Supraharmonics and Grid Operators

Supraharmonics A New Challenge For Grid Operators

Electric mobility is the key to climate-friendly mobility all around the world. Particularly when operated using renewables-based electricity, electric vehicles generate much less CO₂

More and more cars require an increasing number of charging stations, which are usually installed in low voltage grids and effect the power network not only by additional power demand but also by emitting electromagnetic emissions in high frequency range.

These emissions are caused by the power electronics of the EV’s internal charging unit. The switching frequency of these devices varies significantly depending on the manufacturer, field measurements showed frequencies between 10 kHz and 120 kHz. Classical power quality analysers usually provide a frequency analysis range up to 2.5 kHz or 5 kHz, and are not designed for this type of evaluation.

At the same time, more and more decentralised renewable production units and battery storage systems are installed in the grid. The self-commutated inverters and the active rectifying of these units are also a source for supraharmonic disturbance levels, which can interfere with disturbance levels from EV chargers.

The A-Eberle PQ-Box 300 is equipped with a special high-frequency measurement board, which makes it possible to analyse disturbances up to 170 kHz in a fast and intuitive way.

What are supraharmonics and which standards are applied?

Classical harmonics are defined as integer multiples of the mains fundamental frequency. Common measurement devices measure harmonics up to the 40th, 50th or 100th order. Disturbances in the higher frequency range are called supraharmonics (supra = beyond classical harmonics) and are measured as frequency bands, which are independent of the mains frequency.

In the past, voltage levels in the supraharmonic frequency range have not been considered in national and international grid standards. Due to the increasing impact of high-frequency emissions in low voltage grids, IEC 61000-2-2 (2018) standard was the first to define compatibility levels for the frequency range between 2 and 150 kHz. IEC 61000-2-2 is a common international practice and often used as a reference by national recommendations (eg. G5/4 or G5/5 in the UK).

The tables below show limit values of the supraharmonic frequency range. The limits below 9 kHz are defined as a percentage of fundamental oscillation, whereas the limits between 9 and 150 kHz are given in dB(µV) which is a common unit for EMC standards.

Table 1: Compatibility levels of 2 to 9 kHz range according to IEC 61000-2-2

Table 2: Compatibility levels of 9 to 150 kHz range according to IEC 61000-2-2

Table 3: Relation between the units

Evaluation and Reporting / Supraharmonic Survey

The survey of supraharmonic signals takes power quality analysis to a completely new level and therefore requires highly intuitive software.

The usage of the powerful A-Eberle WinPQ mobil software solution in combination with PQ-Box 300 allows the easy and intuitive evaluation of supraharmonic disturbance levels. Clearly arranged graphics such as high-quality PDF reports help to understand disturbance patterns and find causes for problems in the grid.

It is possible to compare the measured disturbance levels with IEC 61000-2-2 emission levels or custom defined limit curves in online and offline analysis.

Disturbance Sources and Effects

Typical sources for supraharmonic disturbances are:

• Variable frequency drives (VFD) with active frontend
• Rectifiers with active power factor correction (PFC)
• Self-commutated inverters of eg. PV plants, battery storage systems or EV chargers
• Power line communication systems (PLC)

Supraharmonics short-term and long-term effects on other loads connected to the network. Typical disturbances are:

• Abnormal noise of power supply units, transformers, electric ovens, …
• Reversible malfunctions of devices with touch control
• Light flickering of LED lamps
• Thermal stress to capacitors in input circuits or filters
• Lifetime-reduction of electrical equipment due to thermal stress

Top 3 FAQs

What are the benefits of measuring high-frequency disturbances?

Being aware of supraharmonic disturbance levels in your grid helps to prevent premature aging of power electronic components, especially DC link capacitors. Ensuring that there are no supraharmonic disturbances in the grid can help to prevent mismeasurement of energy meters and thus financial losses.

Which high-frequency disturbance levels are dangerous for my equipment?

Acoustic noise is caused by supraharmonic voltage components with a frequency of up to 15 kHz with amplitudes from 0.5 % upwards. Overheating of capacitors usually appears at amplitudes greater than 1 %. The heating effect increases with the frequency of the voltage component.

How to mitigate supraharmonic disturbances?

The mitigation of supraharmonic noise is much easier to do than the measurement. Passive filters can effectively mitigate the disturbance levels.

With the change in electric power grids due to electro mobility (e-mobility) and renewable energy production, the number of sources for supraharmonic disturbances is constantly increasing, and so are its associated problems.

With IEC 61000-2-2, the first low-voltage grid, standard having already adapted its compatibility levels to the new range, and other standards such as G5/5 expected to follow.

The PQ-Box family offers all the tools needed to be prepared for future requirements. The intuitive usage of the devices as well as our experience with these new challenges guarantees a fast and easy evaluation of the whole power quality spectrum.

PQ-Box 150 and PQ-Box 200 can be used for permanent measurement of frequency components up to 9 kHz. A-Eberle PQ-Box 300 as the dedicated high-frequency tool covers the full frequency spectre up to 170 kHz.