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How Low-Loss Electrical Steel Laminations Improve Motor Efficiency
When we list the factors that determine an electric motor's efficiency, the first things that usually come to mind are winding quality or the size of the motor. Yet the lamination stack that forms the magnetic heart of the motor, that is the thin steel laminations from which the stator and rotor are made, has perhaps the most decisive effect on efficiency. The material, thickness and coating of these laminations directly determine how much energy the motor wastes. At DRG Motor, this article explains in detail how low-loss electrical steel laminations raise efficiency in our IE3/IE4/IE5 efficiency-class asynchronous motors, how core losses form, and why choosing quality laminations matters so much.
What Is the Lamination Stack and What Does It Do?
The stator and rotor of an asynchronous motor are not a single piece of cast metal. Instead they are made of a stack formed by pressing thin steel laminations on top of one another. These laminations are called the lamination stack or core. The magnetic field created by the windings concentrates within this steel core and is transferred to the rotor.
The job of the core is to carry the magnetic field with the least loss and the highest density. Steel is very suitable for this task, because it conducts the magnetic field far better than air or plastic. However, while carrying the magnetic field, steel also produces two kinds of loss, and the most important struggle of motor engineering is to reduce these losses. You can find the basic working principle of motors in our what is an electric motor content.
Core Losses: Two Enemies Arising from the Iron
The losses that form in the lamination stack are called core losses or iron losses. These losses appear the moment the motor is energised, even if it draws no load, and continuously turn into heat. Core losses arise from two main mechanisms: hysteresis loss and eddy-current loss. Understanding these two is the key to grasping why some laminations are far more efficient than others.
If you want to examine the full set of losses in a motor, our electric motor efficiency losses content addresses the subject from a broader perspective.
What Is Hysteresis Loss?
When steel is exposed to a magnetic field, the magnetic regions inside it orient themselves to that field. When the field changes direction, these regions must reorient. Because in a motor fed with alternating current the magnetic field changes direction dozens of times per second, this reorientation is constantly repeated.
At each change of direction, some energy is spent to realign the magnetic regions, and this energy is lost as heat. This loss is called hysteresis loss. The way to reduce hysteresis loss is to use a special steel in which the magnetic regions can orient more easily; the silicon addition comes in exactly at this point.
What Is Eddy-Current Loss?
The changing magnetic field induces a voltage not only in the winding but also in the steel core itself. Because steel is a conductive material, this induced voltage circulates small circular currents inside the core. These unwanted currents are called eddy currents.
As eddy currents circulate inside the core, they meet the resistance of the steel and turn into heat, creating energy loss. The larger these currents, the greater the loss. There are two basic ways to reduce eddy-current loss: increasing the electrical resistance of the steel and narrowing the path the currents can circulate in. Both form the basis of lamination design.
Why Is Silicon Added?
Using silicon-alloyed steel instead of pure steel has two major benefits. First, silicon significantly increases the electrical resistance of the steel. As resistance rises, eddy currents circulate more difficultly and eddy-current loss falls. Second, silicon improves the magnetic properties of the steel, also lowering hysteresis loss.
For this reason motor cores use not pure steel but specially prepared silicon electrical steel. The silicon ratio is carefully adjusted; because too much silicon makes the steel brittle and harder to process. The right composition strikes the best balance between low loss and manufacturability. This balance is an engineering decision requiring experience and the right material choice; every excessive option increases either the loss or the manufacturing difficulty.
Thin Laminations: The Importance of Thickness
One of the most effective ways to reduce eddy-current loss is to build the core from thin laminations rather than a single piece. The thinner the laminations, the narrower the path for the eddy currents that can circulate inside, and the weaker these currents become. This is why in quality motors the core is made of many thin laminations insulated from one another.
Thick laminations are cheaper and easier to produce, but eddy-current loss is high. Thin laminations, though laborious to produce, markedly reduce the loss. For this reason lamination thickness is one of the most important design decisions determining a motor's efficiency class. Thinner laminations are preferred in motors targeting high efficiency. Using thin laminations requires more lamination layers, more precise pressing and more careful workmanship in production; this explains why the manufacture of high-efficiency motors is a more meticulous process.
Insulating Coating: Separating the Laminations
For thin laminations to reduce eddy currents, one condition must be met: the laminations must be electrically insulated from one another. If the laminations touch and make electrical contact, the eddy currents circulate throughout the whole stack as if it were a thick block, and the benefit of using thin laminations is lost.
For this reason each lamination is covered with a thin insulating layer. This coating prevents current passing between the laminations, turning each lamination into a separate magnetic path. A quality, properly applied coating fully reveals the efficiency advantage of the thin-lamination design. A coating that deteriorates or is damaged increases the loss and makes the motor less efficient than expected.
The Effect of Lamination Quality on the IE Efficiency Class
A motor's efficiency class is directly related to its core losses. Of two motors with the same design, the one using lower-loss laminations is always more efficient. Moving from an IE3 class motor up to the IE4 or IE5 class largely comes down to reducing core losses.
To reach higher efficiency classes, the manufacturer uses thinner, higher-silicon and better-coated laminations. This lowers the energy the motor wastes even while running unloaded and raises the total efficiency. Reading the IE class on the motor nameplate actually means seeing a summary of this loss level. For the contribution of efficient motors to the business, you can also review our high efficiency electric motors content.
