Why Copper Wire Is Used In Transformer? Answered

There are multiple reasons Why Copper Wire Is Used In Transformer? Manufacturers and installers of transformers have been debating the advantages and disadvantages of copper versus aluminum wire windings for years.

Copper is frequently seen as being preferable to aluminum. This is due to house fires caused by improper termination of aluminum windings in the past. But a correct termination gets rid of that danger.

Winding wire, or magnetic or enameled round wire, is a term for a wire coiled into a coil after being coated with a thin layer of insulation. It is crucial in constructing transformers and other magnetic devices (such as inductors and motors).

While copper windings are used in many transformers, some also use aluminum. To assist readers in deciding which is better for their needs, we have compared the two below.

Why Copper Wire Is Used In Transformer?

Despite being heavier than aluminum cable, copper wiring is frequently employed to create smaller, lighter transformers. This is so because copper has higher electrical conductivity levels than those of aluminum.

Copper has a resistance that is 0.6 times greater than aluminum. Copper’s strong short-circuit resist qualities make it the material of choice for power transformer conductors.

Copper Wire Is Used In Transformer

As a result, an aluminum conductor’s cross-section must be 1.66 times larger than a copper conductor to exhibit the same resistance level. To carry the same load, an aluminum wound transformer must be significantly bigger than a copper wound one. Additional benefits copper wiring has over aluminum wiring include:

  • Lower losses and temperatures as a result of improved thermal and electrical conductivity
  • increased dependability of line and load connections
  • better manufacture because conductors with smaller sizes are typically simpler to handle

The Role Of Copper In Transformers

Any transformer must contain copper to enable effective and safe power flow between two circuits. The transformer’s core and winding are both made of copper. The type of transformer and its power rating influence how much copper is used in it. Generally, bigger transformers need more copper, whereas smaller ones need less.

For instance, a dry-type transformer with a power rating of 10kVA normally requires 20–30 kilograms of copper. In contrast, an oil-filled transformer with the same power rating may require roughly 50 kilograms.

The Role Of Copper In Transformers

When it comes to copper’s function in transformer construction, the copper wires offer an electric current with a low resistance channel, enabling the transformer to transmit energy from one circuit to another effectively.

Copper also has exceptional conductivity qualities, which make it the perfect material for transformer windings. Overall, copper is crucial to the construction of transformers. Its use impacts the transformer’s performance, efficiency, and overall cost.

The type of transformer and its power rating will determine how much copper is needed, with larger transformers needing more copper than smaller ones. Other materials are also employed to guarantee the transformer functions at its best, even though copper is a crucial part of the design.


Basic Physics

The passage of electric current in a closed coil positioned inside a fluctuating magnetic field is a fundamental tenet of electromagnetic induction. In turn, this current generates a second magnetic field. The conductors in the coil feel a force proportional to the product of the two field strengths because the two magnetic fields repel one another.

The primary coil’s current flow creates the primary magnetic field in a transformer. The secondary current is proportionate to the primary current, and as a result, so is the secondary magnetic field.

As a result, the forces that the coils encounter one another are inversely proportional to the square of the current. This indicates that the forces encountered by the windings under short-circuit situations are two orders of magnitude more than at rated currents.

These forces apply radially in core-type transformers, tending to compress a coil and shorten its axial length. The forces acting on the coil surface in shell-type designs are perpendicular to it and tend to narrow its radial breadth.

Error Modes

External short circuits can significantly reduce a power transformer’s reliability if it is improperly built and designed, even if there is no imminent internal failure.

Conductors can move about and stretch; coils can bulge, buckle, telescope, tilt, or rupture, and all of these things can cause the insulation to break and, as a result, inter-turn short circuits. Moving conductors and spacers can cause mechanical failures of the insulation. Supports for winding ends may fail.

Practice In Design And Manufacturing

The selection of conductor material is the most important factor in the design and production of power transformers to improve their short-circuit withstand capabilities because its mechanical properties, such as yield strength and modulus of elasticity, are crucial to performance.

Because of this, appropriate design practices, such as those used by ABB, use copper with a minimum yield strength of 90 N/mm2 at a 0.2% offset (i.e., stress greater than 90 N/mm2 would be necessary to induce a permanent strain of 0.2%).

