What is Eddy current loss?
According to Faraday’s law of electromagnetic induction, an emf is induced in a material when an alternating magnetic field is applied to a material with the magnetic property.
The EMF’s current flow rotates all around the magnetic material’s body due to the magnetic property of the conducting material. This rotating current is known as Eddy Current. They will happen when the conductor is subjected to a changing magnetic field.
Because these currents aren’t doing any useful work, they cause an Eddy Current Loss (I2R loss) in the magnetic material.
The loss of eddy currents is caused by the relative motion of the core and the magnetic flux.
Eddy current loss formula
The equation to find eddy current loss is given as:
Pe(W) = Ke x Bm2 x F(hz)2 x t2 x V Watts
V = h x L x t meter
Pe = eddy current loss (W)
Ke = eddy current constant
B = Density of the flux (Wb/m2)
f = Magnetic reversal’s frequency per second (Hz)
t = Thickness of the material (m)
V = Volume (m3)
Eddy current losses for Per unit volume
Pe (W) = Ke x B m 2 x F (hz) 2 x t 2 Watts
How to reduce Eddy current loss?
We can reduce the eddy current loss by doing the following methods.
- Increase the core’s resistance
- Each and every steel sheet in the transformer is insulated by using a thin layer of varnish
- The resistance will be high with the laminations are thin
- The planes of these sheets are perpendicular to the direction of the current created by the induced emf. To cut the flow of eddy current paths, sheet planes are arranged parallel to the magnetic field.
- The eddy currents are restricted to the thin sheets due to the high resistances between the sheets. An eddy current will circulate within each lamination sheet. Tiny eddy currents continue to exist, but only within each thin sheet, and their magnitude is greatly reduced.
- When compared to using a single solid iron core, the sum of individual eddy currents of all laminations is very small.
Uses of Eddy current
- In speedometer of the vehicle.
- In magnetic breaks and energy meters
- In induction furnaces
- In electromagnetic NDT methods to find any fractures, and other discontinuities in material or its surface
What is Hysteresis loss?
The magnetization and demagnetization of the core as current flows forward and backward causes hysteresis loss. The magnetic flux increases as the magnetizing force (current) increases. When the magnetizing force (current) is reduced, the magnetic flux decreases more gradually rather than at the same rate. As a result, even when the magnetizing force is zero, the flux density remains positive. To achieve zero flux density, the magnetizing force must be applied in the negative direction.
Hysteresis loss formula
The equation for hysteresis loss is given as:
Pb = η * Bmaxn * f * V
Pb = hysteresis loss (W)
η = Steinmetz hysteresis coefficient, depending on the material (J/m3)
Bmax = maximum flux density (Wb/m2)
n = Steinmetz exponent, ranges from 1.5 to 2.5, depending on material
f = frequency of magnetic reversals per second (Hz)
V = volume of magnetic material (m3)
How to reduce Hysteresis loss? Hysteresis loss can be controlled by following methods
- Use material with less area hysteresis loop.
Ex: Silica steel has very less area for hysteresis loss
- Use the material which reaches zero/non-zero flux when the current flow is stopped
- Increase the number of laminations between the plates.
Use of Hysteresis loss
- It provides data on coercivity, susceptibility, retentivity, energy loss throughout a single cycle of magnetization for every ferromagnetic material
- Hysteresis loops are playing a major role in the designing of various electrical devices
Difference between Eddy Current loss and Hysteresis loss
| S.No | Eddy current loss | Hysteresis loss |
|---|---|---|
| 1 | Eddy current loss is due to the relative motion between the core and magnetic flux | It is due to the reversal of magnetism (movement of tiny molecular magnets) |
| 2 | Loss occurs in the conductor, core, and body of the machine | Loss occurs only in the core of the machine |
| 3 | Occurs in conducting material | Occurs in magnetic material |
| 4 | Can be reduced by the lamination in the core | To reduce hysteresis loss, use grain-oriented steel |
| 5 | It occurs due to the interaction of the conductor and magnetic flux | It is due to the flux’s` reversal |
| 6 | Pe(W) = Ke x Bm2 x F(hz)2 x t2 x V Watts | Pb = η * Bmaxn * f * V |