Chapter 6 Electromechan e r m m c a a ni cal a S Sy s st ems e s 1499 Copyright Goodheart-Willcox Co., Inc. Copyright Goodheart-Willcox Co., Inc. Procedure 1. Construct the ac synchronous motor test circuit shown in the following fi gure. fi Ensure that the motor is mounted securely. 2. Turn on the switch for clockwise rotation. 3. Momentarily turn on the power switch and observe the rotation of the motor. 4. With a tachometer, measure and record the speed of rotation. 5. Momentarily turn off the power switch and observe the stopping action of the synchronous motor. You may want to run several trials to see the quickness of the stopping action. How does this compare with other ac motors? 6. Note each time that the motor is turned on, how quickly it comes to speed. 7. With an ac ammeter, measure and record the running current and starting current of the synchronous motor. 8. Carefully wedge a piece of wood between the rotating shaft and the bench while holding the motor. This will provide a simple loading method for test purposes. 9. When the motor is loaded down, how does the running current respond? 10. If the motor is completely stalled, how does the running current respond? 11. Remove the load from the motor, turn off the clockwise switch, and turn on the counterclockwise switch. The motor should rotate equally well in the counterclockwise direction and have the same basic characteristics. Test these again to verify the theory. 12. Switch off the counterclockwise switch, then switch on the clockwise switch. Notice the ease with which direction change occurs. 13. Turn off the ac power source and disconnect the circuit. Return all parts to the storage area. Analysis 1. Discuss the operation of an ac synchronous motor. 3 2 1 Isolated ac source 120 V/60Hz AC synchronous motor Power switch CW switch 250 Ω 25 W R1 C1 3.75 μF 330 Vac CCW switch Goodheart-Willcox Publisher AC synchronous motor test circuit.