Publishable Summary for 19ENG06 HEFMAG

updated June 2022

Metrology of magnetic losses in electrical steel sheets for high-efficiency energy conversion

Overview

Magnetic steel is used for electric motors/generators and transformers, and in both cases the energy losses occurring in the cyclic magnetising of the material are significant. Due to the drive to increase energy efficiency, improved methods are required to assess these energy losses. This project aims to develop and validate methods and experimental setups for traceable magnetic loss measurements in thin magnetic steel sheets extending the induction, frequency and temperature ranges beyond the current IEC 60404 standards, and to study and model power losses under real operating conditions. This will facilitate improved design and performance of magnetic and power electronics devices in support of the Ecodesign Directive 2009/125/EC and the goals of the United Nations 2030 Agenda for Sustainable Development.

Need

The drive to improve energy efficiency, reduce consumption and curb CO2 emissions has led to the introduction of increasingly stringent EU and national legislation related to energy efficiency and emissions reduction. Magnetic steel sheets are the core of electric motors, generators, and transformers, which produce and convert virtually all the energy obtained from conventional and renewable sources. Due to the cyclic magnetising of the steel sheets the energy losses that occur are very significant and can easily reach up to 10 %. The ongoing drive for miniaturisation of devices and high-speed rotating machines require increased working frequencies, and steel producers are therefore striving to develop thinner and highly energy-efficient grain-oriented (GO) and non-oriented (NO) magnetic steels, with enhanced permeability, suitable for kHz frequencies. Novel products based on electrical steel require magnetic loss measurements and modelling under extreme operating conditions, with high temperature, 2D excitation, distorted flux with high harmonic content, skin effects and dc currents.

Objectives

The overall objective of the project is to support the development and characterisation of high efficiency electromagnetic machines (e.g. electric motors and transformers), which operate close to saturation induction and at high temperatures and frequencies, through (i) the development and validation of methods and experimental setups for traceable magnetic loss measurements in thin magnetic steel sheets extending the induction, frequency and temperature ranges beyond the current IEC 60404 standards and (ii) the study and modelling of power losses under real operating conditions, thus facilitating improvements in the design and performance of magnetic and power electronics devices as required by the Ecodesign Directive 2009/125/EC.

The specific objectives of the project are:

1.  To build and validate an improved metrological infrastructure for the determination of power losses with relative standard deviation () down to 1 %, using Single Sheet and Epstein frame magnetic circuits in electrical steel laminations at induction values close to saturation and at frequencies ranging from DC to 10 kHz with flux waveforms of different harmonic content. The dynamic magnetic characterisation will target novel thin laminations with thickness as low as 0.10 mm for non-oriented steels and 0.18 mm for grain-oriented materials.

2.  To build and validate a new metrological infrastructure for Epstein frame measurements up to 155 °C, corresponding to the “F class” insulation (IEC 60085 and IEC 60034-1), to match the typical operating temperatures of electric motors, with a direct impact on loss and efficiency evaluation, since the current standard measurement temperature is 23 °C ± 5 °C.

3.  To study and model power losses in thin sheets within a DC-MHz frequency regime, with the help of fluxmetric, magneto-optical characterisation techniques as well as scanning probe techniques for the sub‑µm regime.

4.  To use one-dimensional and two-dimensional measurements and physical models, taking into account the non-uniform flux profiles due to the skin effect, in order to bridge the gap between standard loss characterisation under ideal conditions and real operating condition of state‑of‑the‑art magnetic devices. To also emulate the two-dimensional flux loci arising in the non-oriented steel laminations in the stator core of a rotating machine.

5.      To facilitate take up of the results by industry, NMIs and standardisation bodies (IEC TC 68 and ISO/TC201/SC 9) by providing updates on magnetic imaging techniques and good practice guides for improved traceable magnetic loss measurements at higher frequency and induction, allowing for an evolution of the current IEC 60404 standards for loss measurement reflecting up-to-date industrial needs.

Progress beyond the state of the art

To date, intercomparisons on measurements of magnetic loss measurements involving NMIs and stakeholders have been performed only at 50 Hz, yet modern electrical machines are excited at higher induction and higher frequencies. This project will extend the frequency and induction range of traceable and validated loss measurements by performing a round robin test between an Epstein frame and a single sheet tester (SST) at 50 Hz and 400 Hz as well as a new Epstein frame round robin test up to 10 kHz.

At present, all magnetic loss calibration measurements at European NMIs and stakeholders are only carried out at 23 °C ± 5 °C, while electrical machines may operate at temperatures exceeding 100 °C at which saturation magnetisation, anisotropy and electrical conductivity are reduced. This project will develop and validate a new metrological infrastructure for Epstein frame measurements at temperatures up to 155 °C, to match the typical operating temperatures of electric motors.

