Circular Vs. Rectangular Windings | Part 1

March 11, 2014

Solomon Corporation is one of the largest independent providers of remanufactured and repaired substation transformers in the U.S. The engineers and technical support staff that make up the team at Solomon Corporation are experienced and knowledgeable about most manufactures and designs of substation transformers in the industries we serve. As a result, the transformers we provide our customers in the commercial, utility, and industrial industries can be custom-built to unique specifications. Our customers have relied on our well-engineered products for over 40 years, and our liquid-filled, substation transformers have been an ideal choice in the industry.

A substation transformer is a critical component in an electrical distribution system, where incoming high voltage transmission and distribution power is converted to the desired output voltage. Unlike more common distribution padmount transformers that are often used in lower-voltage commercial applications (such as those used by the fast-food industry to deliver power to their restaurants), substation transformers are considered to be more durable. The average substation transformer has an expected service life of 30+ years. And considering that substation transformers are constantly dealing with adverse conditions from system faults, large motor starts, rectifier and inverter duty, and other industrial applications, each is designed and manufactured to handle enormous radial and axial forces.

The magnetic circuit is one of the most important parts of a transformer and it consists of a laminated iron core which carries flux linked to the windings. The type of iron core determines the shape of the transformer coil or windings.  A substation transformer core and coil assembly can be described as having one of two types of windings: circular or rectangular. These two types of assemblies are very different in construction. They are also different in how they perform during short-circuit stresses. For substation transformers larger than 5,000kVA or industrial applications which have loads that require more rigorous duty, a circular core and coil assembly is more common. A rectangular core and coil assembly is used in transformers 5,000kVA and smaller, with standard distribution types of loads.

A substation transformer needs to be designed to handle the thermal and mechanical forces associated with short circuit forces without any deforming or changing the shape of the coils-which can lead to a transformer failure. During a short circuit or fault on a transformer, the mechanical forces on the transformer coil can be 250 times greater than those of normal operating conditions. These forces can be both radial and axial, which can damage the coil if it is not properly design to handle the mechanical stresses.