A great capacitor bank for a great magnetizer
Magnetism is used in many industrial applications, with increasingly sophisticated and better performing magnetic materials that guarantee high performance with reduced volumes and costs. The magnetization procedure can be performed with different methods in accordance with the magnetic substance type, the magnet shape/dimension, and the desired performance. A much used method is the “capacitor discharge,” which can request circuits able to develop the highest currents. The high remanence magnetic materials (the remanence is the iron magnetic material magnetization value with external magnetic field null), which will have an important role in electric vehicle development, turn out to magnetize only by applying high magnetic fields and with a well determined trend. An important Japanese university is performing some studies to realize high magnetic impulses, to magnetize permanent magnets in Nd – Dy – Fe – B (neodymium-dysprosium-iron-boron) with a special system that can generate fields up to 33T with a duration of 10ms, or 20T for 300ms. To have an idea of the strength, the Earth magnetic field is about 10-5 T, the field generated from a large industrial magnet is 0.01T.
The circuit used is shown in the figure. The system “heart” is the capacitive bank, which in this case must be able to emit an extremely high current with a well determined trend, with the aim to obtain the magnetization curve, the desired remanence (that must be > 1T), and the coercivity (10T). The coercivity is the inverse magnetic field intensity that it is necessary to apply to a material to cancel its magnetization, and it is a value that shows the quality of a permanent magnet. High coercivity material is called “magnetically hard.”
ICAR has supplied the capacitors of “energy storage/rapid discharge” to create the capacitive banks. Two capacitor typologies have been supplied, each of which can store 90kJ, either with a capacity of 50µF at 60kVdc or with capacity of 312.5µF at 24kVdc. The total capacity installed in the system is equal to about 0.1F, which is a very high value.
- Achieving desired magnetization curve