The circular coils in the transformer have the following advantages over rectangular form coils.
- The circular coil has a minimum mean length of the turn. If the diameter of the circular coil is d, the length of one turn πd. The length of the one turn of the rectangular coil is 2d. Thus, the circular coils have about 1/3 rd length in comparison with rectangular coils. The less length of the wire means the less ohmic value because the resistance of the wire is directly proportional to its length. The heat loss in the case of the circular coil is minimum.
- Under fault conditions, the coils of the transformer experienced heavy electromagnetic forces. The force act on the central axis of the coil. In a circular coil, the force is even throughout the coil, whereas the force on the rectangular coil is uneven and the force is maximum at the center and weaker at the edges of the coil. Thus, the rectangular coils are prone to damage under fault conditions.
- The winding of the circular coil is easy to form. There is a chance of insulation damage at the corners of the rectangular coils.
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