Core Loss Exists Even at No Load
The most important feature of core losses is that they exist even when the motor draws no load. While the motor is merely connected to the mains, even doing no work, the core losses continuously turn into heat. This is especially important in motors that run long hours but with variable load.
In a motor that spends much time at low load, core losses make up a significant part of total consumption. For this reason low-loss laminations save energy not only at full load but across the motor's entire operating range. This continuity makes the investment in quality laminations more than worthwhile in the long run. Because in most businesses motors run for the greater part of the day, even a small improvement in core loss turns into a notable annual energy saving.
The Relationship Between Lamination Quality and Heating
Because core losses turn into heat, a motor using quality laminations heats up less. A lower operating temperature extends the life of the winding insulation and increases the overall durability of the motor. Low-loss laminations therefore directly affect not only the electricity bill but also the life of the motor.
A cooler-running motor is also quieter and needs less maintenance. Because heat is the greatest enemy of both insulation and greases; as temperature falls, these materials keep doing their job far longer. For this reason lamination quality is a holistic design element affecting several benefits at once, such as efficiency, life and comfort. Considered together with insulation class, it becomes clearer how integrated the motor's thermal behaviour is.
The Role of the Manufacturing Process
Choosing the right material alone is not enough; how the laminations are processed also affects the loss. The mechanical stresses created during cutting and pressing of the laminations can degrade the magnetic properties at the edges, increasing the loss. A careful manufacturing process minimises these adverse effects.
Proper alignment of the laminations, tight pressing of the stack and an undamaged coating ensure that the low-loss potential offered by the material is fully realised. For this reason, when quality laminations and quality manufacturing come together, the real efficiency advantage emerges.
The Balance of Cost and Value
Low-loss silicon laminations are more expensive than standard laminations, and this is reflected in the upfront price of higher-efficiency-class motors. However, this difference is recovered in a short time by the energy savings the motor provides over its working life. Especially in continuously running high-power motors, the savings brought by quality laminations far exceed the initial cost difference.
For this reason, in motor selection one should look not only at the price tag but at the total cost of ownership. Low-loss laminations are the most profitable choice in the long run. A motor's purchase price usually makes up a small part of the total life-cycle cost; the real major item is the electricity the motor consumes over the years. For this reason a few points of efficiency difference can, over time, turn into savings far above the purchase price on a continuously running motor. To make the right decision, the motor's daily running time and electricity unit price must be evaluated together.
Efficiency Is the Result of a Whole
Low-loss laminations are not the only determinant of motor efficiency; but they are one of its most fundamental cornerstones. A motor's total efficiency is made up of the sum of many components, such as core losses, copper losses in the winding, friction and ventilation losses. Reducing each of these losses requires a separate design effort. However, because core loss exists continuously from the moment the motor is energised, it is one of the first items to address. When the copper winding quality on the winding side and the lamination quality on the core side are improved together, the motor can reach the highest efficiency class. So real efficiency is the result of every detail, from material to workmanship, coming together in harmony.
Magnetic Density and Saturation
A steel lamination carries the magnetic field efficiently up to a certain point. But when the field rises too high the steel approaches its saturation point; beyond this point much more energy is needed for the same increase in field, and losses grow rapidly. Quality silicon laminations stay efficient up to higher magnetic densities, delaying the losses brought by saturation. This means the motor can produce more torque at the same size, or deliver the same torque with less loss. Saturation behaviour is an important measure of the quality of the lamination material and directly affects the motor's power density.
The Effect of Frequency on Core Loss
Core losses depend on how often the magnetic field changes direction, that is on the frequency. As frequency rises, both hysteresis and eddy-current losses grow; eddy-current loss in particular increases much faster with frequency. For this reason, in variable-speed applications, that is where the motor is driven at high frequencies by a frequency inverter, low-loss laminations become even more critical. A thin-laminated, high-resistance core keeps losses under control at high frequencies. So in modern drive-fed systems, lamination quality matters more than in fixed-speed applications.
Stator and Rotor Cores Are Considered Together
Core losses form not only in the stator but also in the rotor. While losses in the stator are pronounced at the supply frequency, in the rotor they appear in a different form depending on the slip frequency. An efficient motor design addresses both the stator and rotor cores together and considers the benefit of using low-loss laminations in both. The harmonious operation of the two cores ensures the magnetic field in the air gap is transferred cleanly and efficiently. This holistic approach creates a greater improvement in the motor's total efficiency than the sum of the individual components.
An Invisible but Decisive Component
When examining a motor from the outside you cannot see the lamination stack; it is hidden inside the body, beneath the windings. For this reason lamination quality is often overlooked in the purchase decision. Yet this invisible component determines a significant part of the energy the motor will consume over its life. Two motors can look identical from the outside, can be of the same power and speed; but if the laminations inside them differ, their energy consumption over the years diverges significantly. For this reason a conscious buyer looks not only at the external features but also at the motor's efficiency class and the core quality behind it.
DRG Motor for an Efficient Core and a Lower Bill
Low-loss silicon electrical steel laminations are the component that most deeply affects a motor's efficiency yet is invisible from the outside. At DRG Motor, we offer our IE3/IE4/IE5 efficiency-class asynchronous motors with a low-loss core structure and careful manufacturing. To determine the most suitable efficiency class to lower your facility's energy bill, explore our electric motor products and reach our technical team via drgmotor.com. To understand efficiency in more depth, you can also read our high efficiency electric motors and industrial electric motors content.