Alternating power losses can be accurately measured and modelled only under sinusoidal flux conditions, but in many modern electrical machines a very high harmonic content and skin effects are both present. This project will provide and apply a comprehensive approach to physically based wideband loss modelling in the presence of skin effects. This will enable improved loss prediction under arbitrary flux waveforms up to the MHz range on the basis of data measured under sinusoidal flux conditions.

Although at present several experimental techniques are available at selected NMIs and stakeholders for the determination of 2D losses, no measurement standard has been established. In order to bridge the gap between standard loss characterisation under ideal conditions versus real operating conditions of state‑of‑the‑art magnetic devices, this project will use a comprehensive experimental and modelling approach which will compare one- and two‑dimensional measurements at frequencies up to 400 Hz with physical models taking into account the non‑uniform flux profiles due to the skin effect.

The data collected according to the current IEC standards and from additional interdisciplinary experimental techniques are the key ingredients in the study of the energy losses in soft magnetic materials. However, this project will go beyond the current state‑of‑the‑art by providing a necessary update to the standard loss measurement techniques at the European NMIs and stakeholder laboratories, reducing the expanded uncertainty, increasing the temperature and frequency ranges and the peak induction, and by enabling the analysis of losses in the presence of eddy currents and complex harmonic content.

Results

Power losses with standard measurement setups:

A set of FeSi NO, GO and FeCo reference samples for planned round-robin activities were defined and obtained through Stakeholder Committee members. The round-robin protocol draft was written also as a foundation for a good practice measurement guide. After a preliminary check and improvement of the available experimental setups for loss measurements according to the IEC 60404 set of standards, the partners started the round-robin activities using Epstein frame samples and equipment at room temperature in a frequency range from 50 Hz up to 10 kHz, as well as Single Sheet Tester (SST) samples and equipment at room temperature from 50 Hz to 100 Hz. The experimental activities of the project partners have been  concluded in 2022 and the data analysis phase will be concluded in early 2023. The results will be included in the reports to stakeholders and IEC, which are expected to be released early in 2023. An additional round of discussion with Stakeholders was held in December 2021/January 2022, to better define the details of the future activities of the NMIs and the circulation of reference samples among stakeholders. A second poll among Stakeholders was conducted in late summer 2022 to define which samples to ship to each interested Stakeholder. Some selected samples were circulated among them in the fall of 2022, and these activities will continue for the rest of the project.

Power losses under operating temperature conditions:

Subsets of the available Epstein FeSi NO and FeCo samples were identified for high-temperature characterization and the high-temperature round-robin protocol draft was drafted. Available equipment, such as climate chambers, furnaces, and Epstein frames were tested at temperatures up to 155 °C in preparation for this work. Tests were made to assess uncertainty contributions against standard measurements at room temperature with a view to optimizing the setups when operated at temperatures up to 155 °C. Measurements at different temperatures 23°C, 50°C, 100°C, and 155°C were performed on one NO sample and  on one FeCo sample. Some GO and NO Epstein strips were extracted from the round robin sets as reference materials for imaging the magnetisation process also at elevated temperature and subjected to cutting and polishing in preparation for magneto-optical microscopy as well as scanning probe microscopy. Specific optical equipment was also developed and optimised for operation at high temperature in a controlled atmosphere environment. Magneto optical measurements using the Kerr effect were performed at different temperatures ranging from 25°C to 150°C on GO samples. The final microscopy results will be available in 2023 for the drafting of related publications. Experimental loss measurements at elevated temperatures and the relevant analysis will be concluded by Spring 2023.

Alternating power losses in thin sheets up to the MHz range:

Activities in the project are directed to the extension of current declarations of Calibration and Measurement Capabilities (CMCs) and to provide data for the prediction of losses under arbitrary flux waveforms up to the MHz range. FeSi NO, FeCo materials as well nanocrystalline tape samples were provided by stakeholders. The partners already performed checks of the equipment devoted to high-frequency loss measurements and measurements are underway. Measurements and analysis up to 1 MHz by project partners and at least one stakeholder under sinusoidal and non-sinusoidal induction waveforms will be concluded by spring 2023.

Project activities will provide data on the magnetic domain configuration and its evolution with frequency and temperature. The goal is to obtain an in-depth understanding of the role of magnetic domains and domain wall motion in hysteresis and excess eddy current losses, thus providing the basis for the broadband modelling of losses and eddy currents. Samples suitable for magneto-optical and scanning probe microscopy were cut, polished, surface treated and transferred to the partners for the planned analysis of magnetic domains. Magnetic domain observation - not requiring polishing or surface treatments – was performed using a sensor based on magneto-optical indicator films with out-of-plane anisotropy. A new sensor, using a magneto-optical indicator film with in-plane anisotropy and a high-speed camera, was also developed and is now working in two different laboratories with an operating frequency increasing from 1 kHz to 8 kHz.

