1 Answer
Hysteresis and eddy current losses are both types of core losses that occur in the magnetic materials of transformers, electric motors, and other electrical machines. Though both result in energy dissipation in the form of heat, they arise from different physical phenomena. Here’s how you can separate the two:
1. Hysteresis Loss:
- Cause: Hysteresis loss occurs due to the lag between the magnetization and demagnetization of the material when the magnetic field is alternated (AC supply). As the magnetic field in the core material changes direction, some energy is lost due to the material's resistance to changing its magnetization. This effect is related to the material's magnetic properties and the area enclosed in the B-H curve (magnetic flux density vs. magnetic field strength).
- Dependence:
- Hysteresis loss depends primarily on the frequency of the alternating magnetic field and the magnetic properties of the material (such as the coercivity and remanence).
- The amount of loss increases with higher frequencies and is proportional to the hysteresis loop area in the material’s B-H curve.
- Formula: \( W_h = \eta B_{\text{max}}^2 f V \)
- Where:
- \( W_h \) is the hysteresis loss,
- \( \eta \) is a constant depending on the material,
- \( B_{\text{max}} \) is the maximum magnetic flux density,
- \( f \) is the frequency,
- \( V \) is the volume of the core.
2. Eddy Current Loss:
- Cause: Eddy current loss arises due to circulating currents (eddy currents) induced within the conductive material when the magnetic field changes. These currents create resistive losses in the material as they flow through it.
- Dependence:
- Eddy current losses depend on the rate of change of the magnetic field (i.e., frequency), the thickness of the material, and the resistivity of the core material. Higher frequencies and thicker materials tend to increase eddy current losses.
- Formula: \( W_e = k \cdot B_{\text{max}}^2 f^2 t^2 \)
- Where:
- \( W_e \) is the eddy current loss,
- \( k \) is a constant related to the material's resistivity,
- \( t \) is the thickness of the core material,
- \( f \) is the frequency,
- \( B_{\text{max}} \) is the maximum magnetic flux density.
How to Separate the Losses:
2. Reduce the frequency (or use DC magnetization for a steady magnetic field) and observe the loss due to hysteresis (since eddy current loss is frequency-dependent).
3. Compare the change in loss as you vary the thickness of the core. A larger increase in loss as the thickness increases points to eddy current losses.
In Short:
By varying these parameters, you can effectively separate and study the two types of losses in a magnetic material.
1. Hysteresis Loss:
- Cause: Hysteresis loss occurs due to the lag between the magnetization and demagnetization of the material when the magnetic field is alternated (AC supply). As the magnetic field in the core material changes direction, some energy is lost due to the material's resistance to changing its magnetization. This effect is related to the material's magnetic properties and the area enclosed in the B-H curve (magnetic flux density vs. magnetic field strength).- Dependence:
- Hysteresis loss depends primarily on the frequency of the alternating magnetic field and the magnetic properties of the material (such as the coercivity and remanence).
- The amount of loss increases with higher frequencies and is proportional to the hysteresis loop area in the material’s B-H curve.
- Formula: \( W_h = \eta B_{\text{max}}^2 f V \)
- Where:
- \( W_h \) is the hysteresis loss,
- \( \eta \) is a constant depending on the material,
- \( B_{\text{max}} \) is the maximum magnetic flux density,
- \( f \) is the frequency,
- \( V \) is the volume of the core.
2. Eddy Current Loss:
- Cause: Eddy current loss arises due to circulating currents (eddy currents) induced within the conductive material when the magnetic field changes. These currents create resistive losses in the material as they flow through it.- Dependence:
- Eddy current losses depend on the rate of change of the magnetic field (i.e., frequency), the thickness of the material, and the resistivity of the core material. Higher frequencies and thicker materials tend to increase eddy current losses.
- Formula: \( W_e = k \cdot B_{\text{max}}^2 f^2 t^2 \)
- Where:
- \( W_e \) is the eddy current loss,
- \( k \) is a constant related to the material's resistivity,
- \( t \) is the thickness of the core material,
- \( f \) is the frequency,
- \( B_{\text{max}} \) is the maximum magnetic flux density.
How to Separate the Losses:
- Material Properties: Hysteresis loss is a material-dependent property, typically higher in ferromagnetic materials with high coercivity. Eddy current loss depends on both the material's electrical conductivity and the thickness of the core material.
- Frequency Dependence: Both losses depend on frequency, but eddy current losses increase with the square of frequency, while hysteresis losses increase linearly with frequency. By varying the frequency and measuring the losses, you can distinguish the two.
- Thickness of the Core Material: Eddy current losses increase with the square of the thickness of the core. So, reducing the thickness of the core reduces eddy current losses (hence why transformer cores are often made of thin laminations). Hysteresis loss, on the other hand, is relatively less affected by thickness.
- Separation through Experimentation: One experimental method to separate them is to:
2. Reduce the frequency (or use DC magnetization for a steady magnetic field) and observe the loss due to hysteresis (since eddy current loss is frequency-dependent).
3. Compare the change in loss as you vary the thickness of the core. A larger increase in loss as the thickness increases points to eddy current losses.
In Short:
- Hysteresis Loss: Related to the material’s magnetic properties, and is more prominent at low frequencies. It’s mostly independent of the material thickness.
- Eddy Current Loss: Related to the induced currents within the material, and depends heavily on frequency and the thickness of the core.
By varying these parameters, you can effectively separate and study the two types of losses in a magnetic material.