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Special Issue Article Open Access
Induction motors are the most commonly used machine in industry because of their robust nature. Energy management of induction motor is relevant as they form the bulk segment in industry. So online monitoring and efficiency estimation of the existing induction motors play a vital role in energy management. The air gap torque (AGT) method is a well established technique for determining the efficiency of an induction motor, since it is known to be highly accurate. However, it is considered to be too intrusive for industrial applications. To resolve this, nonintrusive AGT (NAGT) method is adopted here for efficiency estimation. The NAGT method measures only the motor terminal quantities and combines various estimation techniques to determine these parameters in a non-intrusive manner. Speed is measured by using tachometer. Stator resistance is obtained by DC signal injection method. No load losses are assumed empirically as a percentage of rated input power. Stray loss is estimated by a method similar to IEC Std 34-2-1. Modified NAGT method obtained by the above modifications is simulated and compared with efficiency curve obtained from load test and AGT method. Winding health estimation is done by using negative sequence current method with considerations to supply voltage unbalance conditions. Hardware implementation of the modified NAGT method and winding health analysis was also done.