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Explain the following Energy conservation methods of electrical motor : (a) Rewinding of motors (b) Operating in star mode
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Energy conservation methods of an electric motor: 

(a) Rewinding of motors: i) During rewinding by preserving the original winding characteristics (material quality, design and structure). It is possible to maintain the original operating characteristics. ii) Using larger cross-section area of conductors and better insulation the copper losses can be minimized. iii) Rewinding for the required torque and power or speed results in lowering of the losses (better efficiency and hence energy savings) iv) Extension of coils beyond the slot insulation must be minimized to reduce the amount of copper used that leads to lowering of the copper losses.

(b) Operating in star mode: i) Lesser than 30% load means torque required by load is less than 30%. Hence current requirement is reduced. ii) When connected in star, the phase voltage reduces to (1/3) times that in delta mode. As the torque generated by motor is directly proportional to the (applied voltage per phase)2 the torque produced falls to 1/3(which is requires) compared to delta mode. iii) Due to decreased phase voltage the iron losses decrease to nearly 1/3(as total iron losses are proportional to (applied voltage per phase)2 before saturation. iv) Due to reduction in phase voltage the current drawn in the lines also reduces leading to lower copper losses in motor and decrease line losses.

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