Question

How do hysteresis losses occur in a transformer core?

Answer 1

Hysteresis losses in a transformer core occur due to the continuous reversal of the magnetic field within the core material. Here's how this happens:

1. Magnetic Field Reversal: A transformer works by using an alternating current (AC) to create a magnetic field in the core. This magnetic field constantly changes direction (because AC reverses its polarity periodically).
   

1. Magnetic Domains: The core of a transformer is usually made of ferromagnetic material (like iron). These materials contain tiny regions called magnetic domains, where the magnetic moments of atoms are aligned in the same direction. When an external magnetic field is applied (like the one created by the AC in the transformer), these domains tend to align with the applied field.
   

1. Energy Loss in Reversing: Every time the magnetic field direction changes, the magnetic domains in the core also try to realign themselves with the new direction. However, this realignment is not perfect, and some energy is lost as heat during this process. This loss of energy is what we call hysteresis loss.
   

1. Loop in the B-H Curve: The relationship between magnetic field strength (H) and magnetic flux density (B) for a material is shown in a curve called the B-H curve. When the magnetic field is reversed, the material’s magnetization doesn’t immediately follow the applied field; instead, it forms a loop, showing that energy is lost each time the field changes direction. The area inside this loop represents the energy lost due to hysteresis.
   

1. Factors Affecting Hysteresis Loss:
   

   - Material Properties: The type of material used in the core affects how easily the domains can realign. High-quality transformer steel (like silicon steel) is used to minimize hysteresis losses.
   - Frequency: Since the magnetic field in a transformer alternates at the frequency of the AC supply, higher frequencies will result in more frequent realignment of the domains, leading to higher hysteresis losses.
   - Magnetic Field Strength: Stronger magnetic fields will require more energy to realign the domains, increasing hysteresis losses.

In summary, hysteresis losses in a transformer occur because of the energy required to reorient the magnetic domains in the core material as the magnetic field changes direction with the alternating current. This energy is dissipated as heat and represents a loss in efficiency.