Lab Information
EXPERIMENT NO. 15
LOAD CHARACTERISTICS OF A THREE-PHASE INDUCTION MOTOR
PURPOSE:
To study the load performance of a squirrel-cage induction motor.
APPARATUS REQUIRED:
1. One IM-100 Induction motor
2. One DM-100 DC Machine as Generator
3. One SLA-100 Strobe-Tachometer
4. One Hampden AC Voltmeter
5. Two Hampden AC Ammeters
6. Two Hampden AC Wattmeters
7. Two Hampden DC Voltmeters
8. One Hampden DC Ammeter
9. One RL-100 Resistance Load
10. One 208V - 30 Power Supply
11. One 0 to 150 Volt/1 Amp DC Power Supply
PROCEDURE:
1. Couple the Induction Motor to the DC Generator and make the connections shown in Figure
30. Adjust the generator's rheostat to its maximum resistance, fully CW position. Adjust the 150
volt DC supply to 115 volts.
2. Have the instructor check your machine and meter connections. A shorting switch or jumper
should be placed across the current coils of the motor's meters to protect them from overload
during starting.
3. Start the motor and adjust the output of the generator to 90 volts DC by means of its field
rheostat.
4. Perform a load test on the motor from 1000 to approximately 1.0 amps load on the
generator's rheostat to maintain a 90 volt DC output. Record the motor's volts, amps, watts, and
speed and the generator's volts and amps.
5. For each load step, calculate the motor's volt-ampere input, total power input, and power
factor. Record the calculations.
6. For each load step, calculate the generator's output power. Record the calculations.
REPORT:
Plot the motor's input current, power, power factor, and speed as ordinates versus the generator's
output power as abscissa. Analyze your curves, comparing them to the results that one would
expect considering the theory involved.
QUESTION:
Why does a poly-phase motor start without special starting windings?
FIGURE 30