What is Eddy Current Loss?-Definition and Expression

Eddy Current Loss

When magnetic material comes under a magnetic field generated by alternating current, an emf induce in the core material according to Faraday’s Law of Electromagnetic induction. The magnetic material has electrical conducting property and the induced emf in the material causes current to flow in the magnetic material. The current circulates within the material. And, the circulating current caused by induced EMF is called Eddy Currents. The heat loss caused by eddy currents in the magnetic material is called eddy current loss.

The circulating current caused by induced EMF is Eddy Currents. The heat loss caused by eddy currents is eddy current loss.

The other loss in the magnetic material is hysteresis loss. The combined losses-eddy current and hysteresis losses- are called iron loss, magnetic loss, and constant loss.

The eddy current flowing mechanism is shown in the figure above. When the alternating current flows through the coil, it set up magnetic flux in the magnetic material. The flux also links to the core material and induces EMF at the various points of the core. The potential difference causes closed-loop circulating current in the core. The circulating current is called Eddy Current. 

The magnitude of the eddy current depends on ;

  • Resistance of current path
  • Frequency of supply source
  • The magnitude of flux density
  • The thickness of the lamination

The eddy current loss is proportional to;

  • Square of the eddy current(I2)
  • Resistance of the core (R)
Eddy Current loss (We) = K x I2 R     (Where K is the eddy current constant)

From above it is clear that the higher the current, the higher is the loss. The solid core has a larger cross-section area, therefore it has lower resistance. According to Ohm’s Law, the lower resistance causes a higher current in the circuit.

I = V/R

As a result, the magnitude of the current(I) will be very high. The higher current leads to higher eddy current loss(I2R loss).

How to Reduce Eddy Current Loss?

We can reduce the eddy current loss by reducing the current. The current reduces with increased core resistance. We can decrease the core resistance by;

  • With the use of thin laminated sheets in the core
  • With the use of high resistivity silicon steel for core material 

The core is made from thin laminated sheets. The lamination on sheets provides electrical insulation between two adjacent sheets. The thin sheet has a smaller cross-section area ( R = ρL/A) and therefore its resistance is more. The large resistance hinders the path of eddy currents. Thus, the magnitude of current and loss reduces.

The other method of reducing current and loss is the use of a CRGO(Cold Rolled Grain Oriented ) Steel core. The CRGO steel core has higher electrical resistance and thus the loss reduces.  

Mathematical Expression for Eddy Current Loss

We can calculate the loss with the mathematical equation given below.