What is the effect of a shorted turn in a stator winding?

• A. Increased overall machine efficiency.
• B. Localized heating, reduced output, increased losses, and possible insulation damage.
• C. Improved cooling efficiency.
• D. Decrease in reactive power demand.

Answer: (B)

A shorted turn in a stator winding creates a low-impedance loop within one phase. That means a circulating current flows in that small portion of the winding independent of the normal current path. The result is localized copper loss and heat right in that loop, often much hotter than the surrounding winding. This localized heating can heat adjacent insulation, leading to insulation damage or accelerated winding deterioration if not addressed.

Because part of the winding is effectively bypassed by the shorted turn, the machine’s ability to generate electromotive force is reduced, and the extra circulating current adds losses. Overall output drops and efficiency falls since energy is being wasted as heat rather than contributing to useful output. The increased current in the affected loop also tends to raise stray losses and can alter the current distribution, which typically means the reactive power demand does not go down—in fact, it can rise due to higher currents. That combination—localized heating, greater losses, and potential insulation damage—best matches the described effect.