Author:
Reported by Cliff Keys, Editorial Director, Editor-in-Chief, Power Systems Design
Date
11/26/2010
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I had the opportunity to visit MAGNETEC's extremely busy booth and speak with Helmut Doenges, the company's Director of Marketing. The company holds a worldwide leading position in the development and production of high grade tape wound ring cores made of soft magnetic alloys MAGNEPERM® and NANOPERM®. The main application areas are mains-independent (mechanical) earth leakage circuit breakers (ELCB) and the full range of power electronics/EMI. The applications serviced by MAGNETEC cover all industrial power supplies and variable speed drives (frequency converters) as well as the fast growing market for renewable energy such as PV solar inverters or windmill installations.
The new Cool Blue range completes MAGNETEC's series of high performance toroids made from the nano-crystalline material NANOPERM. Available are cores up to 500mm outer diameter and several space saving stadium-shaped variants. The cores in this new series feature significantly improved high frequency performance due to a permeability level several times higher than any kind of ferrite. In Europe, Cool Blue cores are being used increasingly to reduce damaging bearing currents of modern inverter systems of the latest generation (doubly fed induction generators (DFIG) IGBT technology) from approx. 500kW up to about 5MW. As a consequence of those parasitic currents, the bearings corrugate followed by electrical breakdown of the lubrication which causes an early failure and standstill of the whole motor. The same effect occurs in modern wind energy generators, even though the direction of the energy flow is reversed in this application. Some of the leading European Wind Turbine manufacturers have successfully designed-in the new Cool Blueâ cores recently because it is technically the most effective and proven solution to a severe problem and provides the best value for money. The Cool Blueâ solution is significantly cheaper than isolating hybrid bearings. With these high-tech cores not only are the over-voltage peaks at the winding terminals significantly reduced, but also the asymmetrical EMI currents which are generated by parasitic capacities of the interconnecting cables and the motor/generator itself. In order to achieve an efficient reduction of those destructive effects, several nano-crystalline cores of suitable geometry have to be put commonly over the connector cables each in the DC-link and/or at the inverter output. In this configuration, the cores operate as common-mode chokes. This method significantly increases the service life of the generator bearings and thus significantly reduces maintenance costs and costly standstill periods. Summary of advantages of Cool Blue cores:
Electronic Motor Protection relays are getting increasingly popular all over the world. They become considerably simpler and cheaper as a result of the use of newly developed current sensor systems like high reliable and precision current transformers. Current transformers with cores made of highly permeable soft magnetic alloys are the best solution for a protection relays to sense motor current in a reliable and safety way, because the increase in motor operating temperature reduces the winding insulation life, accurate thermal overload protection is critical. MAGNETEC cores offer a unique combination of high-permeability and high-linearity for related current transformers in electronic motor protection relays. Using the soft magnetic alloys MAGNEPERM® and NANOPERM® will benefit in low amplitude deviation with high-linearity phase curves are the main advantages of the magnetic cores. Current-transformer-based motor protection relays deliver outstanding advantages in case of higher sensitivity, years of reliable functioning and maximum electrical safety in comparison to e.g. standard thermal overload relays. The use of MAGNETEC cores for current transformers in motor protection relay will extend the lifetime of a motor, optimised motor size, simplified maintenance work and protection of drives from mechanical damage.
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In the past, nanocrystalline cores could not be used in applications with significant DC preload because they saturate early due to their high permeability level (>18.000), which provided an advantage only in non DC applications. MAGNETEC offers high saturation cores which enter into a low permeability range of typically 2.000-8.000 which have not been available until now. These cores are highly advantageous in EMC filters for applications with a high level of asymmetric interference current (e.g. inverter drives) with regard to build volume and/or attenua¬tion performance compared to the traditional Ferrite materials. The reason is, that the nanocrystalline core material NANOPERM LM offers three times as much saturation flux density at the same level of permeability. Another important application is found in precision Current transformers for household energy meters which are currently equipped with very expensive cobalt-amorphous cores. Here, the new material offers a significant cost advantage. New current transformers for use in electronic watt-hour meters In addition to MAGNETEC's product line of soft magnetic cores with nanocrystalline material, the company presented the new series of current transformers based on NANOPERM®LM. Electronic watt-hour meters are increasing worldwide for new electric grid infrastructure and changes in energy consumer regulations. More and more current transformers will be used to meet the requirements of IEC or ANSI standards. The market offers a variety of solutions. Current transformers deliver huge advantages in comparison to the shunt and Rogowski methods in terms of dynamics, robustness and long-term stability. The new current transformers are working in the range from 20A to 160A and based on nano-crystalline cores from the alloy family NANOPERM®LM. The outstanding performance produces a highly linear phase error which can easily compensated by the use of modern meter-ICs. Furthermore, a full dc-tolerance based on EN 62053-21 standard is a main feature of this series. The new current transformers offer unique advantages for modern electronic watt-hour meters in terms of true and reliable energy measurement. They exceed in many cases the requirements of the meter industry for reasonable prices. For electronic watt-hour meters, where manipulation of measuring accuracy should be protected against external magnetic fields, MAGNETEC also offers new shielded current transformers. Higher efficiency of PV inverters with nanocrystalline EMC filter chokes One of the most important goals within the solar voltaic Industry is to further increase the efficiency of the complex process of energy conversion. Every single fraction of a percent is welcome - although more than 90% are already state-of-the art for modern DC/AC converters. Following this target, more and more producers of inverters are currently replacing standard components by high tech solutions providing the best possible electrical efficiency. An important example is the choke in EMI filters. Nanocrystalline cores offer a permeability five times higher than ferrites which results in significantly smaller build volume and - as a consequence - the copper resistance is reduced significantly, typically by a colossal 50 percent. www.magnetec.de
