Teoriya û Zanînên Cûrê Bihêranî

Guherandara di navbera core transformer de herêmekirina emf di core de xasî li ser faraday law û lenz law, eddy current di core de hatek çalak kirin wêgirtina di navbera figure de. Herêmekirina B(t) ji bo i(t) di winding de, eddy current ieddy di core de hatek çalak kirin.

Guhertina ji bo eddy currents di navbera formula de hatek bike :

Yê ku ke = constant depends on the size and inversely proportional to the resistivity of material,
f = frequency of the excitation source,
Bm = peak value of the magnetic field and
τ = thickness of the material.

Formula di navbera jêrîn hatek bike ku guhertina eddy current bi density flux, frequency û thickness materiala di navbera materiala reng û proporsionala be.

• Bi rêya herêmekirina guhertinên eddy current di transformer core di navbera stacking thin plates called laminations together û har plate varnished û insulated bike ku flow eddy current confined to a very small cross section area of each plate û insulated from other plates. Wêjê flow of current decreases to minimum. Veya şo biyayî ye :

• Bi rêya zêdetkirina resistivity materiala cold rolled grain oriented, CRGO grade steel used as core of transformer.

Properties of Eddy Currents

• Only inside the conducting materials.

• These are distorted by defects such as cracks, corrosion, edges etc.

• Eddy currents attenuate with depth with highest intensity present at the surface.

Application of Eddy Current

Magnetic Levitation: It is a repulsive type of levitation finds application in modern high speed Maglev trains to provide frictionless transportation. Changing magnetic flux produced by a superconducting magnet placed on the moving train produces eddy currents on the stationary conducting sheet over which train levitates. The eddy currents interact with the magnetic field to produces forces of levitation.

Hyperthermia Cancer Treatment: Eddy current heating used for tissue heating. Eddy currents induced in the conducting tubings by proximal wire windings connected to a capacitor to form a tank circuit which is connected to a radio frequency source.

Eddy Current Braking: Kinetic energy converted into heat due to eddy current losses finds numerous applications in industry :

• Braking of trains.

• Braking of a roller coaster.

• Electric saw or drill for its emergency shut-off.

Induction Heating: It is the process of electrically heating a conducting body by inducing eddy currents in it using high frequency electromagnet. Its main applications are induction cooking, induction furnace used to heat metals to their melting point, welding, brazing etc.

Eddy Current Adjustable Speed Drives: With the help of feedback controller an eddy current coupled speed drive can be achieved. It finds applications in metal forming, conveyors, plastic processing etc.

Metal Detectors: It detects present of metals inside rocks, soils etc. with the help of eddy current induction in the metal if present.

Data Processing Applications: Eddy current non destructive testing used in investigating composition and hardness of metal structures.

Speedometer and Proximity Sensing Applications

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