Power transformers play an important role in many electronics and electrical applications, each of which has distinct performance requirements. When designing a transformer, wire selection is one of the most important considerations. Round and flat wires each offer unique benefits and drawbacks for certain applications. Below, you can learn more about the characteristics of flat wire vs. round wire to help you determine the best option for your needs.

What Is Round Wire?

Round wire has a round cross-section and is the most frequently used type of wire. It is produced using two components: a round conductive wire material and an insulation layer that covers it. Also called overcoating, the insulation is a type of varnish made from a polymer film, such as:

• Polyglass
• Polyamide
• Polyester

These materials not only protect the wire but also allow coils to feature numerous turns without  shorted windings.

What Is Flat Wire?

Flat wire has a rectangular or square cross-section that offers unique benefits not possible with round wire. It is manufactured by rolling or drawing a metal like copper, aluminum, or stainless steel through a series of dies. The resulting wire is thinner than round wire of the same width, which makes flat wire more flexible and easier to shape. Compared to round wire, flat wire features a larger contact area, which is a valuable asset to applications where space is limited. Flat wire is used not only in transformers but also in inductors and many other electrical components.

What Is the Skin Effect?

Wire design plays an important role in how efficiently transformers are able to transfer energy. When electrical current passes through the wire in a transformer, it generates a magnetic field. Quickly changing magnetic fields cause the electrical current to flow along the wire's surface, or "skin," rather than throughout its entire internal diameter. This is referred to as the skin effect.

When round wires are used, even those with large diameters, the skin effect limits the amount of current that is carried. This can result  in inefficient performance since only a small amount of the wire's inner surface area is used. The current-carrying cross-section area in round wires is small, and as frequencies increase, the skin effect intensifies, further decreasing the utilized cross-sectional area. Flat wire in transformers, on the other hand, offers a larger surface for electricity to flow through, reducing resistance and allowing electrical current to travel more efficiently.

What Is a Better Choice for Transformers?

When comparing a single strand of flat wire vs. round wire, consider factors like conductivity and cost to select the best choice for a given transformer.

Round Wire

Round wire is the traditional option for transformers. Compared to flat wire, it is more cost-effective to produce and offers the best efficiency at frequencies up to 20 kHz. However, at higher frequencies, the skin effect increases the wire’s AC resistance.  One method to overcome these limitations is to twist or braid multiple strands of smaller round wire creating what is commonly known as Litz Wire.

Flat Wire

Compared to round wire, flat wire provides superior performance, with a higher energy storage and thermal efficiency. Due to its  unique design, flat wire provides as much as 60% more surface area than a round wire with the same cross-section area. This limits the skin effect at higher frequencies, leading to more efficient performance. Since flat wire provides a larger surface area for current to flow, it's possible to create higher current solutions with low parasitic capacitance.

However, there are a few drawbacks to flat wire. It tends to be more costly to manufacture than round wire, which can be a concern for some applications. It's also less widely available and can be challenging to source in certain materials or sizes. In certain electrical applications, flat wire may offer lower conductivity than traditional round wire.

Learn More About Transformers With Triad Magnetics

Transformer design is complex, but Triad Magnetics offers simple and reliable solutions. Our engineers have decades of experience in the transformer industry and can help you identify the best type of wire for your project. We work with an extensive range of high-quality materials and stock thousands of standard parts. Whether round wire or flat  wire is the right option for you, our team can source it in the correct size and material for your needs.

To learn more about transformers and proper wire selection, contact us with any questions. Request a quote to get your solution started.