Inside the next generation of magnetic materials What options should you be considering as permanent magnet sourcing gets tough? CWIEME Berlin 2013 4 June, 12:00-12:45 Dr. Sandra Eriksson Associate professor/senior lecturer Division of Electricity Uppsala University sandra.eriksson@angstrom.uu.se
Today s presentation Introduction to rare earth metal free PMs Neodymium price development Material properties and comparison Machine design Ex 1: Comparative study Ferrite/Nd generator Ex 2: Ferrite wave power linear generator Conclusions Questions
Today s presentation
Renewable energy research at division for electricity, Uppsala. Wave, wind and water current power plants with direct driven permanent magnet (PM) generators. Applied research. Several spin-off companies. Photo: Division of Electricity
*Source: China reshapes role in rare earths, could be importer by 2014, REUTERS.com, 10 th of July 2012. Introduction: Rare earth metal free permanent magnets Why do we want rare earth metal free permanent magnets? Price development Environmental aspects Politically unstable Availability 95% of resources in China China could be a net importer of rare-earth metals in 2014*. Similar scenario for Neodymium, Praseodymium, Dysprosium etc.
Introduction: Rare earth metal free generators Optional technology Electromagnets loosing the benefits of using permanent magnets - rotor losses - electrification - maintenance etc. Reluctance machine could be an option for some applications.
Introduction: Rare earth metal free permanent magnets Optional materials Old materials: Modern materials: New materials: Ferrites SmCo NewMag SmCo contains Samarium a rare earth metal. Similar properties as NdFeB but more expensive. Dysprosium free option exists.
Neodymium price development Nd metal price increased more than 1000% from Aug-09 to Aug-11! May-13: 61 EUR/kg.
Magnetic properties Remanence, Br, is the remanining magnetic flux density in a permanent magnet. Normal coercivity, Hcn, the external field for which the net magnetic flux density from the PM is zero. Intrinsic coercivity, Hci, the external field for which the magnet is permanently demagnetized. Energy product, BH max, the energy stored in the PM.
Material properties Material strength: The mounting procedure, when the magnets are placed in the generator rotor, normally represents the most challenging part for the material. Corrosion protection: The rotor geometry and the material will affect the need for protective coating.
Material properties Considerations for alternative PM materials Magnetic properties Energy product (kj/m 3 ) Remanence (T) Normal and intrinsic coercivity (ka/m) Electrical properties Electric conductivity (S/m) Mechanical properties Density (kg/m 3 ) Material strength Material properties Corrosion protection
Magnetic properties Property NdFeB Ferrite NewMat Type N40H Y40 NM* Br (T) 1.29 0.45 ~1.2 Hcn (ka/m) 915 342 ~200 Hci (ka/m) 1353 350 ~250 En. prod. (kj/m 3 ) 318 39.7 ~100-150 *Target values for a supposed new material, NOT existing today.
Material properties Property NdFeB Ferrite NewMat Type N40H Y40 NM Material strength Ok Brittle - Corrosion prot. Bad* Good - El. res. (μωcm) 140 1e10 - Density (kg/m 3 ) 7700 5000 ~7500 *Needs protective coating
Material comparison and cost Property NdFeB Ferrite NewMat Type N40H Y40 NM* En. prod. (kj/m 3 ) 318 39.7 ~100-150 Density (kg/m 3 ) 7700 5000 ~7500 En. Dens. (J/kg) 41.3 7.9 ~13-20 Rel. req. mass 1 5.2 ~2-3 PM price** ( /kg) 25 1 - Relative energy price 1 0.2 - *Target values for a supposed new material, NOT existing today. **Based on quotations for finished magnets.
Machine design Machine properties that affect the PM choice Volume or weight constrains Motor or generator Rotational speed Electrical frequency Operating temperature and cooling system Current peaks Current level Harmonic content Short-circuit currents Electrical system and control
PM rotor design If stator steel is used: B in Airgap of 0.8-1.0 T Low Br Field reinforcement needed Low Hci Field protection needed
Alternative rotor designs
NdFeB generator design NdFeB: High Br, high Hci No flux reinforcement or extra protection needed: Radially magnetized, surface mounted PMs. If rectangular magnets are used, no possibility is given to shape field with pole.
