What is the Difference Between Eddy Current Loss and Hysteresis Loss

Energy can’t be created or destroyed, but it can’t be perfectly used either. When we use energy for a certain purpose, some amount of energy is lost. Eddy current loss and hysteresis loss are both energy losses that occur in AC (alternating current) applications, especially in magnetic components like transformers and motors.

What is the difference between eddy current loss and hysteresis loss? Eddy current loss is related to the conductivity of the material and the induced currents that flow within it due to the changing magnetic field, whereas hysteresis loss is related to the magnetic properties of the material and the energy required to repeatedly magnetize and demagnetize it.

Key Areas Covered

1. What is Eddy Current Loss 
      – Definition, Features, Applications
2. What is Hysteresis Loss
      – Definition, Features, Applications 
3. Similarities Between Eddy Current Loss and Hysteresis Loss
      – Outline of Common Features
4. Difference Between Eddy Current Loss and Hysteresis Loss
      – Comparison of Key Differences
5. FAQ: Eddy Current Loss and Hysteresis Loss
      – Answers to Frequently Asked Questions

Key Terms

Eddy Current Loss, Hysteresis Loss

What is Eddy Current Loss

Eddy current loss is also known as iron loss. Eddy currents are swirling loops of electric current induced within conductors by a changing magnetic field. Conductors have some resistance, and when the eddy currents encounter this resistance, they dissipate energy as heat. This heat generation is entirely unwanted – it reduces the efficiency of the device and can even cause overheating. The strength of the eddy current loss depends on several factors, such as conductivity and frequency of the AC field. More losses are seen in highly conductive materials like copper or thick steel.

Figure 1: Eddy Current

Higher frequencies of AC field mean faster changes in the magnetic field, which in turn induce stronger eddy currents and greater heat loss. Lamination is a strategy that helps to eliminate the eddy current loss. Instead of a solid core, the magnetic component is built from thin sheets of steel, typically silicon steel, which also has lower hysteresis loss. These laminations are insulated from each other, essentially creating tiny air gaps that disrupt the flow of eddy currents. Furthermore, applications of eddy current loss include induction cooking, metal detection, and induction heating.

What is Hysteresis Loss

Hysteresis loss is the energy wasted as heat when a magnetic material is repeatedly magnetized and demagnetized. It occurs whenever a magnetic material is subjected to a constantly changing magnetic field (for example, in transformers and motors). There are a few factors that affect the amount of energy loss in hysteresis. Two of them are material properties and frequency of the AC field.

Figure 2: Magnetic Hysteresis

Different materials have varying hysteresis loops. A material with a wider loop signifies greater energy loss during domain reorientation. For example, some types of steel have a higher hysteresis loss compared to silicon steel. When considering the frequency of the AC field, the faster the magnetic field changes direction (higher frequency), the more frequently the domains need to reorient, leading to greater hysteresis loss. Hysteresis loss reduces the overall efficiency of AC devices.

Similarities Between Eddy Current Loss and Hysteresis Loss

1. They both represent wasted energy that ultimately dissipates as heat.
2. Both losses are a consequence of the constantly changing magnetic field in AC applications.
3. They contribute to the inefficiency of AC devices by converting some of the usable electrical energy into unwanted heat.

Difference Between Eddy Current Loss and Hysteresis Loss

Definition

• Eddy current loss refers to energy loss caused by circulating currents induced in conductive materials by alternating magnetic fields. Hysteresis loss is the energy lost as heat when magnetic materials undergo repeated magnetization and demagnetization cycles due to alternating magnetic fields.

Cause

• Eddy current loss is caused by induced currents within a conductor due to a changing magnetic field while hysteresis loss is caused by the reorientation of magnetic domains within a magnetic material when subjected to a changing magnetic field.

Material Dependence

• Eddy current loss is highly dependent on the conductivity of the material, while hysteresis loss depends on the inherent magnetic properties of the material.

Location of Loss

• Eddy current loss occurs within the conductor itself, where the eddy currents flow and dissipate energy as heat. On the other hand, hysteresis loss occurs within the magnetic material itself due to the energy used in flipping magnetic domains.

Beneficial Applications

• Although eddy current loss is a loss, the phenomenon itself has applications like induction heating and eddy current testing. Meanwhile, hysteresis loss has no direct beneficial applications, but the properties of hysteresis loops are valuable for material characterization and sensor development.

Conclusion

Eddy current loss and hysteresis loss are both energy losses that occur in AC (alternating current) applications. Eddy current loss is caused by induced currents within a conductor due to a changing magnetic field, while hysteresis loss is caused by the reorientation of magnetic domains within a magnetic material when subjected to a changing magnetic field.

FAQ: Eddy Current Loss and Hysteresis Loss

1. What is meant by eddy current?

Eddy currents are electric currents looping within conductors when a changing magnetic field cuts through them. They can cause heat loss and oppose the magnetic field that created them.

2. What do you mean by hysteresis?

Imagine a magnet; its magnetism lags behind the changing magnetic field it’s exposed to, creating a loop-shaped effect. This “lag” is what hysteresis describes.

3. What are eddy current examples?

Everyday examples of eddy currents include braking in trains (magnetic field slows wheels), metal detectors (eddy currents signal the presence of metal), and induction cooktops (eddy currents heat cookware).

4. How to reduce eddy current loss?

To reduce eddy current loss there are two main strategies. The first method uses laminated conductors, whereas the second uses low conductivity materials.

5. How to reduce hysteresis loss?

You may select soft magnetic materials and reduce operating field strength. This is because lowering the magnetic field a material experiences shrinks the loop and cuts hysteresis loss.

Reference:

1. “Hysteresis Loss – An Overview.” Science Direct. 
2. “Eddy Current Loss – An Overview.” Science Direct. 

Image Courtesy:

1. “Eddy Current” By Evan Mason – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Magnetic hysteresis” By Tem5psu (CC BY-SA 4.0) via Commons Wikimedia