A numerical code implementing a physical model of domain wall dynamics in GO materials from DC to 10 kHz was developed. Such a model takes into account the domain wall dynamics under a sinusoidal polarization, in particular, the domain wall bowing and non-uniformity of polarization along the thickness due to the skin effect. The models have been compared to experimental results comprising magneto-optical investigations and fluxmetric measurements.  A novel broadband power loss and permeability model valid for amorphous/nanocrystalline tapes from DC to 1 GHz was developed using the Maxwell and Landau-Lifshitz equations.

Two-dimensional magnetisation and power losses:

One goal of the project is to study the magnetisation process in NO materials used in rotating electrical machines under 2D fields, excited using a 3-phase magnetiser up to saturation polarisation, and to develop loss models based on the statistical theory of losses. A three-phase vector magnetiser was used to compare fluxmetric and thermometric measurement methods on NO 0.35 mm thick laminations from 5 Hz to 400 Hz in the polarisation range 0.1 T < Jp < 1.7 T using the  field-metric technique and 1.6T < Jp < 1.9T using the thermo-metric method. An overlap of the two sets was observed in the 1.6T < Jp < 1.7 T interval. The measurements have now been repeated on an NO 0.3 mm sample under rotational and elliptical flux (with an axes aspect ratio = 0.5) from 5 Hz to 400 Hz in the polarisation range 0.25 T < Jp < 1.5 T using the field-metric technique and 1.4T < Jp < 1.8T using the thermo-metric method and an overlap of the two datasets was observed in the 1.4 < Jp < 1.5 T interval. These results are used to better understand and emulate the two-dimensional flux loci in the non-oriented steel laminations in the stator core of a rotating electrical machine.

A study is being completed on the role of sample geometry on the magnetisation curve and losses in high permeability FeSi GO transformer laminations cut along directions from rolling to transverse, from DC up to 400 Hz.  In the first part of the project, magnetic hysteresis loop and losses in were investigated in GO FeSi 0.3 mm under DC and AC (1 Hz - 200 Hz) regime. The experimental data was collected both using an Epstein frame and a non-standard single sheet/strip tester. A phenomenological loss prediction method was devised, based on the behaviour of hysteresis loops and energy losses independently measured under sinusoidal induction in the RD- and TD-cut Epstein strips. A peer-reviewed open access journal article on anisotropy of losses in grain oriented Fe-Si was published in 2021 based on the results achieved. A new set of FeSi GO 0.18 mm samples is being now prepared for further investigations  

Impact

The HEFMAG website was created at https://hefmag.inrim.it/, and a collaborative platform is now available at https://github.com/HEFMAG with an open access area and a new community “Metrology of magnetic losses in electrical steel sheets for high-efficiency energy conversion”.was started on Zenodo, where a project-related dataset sample is available. Consortium members have presented five contributions related to the project at four different international conferences, WMM’20, AIM 2020, Intermag 2021 and 1&2DM, and at a seminar organised by the UK Magnetic Society. Five training activities have already been held, four on loss measurements with Epstein and SST equipment or magneto-optics, three related to new personnel at NMIs, one at a project partner, and one for PhD students on magnetism in materials and measurements.

A stakeholder committee with 19 members was formed and a first meeting was organised in October 2020. Samples for Epstein and SST measurements were kindly made available by selected stakeholders. An email update on the project activities was circulated in April 2021. A wide number of stakeholders declared interest in participating in activities related to the round robins and a second off-line meeting was held in December 2021 to better identify stakeholder needs and interests and useful feedback was collected though a questionnaire. Reference samples will be available to the stakeholders as soon as the experimental activities of the partners are concluded and a preliminary data analysis carried out. Follow-up activities will continue through the project.

The project partners have already provided several input towards updates of existing documentary standards on measurements performed on magnetic materials through engagement with BSI, the standardisation body of the United Kingdom, through activities of CEI, the Italian equivalent of IEC, and through IEC TC 68. 

Impact on industrial and other user communities

The outcomes of this project will benefit the power generation and supply industry; the transport sector; the machinery and metal products industries, leading to an increased energy conversion efficiency in utility transformers, high performance generators (i.e. wind and hydroelectric) and motors including aerospace, electric cars, scooters and bicycles where high efficiency is required. Novel smart-grid power distribution networks driven by renewable sources (wind, solar) as well as high power railway and aircraft/drone engines will require small size solid-state transformers operating at frequencies for which no validated measurement standards yet exist. To date, electrical machine designers rely on inadequate magnetic hysteresis and loss data obtained under conditions that do not match real world conditions. New calibration and measurement services will be established and offered to relevant European industries, stakeholders and end users. Project results disseminated through updated and new standards, publications, and good practice guides will lead to increased confidence in the use of experimental data for modelling of hysteresis and loss with noticeable improvements in electrical machine design.

