Magnetic Circuits and Transformers

# Magnetic Circuits and Transformers - Magnetic Circuits and...

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Magnetic Circuits and Transformers Sattar Hussain [email protected]

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1- Magnetic Field It is customary to represent the magnetic field by means of lines of forces that can be traced as a closed loops exiting at magnetic north pole and entering at magnetic south pole. These line are called flux lines . The flux lines take the least resistance path; that is, they are easier to set up in an iron medium than in the air.
The total number of flux lines is referred to as magnetic flux ϕ measured in weber (Wb) . The density of flux lines per unit of cross-sectional area perpendicular to the direction of the flux lines is called flux density, B , measured in Wb/m 2 or Tesla (T). The flux ϕ is then defined as the integral of the flux density over some surface area, A . If the flux is uniform over the cross sectional area A , then: = A BdA φ A B . = φ

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The magnetic resistance that tends to oppose the establishment of magnetic flux lines is referred to as reluctance, . Reluctance of iron bar is much less than air reluctance. Hence, the iron bar is an easier path than air for flux lines. 2- Magnetic Field Produced by Currents A conductor carrying an electric current I exhibits a magnetic field in the space surrounding it.
The magnetic field is stronger near the conductor and decreases farther a way from it. The magnetic flux, ϕ , increases when the current , I increases. The direction of flux lines is determined by Ampere’s right- hand rule (RHR) . It states: when the thumb points to the current direction, the fingers point to the direction of magnetic field lines.

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