Electrical steel core loss generally increases as frequency rises, but the relationship is not linear. A loss value measured at 50 Hz cannot simply be scaled to predict performance at 100 Hz or several hundred hertz.

This matters when comparing electrical steel grades for transformers, motors, and other magnetic applications. Frequency is only one part of the test condition. The reported loss also depends on how and under what conditions the material was tested.

Key Learning Points

Core loss increases with frequency because different loss components respond differently as frequency rises.
Core-loss values measured at different frequencies should not be compared directly.
Core-loss values are meaningful only when their test conditions are known.
Lower 50 Hz core loss does not necessarily mean better performance at higher frequencies.

Why Core Loss Increases with Frequency

Core loss, also called iron loss, is the energy dissipated as heat when electrical steel is repeatedly magnetized and demagnetized. As frequency increases, the magnetic field changes direction more often within the same period of time, causing total core loss to rise.

However, the relationship is not simply proportional. Doubling the frequency does not necessarily mean that total core loss will double.

This is because different loss components respond differently to frequency. Hysteresis loss and classical eddy-current loss are two of the main components used to explain this behavior.

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Electrical steel core loss frequency curve comparing hysteresis loss and eddy current loss

Hysteresis Loss vs. Eddy Current Loss

Hysteresis Loss (Ph): Changing Magnetized Areas Requires Energy

Hysteresis loss is associated with the repeated movement and reversal of magnetic domains as the magnetic field changes direction. Energy is dissipated during each magnetization cycle.

Under simplified conditions, hysteresis loss increases approximately with frequency:

Ph ∝ f

More magnetic cycles per second generally mean more hysteresis-related energy loss.

Classical Eddy-Current Loss (Pe)

A changing magnetic field also induces circulating electrical currents within the steel sheet. These eddy currents dissipate energy as heat as they flow through the material.

Under a simplified classical model, eddy-current loss has a stronger frequency dependence:

Pe ∝ f²

This helps explain why eddy-current loss becomes increasingly important as frequency rises.

The Combined Effect and Total Core Loss

In practical loss-separation models, total core loss can be represented as a combination of hysteresis, classical eddy-current, and excess loss:

Ptotal ≈ Ph + Pe + Pex

Actual measured loss curves depend on the material and test conditions, so the simplified relationships above should be used to explain trends rather than to predict exact values.

How to Compare Core Loss Data at Different Frequencies

Manufacturer datasheets report core loss under specific test conditions. The W/kg value should therefore be read together with frequency, flux density, thickness, and the applicable test method. For example, P1.5/50 refers to a loss value measured at the specified 1.5 T magnetic condition and 50 Hz frequency.

Can 50 Hz Core Loss Be Compared with 60 Hz Data?

Core loss at 60 Hz will generally be higher than at 50 Hz when the other test conditions remain comparable. However, there is no single conversion factor that applies to every electrical steel grade.

The exact difference depends on the grade and the relative contribution of different loss components. For approximate comparison, 50 Hz data may provide a reference, but measured 60 Hz data is preferable when accurate material evaluation is required.

Does Lower 50 Hz Core Loss Mean Better High-Frequency Performance?

Not necessarily. Two electrical steel grades that perform similarly at 50 Hz may behave differently as frequency increases.

Sheet thickness is one reason the difference between grades can become more noticeable as frequency rises. For applications such as high-speed motor cores, loss data measured closer to the actual operating frequency is therefore more useful than a 50 Hz value alone.

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Electrical steel core loss test conditions including frequency flux density thickness test method and waveform

Test Conditions That Affect the Comparison

When comparing core-loss data from different suppliers, check whether the following test conditions are comparable:

Flux Density: Core loss can change significantly with magnetic flux density, so values measured at different B levels should not be compared directly.
Test Method: The Epstein test method is standardized for measuring magnetic properties including core loss under specified excitation conditions. Epstein frame and Single Sheet Tester results should not be treated as directly interchangeable.
Sample Condition: Cutting, punching, and stress-relief annealing can affect measured magnetic performance.
Waveform: Inverter-fed operation may introduce harmonics that are not represented by the nominal fundamental frequency alone.

Why Sheet Thickness Matters at Higher Frequency

Sheet thickness affects the eddy-current component of core loss. As frequency rises, thinner electrical steel laminations can help limit circulating currents within the steel.

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Thin electrical steel laminations reduce eddy current loss in high frequency motor applications

However, thickness should not be evaluated alone. High-frequency performance should still be compared using measured core-loss data at similar flux density, frequency, and test conditions.

Conclusion

A core-loss value should not be separated from the conditions under which it was measured. When comparing electrical steel grades, the useful comparison is between data taken at comparable frequency, flux density, thickness, and test conditions.

For applications above conventional 50/60 Hz operation, measured loss data closer to the intended operating frequency provides a more relevant basis for material comparison.

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