For heavy-duty transformers with frequent short circuits, such as those used in arc furnaces, this number can reach 280 N/mm2 and higher. Good designers believe that the best method to guarantee great short-circuit withstand capabilities in power transformers is to utilize the proper quality of copper.

Copper-Based Energy Performance Improvement For Transformers

In most cases, higher copper content in transformers increases energy efficiency and lowers lifespan costs. The different expenses incurred over a transformer’s long lifespan can be broadly divided into acquisition, operation, and end-of-life costs.

The running costs, which mostly include the cost of energy losses in the transformer, are the most significant. As a result, the wise buyer will consider the transformer’s energy performance heavily while making judgments and won’t just rely on direct expenses.

Using larger core and conductor cross-sections, a lower loss core material, or a better conductor, such as copper, are the main alternatives open to transformer designers for enhancing energy performance.

This mix is continuously optimized by designers and producers depending on relative material costs at the time and the unique procurement conditions on energy performance. This explains why there are so many different transformer designs available.

Differences Between Aluminum And Copper Windings

While copper windings are preferred for some applications, most low and medium-voltage dry-type transformers use aluminum windings to transport energy. The following are some of the main variations between the two kinds:

Initial Expenses

Because aluminum is a relatively inexpensive material, it is initially less expensive than copper windings. Additionally, the price of aluminum has a history of long-term stability, making windings less expensive.

Historically, the beginning costs of copper have been more unstable than those of aluminum. Nevertheless, even though copper windings are typically more expensive, many professionals think they have longer-term advantages over their aluminum counterparts.

Running Costs

In dry-type transformers, aluminum windings often occupy a higher cross-sectional area than copper alternatives. Compared to older-model copper wound transformers, the larger design of the aluminum windings results in a lower current density, resulting in a descending rate of heat loss and more energy savings.

Typically, copper windings have tighter coils that can be adjusted for a lower current density. In contemporary designs, copper windings frequently outperform aluminum windings in terms of long-term operating cost-effectiveness due to improvements that allow for reduced copper winding heat loss.


Although copper and aluminum windings serve the same basic purposes for low and medium-voltage transformers, copper is more reliable than aluminum. Copper is a far more efficient conductor than aluminum, which has only 62% of copper’s electrical conductivity.

The equalization of the energy loss factors for each kind can be achieved through proper insulation. The windings’ size also impacts heat loss, and metal may be easily altered to address this problem. Nevertheless, because of its physical toughness and deformation resistance, copper typically offers higher long-term dependability.

Operating Life

Copper and aluminum windings’ working lifespan is comparable if installed and maintained correctly. Aluminum has the disadvantage of often being more difficult to install than copper, which can occasionally lead to operational problems that could have been avoided.

Copper is often a better alternative for protection against fault current strains and overall longevity, even though modern design advancements have enabled transformer professionals to overcome the technical issues connected with aluminum.


Did you get my point about Why Copper Wire Is Used In Transformer? You want an inexpensive metal that transmits electricity well for electrical circuits like transformers. Although incredibly effective, gold and silver should be pricier.

Aluminum is reasonably priced, but it burns down houses when utilized for a short period since it has a higher resistance than copper. Steel rusts and conducts electricity poorly. Copper is still the greatest option, although it is becoming increasingly pricey.

Frequently Asked Questions

Why are windings made of copper?

Because of its excellent conductivity and low price, copper makes a fantastic material for motor windings. Still, it is also quite dense and heavy, an issue for motors used in electric vehicles or aircraft, which must be lightweight.

What kind of copper do transformers use?

Copper OFHC is utilized in the transformer windings and the conductive paths of buck-boost transformers and dimmers. The high conductivity of OFHC copper guarantees these devices’ effective and reliable operation. At the same time, the low resistance of this material minimizes heat generation and lowers energy loss.

Why does copper work as a conductor better than aluminum?

Aluminum is approximately 30 percent the weight of copper but has 61 percent conductivity. Therefore, an aluminum bare wire with the same electrical resistance weighs half as much as a copper bare wire.

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