A novel efficiency improvement measure in three-phase induction motors, its conservation potential and economic analysis

This paper performs end-use energy analysis and estimates the benefits to India of a proposed efficiency improvement measure in three-phase induction motors. It was found that in a 3.7 kW motor, widely used in agriculture and industry, typical rewinding practice is associated with reduction in either winding conductor size by 1 SWG or reduction in number of turns per coil by one turn from the winding specification. This improper rewinding practice results in efficiency reduction by over 5 percentage points. Moreover, torque per ampere is decreased and higher temperature rise ensues. This is applicable to motors of all efficiency categories including energy-efficient designs. A method has been proposed to non-destructively determine the winding details without damaging the winding. This paper proposes a measure for efficiency improvement in improperly rewound motors of “standard” and energy-efficient designs as well as on “standard” motors that have not been rewound. The efficiency improvement measure essentially involves rewinding the motor taken up for efficiency improvement. The reduction in efficiency due to not-so-proper rewinding practices is also taken into account for the analysis. By means of this measure, the aforementioned performance deterioration can be reduced, if not removed entirely. The method will be of significance to India, where more than 50% of the operational motors are rewound motors and the majority of the rewinders are not well informed. Best practices to be followed during rewinding are also recommended. The conservation potential of the measure has been explored and economic analysis for implementation of the measure is provided. The payback period for the investment towards the proposed efficiency improvement measure by the industrial end-user for the 3.7 kW (5 HP) case is 1.3 years, if the motor is to operate for 24 hours continuously for 300 days. Suggestions have been made for the implementation of the efficiency improvement measure on an all-India level.