---
title: "Eddy Current Loss | Circuits and Systems II"
description: "Eddy current loss is heat wasted in a conductor by induced circulating currents from changing magnetic fields, lowering transformer efficiency in Circuits II."
canonical: "https://fiveable.me/electrical-circuits-systems-ii/key-terms/eddy-current-loss"
type: "key-term"
subject: "Electrical Circuits and Systems II"
unit: "Unit 7"
---

# Eddy Current Loss | Circuits and Systems II

## Definition

Eddy current loss is the heat energy lost in a conducting core when a changing magnetic field induces circulating currents. In Electrical Circuits and Systems II, it shows up in non-ideal transformer models.

## What It Is

Eddy current loss is the power a transformer wastes as heat because a changing magnetic field induces closed-loop currents inside its conductive core. In Electrical Circuits and Systems II, this is one of the main non-ideal effects that keeps a real transformer from behaving like the perfect one you see in the ideal equations.

The basic idea is simple: when magnetic flux in the core changes with time, Faraday’s law says a voltage is induced in any conducting path inside that material. If the core is solid metal, those paths form loops, and the induced currents circulate through the core itself. Those currents are called eddy currents, and the resistance of the core turns their electrical energy into heat.

That heat is not doing useful work at the load. Instead, it becomes a core loss that reduces efficiency and can raise the temperature of the transformer. Higher temperature can also affect insulation, winding resistance, and long-term reliability, which is why eddy current loss is not just a theory detail, it changes how engineers design actual equipment.

The size of the loss depends on how fast the magnetic field changes and on the geometry and material of the core. Higher frequency usually means more loss, which is why eddy current effects become more noticeable in higher-frequency AC systems. Thicker conductive material also gives currents more room to form larger loops, so losses increase as core thickness increases.

Engineers fight this by breaking the core into thin laminated sheets instead of using one solid block. The insulation between laminations interrupts the loop paths, so the induced currents stay small. Lower-conductivity core materials can also reduce the current size, which is why material choice matters so much in transformer design.

A common mistake is to think eddy current loss is the same thing as copper loss. Copper loss happens in the windings because of the winding resistance, while eddy current loss happens in the core because of induced circulating currents. In a non-ideal transformer model, those are different loss terms, and you need both if you want the model to match real behavior.

## Why It Matters

Eddy current loss is one of the reasons transformer analysis in Electrical Circuits and Systems II moves beyond ideal voltage ratios and into real power flow. When you study non-ideal transformer characteristics and equivalent circuits, you are not just tracking how voltage changes from primary to secondary. You are also tracking where input power disappears as heat.

That matters anytime you need to predict efficiency, temperature rise, or how a transformer behaves under different frequencies. For example, a design that works fine at power-line frequency may waste much more power if the frequency increases, because eddy current loss grows quickly with changing magnetic field rate. That is why frequency response and power system behavior come up together in this course.

It also helps you interpret equivalent circuits correctly. Core-loss resistance and related loss elements are how engineers represent the energy that does not reach the load. If you can tell eddy current loss apart from winding resistance and hysteresis loss, you can explain why a transformer’s performance changes when the load, frequency, or core material changes.

## Connections

### Hysteresis Loss

Both are core losses in a transformer, but they come from different physics. Hysteresis loss is tied to repeatedly magnetizing and demagnetizing the core material, while eddy current loss comes from circulating currents induced inside the core. When you separate transformer losses, you usually treat them as different contributors to total core loss.

### Transformer Efficiency

Eddy current loss lowers transformer efficiency because part of the input power turns into heat instead of reaching the load. When you calculate efficiency, you need to account for core losses along with copper loss. A transformer with more eddy current loss will run less efficiently, especially at higher frequencies or with a poorly designed core.

### [Eddy Currents](/electrical-circuits-systems-ii/key-terms/eddy-currents)

Eddy currents are the circulating currents themselves, while eddy current loss is the energy those currents dissipate. The term with "currents" names the physical motion of charge, and the term with "loss" names the heat and wasted power that results. In transformer problems, you usually identify the currents first and then connect them to the loss.

### Magnetic Flux Density

Changes in magnetic flux density drive the induced voltages that create eddy currents. If the flux density in the core changes faster or more strongly, the induced currents can become larger, which increases loss. That is why flux behavior matters when you analyze transformer operation at different input frequencies or core conditions.

## On the AP Exam

A problem set or quiz question will usually ask you to identify where the loss comes from, compare it with hysteresis loss or copper loss, or explain why a laminated core reduces heating. In a calculation problem, you may be given transformer operating conditions and asked which change would increase or reduce core loss, especially when frequency or core thickness changes.

You might also see a non-ideal transformer diagram and need to label the loss element that represents core heating. If the question mentions efficiency, temperature rise, or high-frequency operation, think about whether eddy current loss is the main issue. The safest move is to connect the changing magnetic field to induced currents in the core, then to heat and reduced efficiency.

## Eddy Current Loss vs Hysteresis Loss

Eddy current loss and hysteresis loss are both transformer core losses, so they are easy to mix up. Eddy current loss comes from induced circulating currents in the core material, while hysteresis loss comes from repeatedly reversing the magnetic domains in the core. If the question mentions current loops, laminations, or conductive heating, think eddy currents. If it mentions magnetization reversal, think hysteresis.

## Key Takeaways

- Eddy current loss is the heat wasted in a transformer core when changing magnetic flux induces circulating currents inside the conductor.
- In Electrical Circuits and Systems II, it is one of the main non-ideal effects that makes real transformers less efficient than ideal ones.
- The loss grows when frequency increases and when the conductive core is thicker, because both changes make larger current loops easier to form.
- Laminated cores reduce eddy current loss by breaking up the path for circulating currents and limiting their size.
- Do not mix it up with copper loss or hysteresis loss, since each one comes from a different part of the transformer.

## FAQs

### What is eddy current loss in Electrical Circuits and Systems II?

It is the power lost as heat in a transformer core when a changing magnetic field induces circulating currents in the conductor. In this course, it shows up as a non-ideal core loss that lowers efficiency. You usually discuss it when comparing ideal and real transformer behavior.

### Why do laminated cores reduce eddy current loss?

Laminations split the core into thin insulated layers, which disrupts the large loop paths that eddy currents need. Smaller loops mean smaller induced currents and less heat. That is why laminated steel is a standard transformer design choice.

### Is eddy current loss the same as copper loss?

No. Copper loss happens in the transformer windings because of their electrical resistance. Eddy current loss happens in the core because changing magnetic flux induces circulating currents there. They are separate loss terms in a non-ideal transformer model.

### When does eddy current loss get worse?

It gets worse when the magnetic field changes faster, especially at higher frequencies. It also increases when the core material is thicker or more conductive, because those conditions make current loops easier to form. That is why transformer design has to match the operating frequency.

## Related Study Guides

- [7.3 Non-ideal transformer characteristics and equivalent circuits](/electrical-circuits-systems-ii/unit-7/non-ideal-transformer-characteristics-equivalent-circuits/study-guide/LtkPYr8pD30StXQo)

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