Ferrite generator design Ferrite: Low Br, low Hci Need flux reinforcement and protection: Tangentially magnetized and buried PMs. Approx. 5.2 times more PM mass than for NdFeB. Possibility to shape field with pole and use rectangular PMs.
*A supposed new material, NOT existing today. NewMat generator design NewMat*: High Br, low Hci No reinforcement, but protection needed: Radially magnetized and buried PMs. Approx. 2-3 times more PM mass than for NdFeB. Possibility to shape field with pole and use rectangular PMs.
Design issues for a ferrite rotor Achieve high magnetic flux density in the airgap Mounting of PMs Increased mass Affects supporting material and bearings Affects stability and control Affects shaft vibration eigen frequency Risk for demagnetization A larger diameter might be preferable
Ex 1: NdFeB vs. ferrite rotor Comparative study to see if a generator with exactly the same electromagnetic properties and an identical stator could be designed. A generator requiring large overload capacity Large amount of PMs needed. S. Eriksson, H. Bernhoff, Rotor Design for PM Generators Reflecting the Unstable Neodymium Price, Electrical Machines (ICEM), 2012 XXth International Conference on, pp.1419-1423, 2-5 Sept. 2012.
Ex 1: NdFeB vs. ferrite rotor FEM simulations. Magnetic flux density (T). S. Eriksson, H. Bernhoff, Rotor Design for PM Generators Reflecting the Unstable Neodymium Price, Electrical Machines (ICEM), 2012 XXth International Conference on, pp.1419-1423, 2-5 Sept. 2012.
Ex 1: NdFeB vs. ferrite rotor Electromagnetic characteristic NdFeB Ferrite Active power (kw) 225 225 Load L-L voltage (V) rms 793 793 Current (A) rms 164 164 Electrical frequency (Hz) 9.9 9.9 Rotational speed (r/min) 33 33 Torque (knm) 65 65 Maximum torque (knm) 200 178 Cogging (% of rated torque) 1.8 1.3 Electrical efficiency (%) 96.6 96.6 Stator copper losses (kw) 5.4 5.4 Stator iron losses (kw) 2.4 2.4 Load angle ( ) 9.6 9.3 Airgap force (MN/m 2 ) 0.18 0.20 S. Eriksson, H. Bernhoff, Rotor Design for PM Generators Reflecting the Unstable Neodymium Price, Electrical Machines (ICEM), 2012 XXth International Conference on, pp.1419-1423, 2-5 Sept. 2012.
Ex 1: NdFeB vs. ferrite rotor Property NdFeB Ferrite PM mass (kg) 536 4789 Approx. rotor weight (t) 3.3 10.8 Large weight difference: PM mass 8.6 times higher for ferrites. Rotor weight 3.3 times higher for ferrites. Study made with Y30 ferrite. Y30: Energy product 28.0 kj/m 3 = 6.0 J/kg Y40: Energy product 39.7 kj/m 3 = 7.9 J/kg S. Eriksson, H. Bernhoff, Rotor Design for PM Generators Reflecting the Unstable Neodymium Price, Electrical Machines (ICEM), 2012 XXth International Conference on, pp.1419-1423, 2-5 Sept. 2012.
Ex 1: Comparative study It is possible to design a ferrite PM machine with the same electromagnetic properties as an NdFeB machine. For designs where generator weight is less of an issue, ferrites might be a viable option. An interchangeable rotor can be an option making it easier to predict the price. S. Eriksson, H. Bernhoff, Rotor Design for PM Generators Reflecting the Unstable Neodymium Price, Electrical Machines (ICEM), 2012 XXth International Conference on, pp.1419-1423, 2-5 Sept. 2012.
Ex 2: Ferrite generator for a wave power plant Buoy and line Linear generator Pull-back springs (or large mass) Actually beneficial with large translator weight!
Ex 2: Ferrite linear generator
Ex 2: Ferrite translator Mounting of the first linear ferrite translator for wave power. Installed March-2013.
Conclusions It is important to find alternatives to Neodymium (Environmental, price and availability reasons). Ferrites are a viable option if increased weight and lower coercivity are acceptable. Rare earth metal free new materials are currently being developed. A positive future outlook for rare earth metal free permanent magnet electrical machines.
Conclusions: What to do next? Consider if ferrites can be an option for your application. Wait out the new materials, both US and European attempts are currently being made to find new rare earth metal free permanent magnet materials. Electromagnets could of course be an option.
Thank You for the attention! Questions?