Hysteresis & Core Loss in Induction Motors: SMC Vs. Steel Lamination.

Posted by Horizon Technology - December 02, 2019

Have you ever wished you had superpowers that could stop both hysteresis and eddy current loss in a project that demanded high magnetic performance?

Core loss in magnetic material is a measure of the heat generated within the material as a result of the alternating current. High core losses equal a greatly inefficient magnetic part.

An inefficient magnetic part can bring down your whole design. A little lesson about materials can show you how to minimize hysteresis loss and core loss in induction motors and other AC applications ...

Hysteresis & Core Loss in Induction Motors & Other AC Machines

Total core loss is actually the combination of two types of loss. Here's the difference between hysteresis loss and eddy current loss:

  • Eddy current loss: When changing frequencies, energy is consumed. Magnetic induction lags behind the magnetizing force
  • Hysteresis loss: When changing frequencies, energy is consumed

Both increase the heat level in the magnetic material. Heat = inefficiency. (We’ll give a much longer equation for you to use in a bit.)

Eddy current loss occurs in all AC devices, including:

  • Motors
  • Transformers
  • Power supplies
Eddy current loss in motors is a common complaint of design engineers, but one you can address more easily than you think ...

Total Core Loss Chart

Let’s get more specific. Core losses in soft magnetic composite materials depend on the:

  • Material used
  • Component density
  • Heat treating

The following chart shows the total core loss of an increasingly popular soft magnetic composite (SMC) material. The chart also compares it to traditional M47 and M19 steel lamination (electrical steel) materials, both semi-processed to a 24 gauge (0.025” thick).

Hysteresis Line Graph(Measured at an induction level of 1.5 Tesla.)

The SMC's losses are lower than the M47 electrical steel at frequencies above 100 Hz or so. Meanwhile, SMC losses vs. the M19 electrical steel are lower at frequencies above 400 Hz, give or take a few.

The chart clearly shows that soft magnetic composite is best at higher frequencies. It’s also apparent that SMCs are superior to M47 laminate at frequencies above 400 Hz. 

This core loss data assumes the SMCs were compacted to a density of 7.5 g/cm³. The data for the laminations was based on the core loss at 60 Hz for each of the two materials, then extrapolated using this core loss formula:

Core losses SMC materials formula A

And here's the hysteresis loss and eddy current losses formula for the SMC material: 

Hysteresis & Core Loss in Induction Motors - smc formulaHysteresis & Core Loss in Induction Motors - formula explanation

In the hands of your smartest engineer (maybe that’s you), this equation can calculate your core losses at any level of:

  • Induction
  • Frequency
  • Part thickness

In other words, you can learn how much heat (aka total core loss) you’ll generate using a soft magnetic composite at densities below 7.5 g/cm³ under any specific condition. Remember that higher resistivity generates less heat.

The above "SMC 700 5P" represents the optimal soft magnetic composite. There are also variations of this state-of-the-art material available to cater to your performance and budgetary needs. This table gives the values for each of the three major grades of soft magnetic composite:

core loss in induction motor hysteresis loss in induction motor - chart of constants

How to Minimize Hysteresis Loss

So, how to reduce eddy current and hysteresis losses? The proof is in the numbers: Soft magnetic composites go where limited laminations cannot. As a designer or purchaser, it’s crucial you know the uses of soft magnetic composite compared with steel lamination:

  • Unique shape-making ability
  • Reduce number of parts per assembly
  • And the reduced losses we’ve talked about!

Soft magnetic composite materials are starting to outperform standard lamination materials at frequencies as low as 400. SMC even beat the popular, high-performing M19 lamination at lesser heat

SMC is attractive for new, modern, high frequency applications.

However, they are not historically ideal for induction motors used in fridges, air conditioners, etc.

That said, if you can reduce the operating cost of the product, you can spend more money on optimizing your motor. You’ll eventually save the extra money you put in on the front end.

Some pretty smart people are starting to use this concept. We hope you capitalize on the potential of soft magnetic composite, too.

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(Editor's note: This article was originally published in September 2018 and was recently updated.)

Topics: Powdered Metallurgy, Magnetics, Materials, Applications, motors

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