Lab Information -- Direct Current Machine Experiments
EXPERIMENT NO. 6
LOAD CHARACTERISTICS OF A SHUNT GENERATOR BELOW RATED SPEED
PURPOSE:
To study the load characteristics of self-excited shunt generator below rated speed and at rated
voltage.
APPARATUS REQUIRED:
1. One DM-100/A DC Machine as generator
2. One DM-100/A DC Machine as motor
3. One Hampden SLA-100D Tachometer
4. One 0 to 150 volt DC Voltmeter
5. One 0 to 1.5 Amp DC Ammeter
6. One 0 to .5 Amp DC Ammeter
7. RL-100/A Resistance Load
8. One 0 to 125 Volt/5 Amp DC Power Supply
PROCEDURE:
1. Couple the DC Generator to the DC Motor 6 and make the connections shown in Figure 1.
Adjust the generator's field rheostat- to its maximum resistance, fully CW position.
2. Have the instructor check your connections.
3. Start the motor and adjust its speed to 1650 RPM by slowly increasing the output of the 125
volts DC supply to bring the motor up to speed. Adjust the generator's output to maximum by
means of its field rheostat.
4. Perform a load test on the generator from no load to approximately 1 amperes load. It will be
necessary to adjust the 125 volt DC supply by means of the motor's rheostat, after each load step
is applied to maintain 1650 RPM. Record the armature volts, load current, field current, and
speed.
SUGGESTIONS FOR CONCLUSION:
Plot the armature voltage as ordinate versus the load current as abscissa.
QUESTIONS:
1. What would the effect on voltage regulation of operating the generator above rated speed at
rated voltage.
2. One might reason that it is always best to operate generators at reduced speed for better
regulation. Why is this not advisable?
FIGURE 6