State the advantages and disadvantages of alloying steel with silicon for use as magnetic materials in transformer and electric machines.
Extensive utilize, is made of iron-silicon alloy termed as silicon steel for relatively strong alternating magnetic fields usually used in transformers, reactors, electrical rotating machines, relays and electromagnets. Silicon sharply raises the electrical resistivity of iron therefore decreasing the iron losses because of eddy currents. This increases the permeability at low and moderate flux densities but reduces this at high densities. Addition of silicon to iron decreases the hysteresis loss. The magneto striction effect is reduced also. A, steel with more than 5 percent silicon may be too hard and brittle to be simply workable. The introduction of silicon in steel was a significant development. Previously, iron was used as the core material in the form of sheets, the material slowly deteriorated because of repeated cooling and heating. This difficulty is overcome using silicon sheet steel like core material. High silicon sheet steel along with silicon of about 4 percent is used in magnetic circuits of power transformers that operate at flux densities of about 1 Wb/m2. The cores of rotating electrical machines are slotted along with the teeth having small cross sectional areas. The flux density in teeth is higher, of the order of 1Wb/m2. To acquire high flux density in the case of high silicon steel, the magnetising current essential is very large. Also punching slots in high silicon steel would be not easy because this is harder and more brittle.