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Magnetic Circuit - Electrical Machines Transformers (Formula Notes)

Learn Magnetic Circuits and how magnets work in simple terms. Explore the basics of magnetic fields and how they influence electrical devices like transformers.
authorImageRanvijay Singh20 Nov, 2023
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Magnetic Circuit

Magnetic Circuit Important Terms and Definitions

Magnetic Circuit Magnetic circuit is a closed path in which magnetic flux is set up either by permanent magnets or electromagnets. Ferromagnetic materials are used in the core that provides low reluctance path for flux. Knowledge of different terms of magnetic circuits are necessary to understand electrical machines.

Magnetomotive Force (MMF)

It is responsible for set-up of magnetic flux in the circuit. Magnetomotive Force Its unit is Ampere-turns. It is analogous to electromotive force in Electric circuit.

Magnetic Field Intensity

It is defined as MMF per unit length. Magnetic Field Intensity

Magnetic Flux

It is defined as the total number of magnetic field lines passing through an area. Its unit is Weber. It is analogous to current in electric circuit. Magnetic Flux

Magnetic Flux Density

Magnetic flux per unit area of the core is called magnetic flux density. It’s unit is Tesla (T) or Wb/m 2 . Magnetic Flux Density

Reluctance

The opposition offered to the magnetic flux in the core is called reluctance. It’s unit is (Henry) –1 or AT/Wb . Reluctance The reciprocal of reluctance is called Permeance . Reluctance is analogous to resistance in electric circuit.

Permeability

It is the ability of a magnetic material to allow magnetic field lines to pass through it.

Inductance

It is the property of a coil to oppose change in electric current that flows through it. Its unit is Henry . Inductance
Sl. No. Electric Circuit Magnetic Circuit
1. It is a closed path for electric current. It is a closed path for magnetic flux.
2. EMF drives the circuit. MMF drives the circuit.
3. Current Electric Circuit Flux Magnetic Circuit
4. Resistance Electric Circuit Reluctance Magnetic Circuit
5. Condutance Electric Circuit Permeance Magnetic Circuit
6. Current density Electric Circuit Flux density Magnetic Circuit
7. In electric circuit, electric current flows. In magnetic circuit, magnetic flux is set up. It does not flow.
8. Electric current does not flow through air. Magnetic flux is established in air also.
9. Energy is continously required for maintaining current in electric circuit. Energy is only required to produce magnetic flux. It is not required to maintain it.
Note: In a closed magnetic path, net reluctance is the sum of all the reluctances encountered in the path.

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