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Round Coil vs. Rectangular Coil for Transformers

Round Coil vs. Rectangular Coil

Substation transformers use round, rectangular or, less commonly, oblong core and coil assemblies. Coils facilitate the transformer’s magnetic flux flow. Coils and transformers work together to optimize performance based on design and application requirements.

The transformer’s core shape determines the coil type. In other words, round iron cores must use round coils and so on. But which coil configuration is better for dry type transformers? Understanding these differences encompasses their shapes, voltage capabilities, cooling abilities and cost-effectiveness.

Primary Differences of Round vs. Rectangular Coils

These two common coil shapes have distinct characteristics for various electrical applications, especially transformers. Under normal operating conditions, round and rectangular coils in dry type transformers behave almost identically. However, each type responds differently under abnormal conditions, such as a short circuit.

The physical differences between round and rectangular coils are straightforward. Another difference between rectangular and round coils in dry type transformers is the negative space within their core configurations. While circular core setups have slight air gaps between the magnetic flux-carrying steel and the windings, rectangular cores entirely fill this gap, resulting in fewer inefficiencies.

Round Coils

Advantages of Round Coils

Manufacturers often choose a round transformer coil for mechanical strength. Round or cylindrical coils can withstand radial forces while maintaining their circular shape. They have tiny air gaps between the magnetic flux that carries steel and windings. Here are more features that set this coil shape apart from the alternatives.

  • Cooling efficiency: A circular shape conducts better heat dissipation and allows the coil to cool more efficiently using insulating fluids like oil.
  • Easy manufacturing: Their simple winding process makes producing round coils easier and more cost-effective.
  • High-power capacity: Round coils have uniform current distribution and are well-suited for transformers that push high voltages.
  • Robustness: Thanks to their robustness and even heat dissipation, round coils are excellent for heavy-duty applications and operation in challenging environments.

Rectangular Coils

Rectangular or square coils, also known as layer or disc windings, feature four sides and slightly rounded edges. Constructed using flat conductors, they are layered and flat. Importantly, they handle radial forces less effectively than their circular counterparts, usually losing their rectangular shape during a short circuit. However, there are a few advantages to using rectangular transformer coils.

  • Space use: With flexible design options, rectangular coils allow for custom configurations that optimize space use in specific transformer designs.
  • Customization: These coils have more design flexibility to suit most layout requirements and space limitations.
  • Small transformer applications: Rectangular coils are more compact and suitable for low-voltage applications in smaller transformers.
Advantages of Rectangular Coils

Through-Fault Capabilities

Another noteworthy difference between round and rectangular coils lies in their ability to respond to through faults. A through fault happens outside the transformer zone. When the downstream components do not clear through faults, the transformer will overload and lose its ability to handle the sudden influx of electrical currents running through it. Round coils fare better because of their more uniform stress absorption. They feature fault protections that can reduce the risk of damage due to faults and similar occurrences. 

In through-fault scenarios, transformers with round coils tend to fare much better than those with rectangular coils because rectangular coils lose their shape when encountering short circuits. Even if the rectangular coil features restraining or “bracing” devices to help it maintain its shape, a short circuit will likely produce substantial damage. With their uniform stress absorption, round coils are better at handling through faults.

Applications in Dry Type Transformers

Dry type transformers transfer electrical energy between circuits by using electromagnetic induction created by transformer coils. They have primary and secondary coils wrapped around a magnetic core. The primary coil generates a magnetic field that induces the secondary coil’s current, which connects to the load. These transformers do not use a cooling medium, allowing them to use either coil type. 

The choice between round versus rectangular coils for dry type transformers comes down to the application. Considerations include space efficiency, mechanical integrity, cooling abilities and voltage applications. 

Contact ELSCO Transformers Today

Contact ELSCO Transformers Today

Round and rectangular coils have benefits to complement various transformer requirements. By design, each shape can optimize their applications’ efficiency, performance and space use. Choosing between these options depends on their voltage rating, space constraints, power capacity and manufacturing considerations. High-voltage transformers use round coils for efficient cooling, while smaller transformers may use rectangular coils for space-saving needs.

Turn to ELSCO Transformers for high-quality dry type transformers. Since 1912, we have provided customers across industries with expert guidance on selecting the correct transformer for their specific applications. Get a free quote when you contact us online or call 800-232-9002 for more information about our transformers today.

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