Definition and Principle
Different from copper loss, the iron loss of a transformer is not related to factors such as the winding and the magnitude of the current. As the name implies, the iron loss is related to the iron core. It is generated by the iron core. The iron loss of a transformer is also known as the "no-load loss" because it exists both under the full-load and zero-load states of the transformer and is a fixed loss of the transformer. However, in the load, the power loss will decrease as the electric field strength decreases.
Classification
The iron loss of a transformer is divided into hysteresis loss and eddy current loss.
● Hysteresis Loss
The working principle of a transformer is based on the principle of electromagnetic induction to achieve the step-up, step-down of voltage and the change of current. The magnetic flux in the transformer flows on the iron core. The iron core has magnetic resistance to the magnetic flux, just as a conductor has resistance to the current, and heat will be generated. Such a loss is called the "hysteresis loss".
● Eddy Current Loss
When the primary winding of the transformer is energized, the magnetic flux generated by the coil flows in the iron core. Since the iron core itself is also a conductor, an induced electromotive force will be generated on the plane perpendicular to the magnetic field lines. This electromotive force forms a closed loop on the cross-section of the iron core and generates a current, which is like a vortex, so it is called an "eddy current". The loss generated by this eddy current is called the "eddy current loss". It is precisely because the eddy current is generated in the iron core that the iron core is made into thin pieces, because the thinner it is, the greater the resistance and the smaller the current.
Influencing Factors
Operating voltage and frequency: The iron loss is related to the operating voltage and frequency of the transformer because these factors will affect the magnetic field strength and hysteresis phenomenon in the iron core.
Core material: The hysteresis properties of the core material will affect the magnitude of the iron loss. If the core material is not well selected, the hysteresis loss will increase.
Manufacturing process: The manufacturing process of the transformer also has a certain impact on the iron loss. For example, the lamination method of the iron core, insulation treatment, etc. will all affect the magnitude of the iron loss.
Calculation Method
Formula based on rated current and hysteresis and resistance losses:
Iron loss (unit: kVA) = I² × (Rm + Ra)
Where I is the rated current of the transformer, Rm is the hysteresis loss of the iron core, and Ra is the resistance loss of the iron core.
Formula based on constants, magnetic flux density and operating frequency:
P_iron = Kf × (Bm)^2 × f
Where P_iron is the iron loss, Kf is a constant, Bm is the magnetic flux density, and f is the operating frequency of the transformer.
Reduction Methods
Select high-quality core materials: Selecting core materials with low hysteresis loss can reduce the iron loss of the transformer.
Optimize the manufacturing process: By improving the manufacturing processes such as the lamination method of the iron core and insulation treatment, the iron loss can be reduced.
Reasonable design: In the design stage of the transformer, the iron loss can be reduced by optimizing the structural design and parameter selection.
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