278 Copyright Goodheart-Willcox Co., Inc. Procedure 1. Before wiring the motor, check the winding resistance between T1 and T2, T1 and T3, T2 and T3. Record the resistance values. 2. Make the power connections to the motor. 3. Get permission from your instructor to turn on motor. 4. Set up the meter to measure LRA current. 5. Start motor. Record LRA for one phase (L1 for example). 6. Measure the operating current for all 3 phases and record. 7. Turn off the motor and observe shaft rotation. 8. Disconnect the power to lab station. 9. Exchange the L1 and L3 at motor terminals. 10. Get permission from your instructor to turn on the motor. 11. Turn on the motor. 12. Perform phase imbalance by measuring the voltage to the motor. Measure the three combinations T1 and T2, T1 and T3, T2 and T3. Record values. 13. Find the average of the three values by dividing the sum of the values by 3. 14. Find the maximum deviation from average. (Consider: combination differs more from the average and by how much?) Record value. 15. Apply the formula: phase unbalance % = max deviation × 100. average Lab Questions Use your digital multimeter or other electrical instruments to answer the following questions. 1. Was the resistance of the three combinations nearly equal? ______________________________________________________________________________________________________________ 2. What is the LRA? ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ ______________________________________________________________________________________________________________ 3. Were the operating phase currents nearly the same? ______________________________________________________________________________________________________________ 4. Did the shaft rotation direction change when L1 and L2 were exchanged? ______________________________________________________________________________________________________________ 5. Is the phase imbalance less than 2%? ______________________________________________________________________________________________________________