What is Core Loss?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 18 November 2019
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Also known as iron loss or excitation loss, core loss is a situation in which there is some change in the magnetization of the materials that make up the core in a transformer or some type of induction equipment. This change has an adverse effect on the rate of energy conversion that normally takes place, creating a loss of energy and efficiency. Fortunately, core losses can be isolated and repaired, making it possible to restore the core to full efficiency.

A core loss takes place when the stability of the magnetic field within the core changes in some manner. The result is some type of current loss that can eventually damage the core unless the magnetic field is stabilized. There are actually two common types of core losses that can take place, depending on the underlying reasons for the instability of the magnetic field.

One example of a core loss is known as a hysteresis loss. In this scenario, the components in the core material contract and expand in a way that causes the flow of energy to dissipate. When this type of dissipation takes place, the energy is converted to heat. The loss of energy will escalate as the equipment continues to run through additional cycles and the magnetic field becomes increasingly unbalanced.


A second form of core loss is known as an eddy current loss. Here, the core material resists the flow of currents, creating a conversion of energy into heat. This effectively reduces the flow of energy through an inductor. Laminating the core material can help to reduce the potential for this particular type of core loss. Another solution is to make use of core components that are constructed with materials that are less conductive and less likely to be resistant to the flow of the eddy current.

Fortunately, there are ways to determine the origin of a core loss and take action to correct the situation. Testing equipment can be used to spot check the performance of the core from time to time, as well as identify the underlying cause of the disruption in the magnetic field. Identifying the presence of a transformer core loss early on not only minimizes the loss of energy but also aids in minimizing wear and tear on the core itself. This in turn means that there is less money spent in compensating for the lost energy, and minimizes the need to frequently replace transformers or induction equipment that has been severely damaged.


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Post 3

Something to keep in mind: The contraction and expansion is not the core's. It is expansion and contraction of the tiny magnetic domains it is composed of.

Post 2

@SkyWhisperer - That’s an interesting theory. I don’t think it would have anything to do with core loss however, because these units are designed to withstand much more than heat and cold.

I work in the utility industry, and can tell you that transformers, circuit breakers, relays and the like are designed to withstand large spikes of electrical current.

Only a core loss tester used by a technician out in the field would reveal the real cause of the problem.

Post 1

Since a core loss can happen because of a process of expansion and contraction, I wonder if a core loss test would take weather into consideration as being a possible culprit?

Since cold causes things to contract and heat causes things to expand, I would think that this might be a possibility.

Admittedly, they would have to be very extreme weather conditions in my opinion, as I am sure that these components are insulated well enough to protect them from the ups and downs of typical weather cycles.

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