresses frequency deviation, voltage magnitude, harmonics up to the 25th order, and flicker — but contains no limits for the supraharmonic range. IEC 61000-2-2 addresses compatibility levels for LV networks up to 2 kHz. Above 2 kHz, the only relevant limits are in CISPR standards (above 150 kHz, for EMC) and the narrow CENELEC signalling frequency bands — leaving the entire 9 kHz to 150 kHz window unregulated from a distribution network PQ perspective.
Mariscotti and Mingotti derive indicative limits for supraharmonic distortion based on the documented effect thresholds — using the same physical reasoning applied to derive harmonic limits from equipment sensitivity data. Their derived limits provide a quantitative framework that did not previously exist in the literature. These limits have been submitted to the ongoing standardisation process at IEC SC 77A WG9, which is actively revising IEC 61000-4-30 to address supraharmonic measurement. However, the gap between documented effects, derived limits, and enforceable standards remains wide — and in the interim, network operators have no regulatory basis for requiring equipment manufacturers to control their supraharmonic emissions.
The absence of limits has two practical consequences for distribution network engineers. First, there is no objective basis for requiring mitigation when supraharmonic disturbances are identified — making it difficult to compel action from the equipment owner whose device is the source. Second, when equipment fails prematurely — a capacitor, a cable termination, a PLC metering system — the connection to supraharmonic disturbance is difficult to establish because no baseline measurements were required, no alarm levels were defined, and no monitoring was in place.
06 Power Quality Perspective
This case study is a companion to CS04 (PV Inverter Supraharmonics) and CS07 (EV Charger Supraharmonics) — it addresses the network-level consequences of the source-level emissions documented in those case studies. CS04 and CS07 characterise what individual devices emit. CS08 documents what happens to the network and its assets when those emissions are present at scale.
From a utility engineering perspective, the MV cable termination failure finding is the most immediately actionable. Cable termination failures in MV networks are expensive — replacement requires switching out the affected cable section, mobilising a jointing crew, and managing customer interruptions. If supraharmonic distortion from renewable energy converters connected to the same MV feeder is contributing to accelerated termination aging, the utility is bearing maintenance and capital costs caused by the behaviour of customer-side equipment, with no regulatory mechanism to attribute those costs or require the source to mitigate its emissions.
You cannot manage what you do not measure. The practical first step for any distribution network operator concerned about supraharmonic effects is deployment of supraharmonic-capable monitoring — instruments with sampling rates above 300 kHz, capable of capturing the full 2–150 kHz range. The cost of a Class A PQ monitor with supraharmonic capability has fallen dramatically in the last five years, and the EU-funded ADMIT project (Accurate Measurement of Distorted Instruments and Transformers) is developing the instrument transformer accuracy standards needed for MV-level supraharmonic measurement. For utilities with high renewable penetration on MV feeders — wind, PV, battery storage — establishing a supraharmonic baseline now will be far less expensive than explaining premature MV infrastructure failures later without any measurement history to support root cause analysis.
References
- Mariscotti A, Mingotti A. “The Effects of Supraharmonic Distortion in MV and LV AC Grids.” Sensors, 24(8), 2465, 2024. DOI: 10.3390/s24082465. Open access CC BY 4.0.
- Rönnberg SK, Wahlberg M, Bollen MHJ. “Evaluation of Medium Voltage Network for Propagation of Supraharmonics Resonance.” Energies, 14(4), 1093, 2021. DOI: 10.3390/en14041093.
- IEC 61000-4-30:2015+AMD1:2021. Electromagnetic compatibility — Part 4-30: Power quality measurement methods. IEC, Geneva. (Under revision by SC 77A WG9 to address supraharmonics.)
- EN 50160:2010+A3:2019. Voltage characteristics of electricity supplied by public electricity networks. CENELEC, Brussels.
- IEC 61000-2-2:2002+AMD1:2017. Electromagnetic compatibility — Compatibility levels for LV supply systems, 0–2 kHz. IEC, Geneva.
- ADMIT Project. Accurate Measurement of Distorted Instruments and Transformers. EU-funded research project. Available: admit-project.eu
Mariscotti A, Mingotti A. “The Effects of Supraharmonic Distortion in MV and LV AC Grids.” Sensors (MDPI), vol. 24, no. 8, p. 2465, April 2024.
DOI: 10.3390/s24082465 · Full text at PMC → — Open access CC BY 4.0.
This case study is presented in summary and commentary form for educational purposes. SVG diagrams and the PQ Perspective section (Section 6) are original IPQDF editorial content by Denis Ruest, M.Sc. (Applied), P.Eng. (ret.). IPQDF does not claim authorship of the original research.