Magnetics Business & Technology - Summer 2012 - (Page 10)

FEATURE ARTICLE By haRRie Buswell, ceo • Buswell eneRGy llc The Process of Developing and Testing a New Transformer The development of a new transformer has embodied both old and new. Our current prototype model is a near toroid with eight sectors of magnetic components spread as evenly as possible around the electrical to achieve homogeneity, symmetry and an encompassing of the electrical with magnetics. The sectors are wound up with wire. Wire allows some lessening of classical sheet magnetic constraints. Not only can the geometry constraints be lessened allowing more flexibility of design also the generation of eddy currents is lessened. The prototype in Figure 1 is a 10 KVA oil-immersed distribution transformer. A design that scales well across distribution transformer sizes it is currently undergoing accelerated aging testing at Tennessee Tech EE department. While a nice looking prototype with several promising operating parameters it just isn’t “right”. The magnetic material in a wire form factor does not perform as well as conventional high-grade grain oriented sheet material. The material, the part that I naively thought would be the easier turned out not to be. Achieving a suitable and competitive magnetic Figure 1. Prototype 10 KVA Transformer material has become the greatest challenge. Looking for a Suitable Material The material I had thought would be easy wasn’t easy to find. The search led around the nation and across the world with some interesting connections and possibilities. We found no magnetic material of a wire form factor that could perform as well as high quality sheet material. We partnered up with Bekaert Wire and Oak Ridge National Laboratory and began to search more deeply. The searching changed from that of looking for a ready-made material to that of concentrating on development of a material with associated necessary processes. The material must perform well magnetically (good soft magnetic qualities) and also must be suitable electrically. Suitable electrically means as high a resistivity as practicable to minimize internal eddy current production and with a high enough surface insulation resistance to suppress the generation of eddy currents from adjacent contact wire to wire. Two Worlds of Testing Searching for a material means testing. Deep testing of material involves expensive and sophisticated equipment such as hysteresigraphs for BH plots giving much information on each plot and SQUID (Superconducting Quantum Interference Detector) testing, which is one of the most sensitive tests in the world. Ongoing testing need only reference in some way back to these tests. The testing suitability of new materials here involves the two testing importances; magnetics and electrical. The testing must accommodate both the magnetic needs and the electrical needs of the magnetics for devices made with a wire form factor magnetic material. The testing for a material whether found or developed entails testing magnetically (saturation intensity high, relative permeability high, coercivity low, rententivity low) and electrical (electrical resistance high.and surface insulation resistance with a much higher resistance than the internal resistance). By necessity the testing resolves into two sorts of testing: large sample testing and small sample testing. Large sample means that there is sufficient material to make up a device and test it, or to make up a representative part of a device and test it. This also means that more time and care is taken to prepare the large sample components whether a complete unit, a portion or a coil of wire to represent a working component. Small sample testing allows small pieces to be tested relatively by comparing sample to sample and by comparing sample to reference samples. Within the search process for a promising combination of chemistry and process, the rapid testing of small samples can discriminate better or worse qualities. From this perspective the two worlds of testing are bifurcated into large sample testing and small sample testing. Established Test Protocols ASTM has long established tests for the magnetic qualities and for the surface insulation resistance. ASTM A717, A937, A347, and A976 are among the standards that deal with sheet material testing. Classical testing is accomplished with a Franklin Tester (surface insulation resistance) and the Epstein Frame Tests (soft magnetic qualities with both single lamination and laminate stacks). Other standards around the world have similar rules and protocols. The Epstein Frame approaches and the Franklin Testers are not so appropriate for wire testing. Of course the first considerations are to modify the tests to accommodate wire form factor. However, some conditions of sheet testing are inherently more difficult than wire testing. Rather than try to adjust already difficult tests this seems a good time to explore other approaches. Large and Small Sample Testing Large samples of wire magnetic material can be tested as simple coils, as sector components, and of course complete transformers, each progression taking additional care, expense and time. The testing results in Watts loss accounts for both the soft magnetics and the electrical resistivities. Turns of an electrical wire of known resistivity are installed around made-up coil or sector and then currents, voltages and wattages are established with a power analyzer. But there is another test available that can be accomplished www.MagneticsMagazine.com 10 Magnetics Business & Technology • Summer 2012 http://www.MagneticsMagazine.com

Table of Contents for the Digital Edition of Magnetics Business & Technology - Summer 2012

Magnetics Business & Technology - Summer 2012
Editor's Choice
Injection Molded Magnets for Electrical Machines
The Process of Developing and Testing a New Transformer
Rare Earths & Corporate Social Responsibility
Research & Development
RE-use, RE-duce, RE-cycle, RE-place
Magnets • Materials • Measurement
Application • Component Developments
Industry News
Rare Earth Crisis Dissected: Securing the Future
Marketplace
Advertising Index
Spontaneous Thoughts: The End of Axial Pressing?

Magnetics Business & Technology - Summer 2012