In a practical transformer, iron (core) losses remain nearly constant from no-load to full-load operation. This means that the power loss occurring in the transformer core does not change significantly with changes in the load current.

Iron losses consist of two main components:

1. Hysteresis loss
2. Eddy current loss

Both of these losses are produced by the alternating magnetic flux in the transformer core and depend mainly on the supply voltage, frequency, and core material properties, rather than on the load current.

1. Hysteresis Loss

Hysteresis loss is caused by the continuous reversal of magnetization in the iron core as the alternating current produces an alternating magnetic field.

During every AC cycle, the core undergoes repeated magnetization and demagnetization. This repeated reversal requires energy because of the inherent magnetic properties of the core material, and the energy is dissipated as heat.

The magnitude of hysteresis loss depends on:

• The area of the hysteresis loop of the core material.
• The frequency of the alternating supply.
• The magnetic properties of the core, such as coercivity and magnetic permeability.

Since these factors remain practically constant for a transformer operating at constant supply voltage and frequency, hysteresis loss is essentially independent of the load current.

2. Eddy Current Loss

Eddy current loss is caused by circulating currents induced within the transformer core due to the alternating magnetic flux.

These induced currents flow through the resistance of the core material, producing heat and resulting in power loss.

The magnitude of eddy current loss depends on:

• The electrical resistivity of the core material.
• The frequency of the alternating supply.
• The core geometry and thickness of the laminations.

Since these factors are determined by the transformer design and operating frequency, eddy current loss also remains practically independent of the load current.