Eddy currents are currents that circulate in conductors like swirling eddies (a whirlpool) in a stream. They are induced by changing magnetic fields and flow in closed loops, perpendicular to the plane of the magnetic field.
They arise when a conductor moves through a magnetic field, or when the magnetic field surrounding a stationary conductor is varying. Summarising, we can say that anything which results in the conductor experiencing a change in the intensity or direction of a magnetic field produces eddy currents.
How to minimize the eddy current?
We can minimise the eddy current by the following methods:
- The resistance of the core should be increased.
- In transformers, the thin sheets of steel in the core should be insulated from each other by a thin layer of varnish.
- As the laminations are thin, they will have relatively high resistance.
- The planes of these sheets are placed perpendicular to the direction of the current that would be set up by the induced emf. The planes of these sheets are arranged parallel to the magnetic fields so that they can cut across the eddy current paths.
- Large resistances between the sheets confines the eddy currents to the thin sheets. Each lamination sheet will have an eddy current circulates within it. Tiny eddy currents still exist, but only within each thin sheet, so are greatly reduced.
- The sum of individual eddy currents of all the laminations are very less compared to that of using a single solid iron core.
Uses of eddy current
- One of the most common electromagnetic NDT methods is to use eddy currents to see whether a material or surface has any discontinuities, fractures, or faults without harming the material.
- When an eddy current comes into close contact with a conductive or magnetic material, electromagnetic damping is automatically produced. When an eddy current interacts with another magnetic field, it causes electromagnetic damping.