Impact on the metrology and scientific communities

New and extended magnetic loss measurement procedures developed in the project will be made available to the metrology and scientific communities through the project website and data repository, through reports to EURAMET TC-EM, CIPM CCEM, and the relevant IEC committees, and through good practice guides and open-access scientific publications. Reference samples produced as a result of the round robin comparisons will also be available for calibrations and thus will immediately support improved magnetic loss metrology research and development. New and extended metrology infrastructure for loss measurements at high temperatures developed and established at the NMIs participating in the project will be made available to the metrological and scientific community. The project also addresses magneto optical surface characterisation under dynamic and elevated temperature conditions that have not been performed on electrical steel to date, as well as studies of the AC magnetic field penetration affected by the skin effect and by local structural defects in a wide frequency range from 50 Hz-10 kHz. The results obtained will provide parameters such as domain width and domain densities and additional information about flux penetration depths that will be used within the metrology and R&D communities as input parameters for extended magnetic modelling to improve the reliability and effectiveness of the loss and hysteresis models.

Impact on relevant standards

This project will support the implementation of the Ecodesign Directive 2009/125/EC, which provides consistent EU-wide rules for improving the environmental performance of products by setting out minimum mandatory requirements for energy efficiency, through the development and dissemination of state-of-the-art loss measurement and hysteresis modelling techniques. The consortium will promote the uptake of the project’s results within the standardisation community through the publication of good practice guides directed to end users. This project is directly providing input to the IEC TC 68 “Magnetic alloys and steels” for discussion and evolution of the current standards.

Longer-term economic, social and environmental impacts

Europe, with 500 production sites spread across 23 EU countries, is the second largest producer of steel in the world after China. Steel-making is the third largest EU industry, and closely linked to many downstream industries such as construction, automotive, electronics, mechanical and electrical engineering, where magnetic grade steel is used for the production and transformation of almost all of the distributed electric power, for industrial and household motors and now increasingly for the transport sector. The current global magnetic steel market has a value exceeding 20 billion Euros per year and most soft magnetic steel production is in the EU and Asia. Magnetic steel is used in Europe by more than 2500 transformer and electric motor manufacturers and producers. The state-of-the-art and metrologically validated measurement techniques and associated guidance developed in the project will support the characterisation of novel and more energy-efficient industrial steel products, helping Europe to maintain and expand its expertise and leadership in the production of special steel.

People’s health can be affected by (local) emissions from power plants, district heating and local residential heating systems, transport and industry. Electricity and heat generated by these facilities lead to increased air pollution such as NOx, SO2, small particulate matters (PM2.5) and CO2. The European Environmental Agency estimated that there were 403,000 deaths related to PM2.5 and 72,000 deaths related to NOx in 2012. By reducing energy consumption and implementing energy efficiency policies targeting industrial processes, some of this air pollution can be avoided including emissions of PM2.5.

The cumulative energy savings associated with the implementation of the Ecodesign directive to be achieved between 2009 and 2020 were estimated to reach 2035 TWh, with additional energy savings of 100 TWh per year by 2030. The outcomes of this project, which promotes more accurate and efficient magnetic steel testing measurement methods, are expected to be used in the power generation and supply industry; the transport and aerospace sector; and the machinery and metal products industries, leading to an overall improved energy conversion efficiency. Additional energy savings connected to the design and construction of higher efficiency electric motors, transformers and power electronics devices, will also contribute to reaching the EU 32.5 % efficiency target for 2030, defined by the EC Energy Efficiency Directive 2012/27/EU (amended 2018/2002).

List of publications

[1] Ragusa, C., Appino, C., Ferrara, E. and de la Barrière, O., „Anistropy of losses in grain oriented Fe-Si“, AIP Advances 11 (2021) 115208. https://doi.org/10.1063/5.0066131

[2] O. de la Barrière, E. Ferrara, A. Magni, A. Sola, C. Ragusa, C. Appino, and F. Fiorillo. Wideband magnetic losses and their interpretation in HGO steel sheets. Journal of Magnetism and Magnetic Materials Volume 565, 1 January 2023, 170214. https://doi.org/10.1016/j.jmmm.2022.170214.

This list is also available here: https://www.euramet.org/repository/research-publications-repository-link/ 

Project start date and duration:01 September 2021, 36 months

Coordinator: Massimo Pasquale, INRIM             Tel: +39-011-3919820                  E-mail: m.pasquale@inrim.it

Project website: https://hefmag.inrim.it/

Internal Funded Partners:

1.  INRIM, Italy

2.  CMI, Czech Republic

3.  NPL, United Kingdom

4.  PTB, Germany

5.  TUBITAK, Turkey

External Funded Partners:

6.  CNRS, France

7.  IFW Dresden, Germany

8.  INNOVENT, Germany

9.  POLITO, Italy

10. UNOTT, United Kingdom