Lab Information -- Direct Current Machine Experiments
EXPERIMENT NO. 8
SERIES GENERATOR OUTPUT POLARITY AND BUILT-UP
PURPOSE:
To study conditions necessary to cause build-up in a series generator.
APPARATUS REQUIRED:
1. One DM-100/A DC Machine as Generator
2. One MFM-100 Multi-function Machine
3. One 0 to 150 Volt DC voltmeter
4. One 0 to 1 AMP DC Ammeter
5. One Resistance load RL-100/A
6. 120 Volt AC Power Source
PROCEDURE:
1. Couple the DC generator to Multi-function Machine and make the connection shown in Figure
8. Make sure power supply is in OFF position
2. Have the instructor check your connections and then start the motor.
3. With series field disconnected, measure the DC voltage across the armature terminals and
record the magnitude and polarity of this voltage.
4. Observe the direction of rotation and record it. Notice: Consider the direction of rotation as
viewed from the outboard end of the generator.
5. In series connect the series field and resistance load across the armature terminals. Switch on
several steps of the resistance load. If the generator voltage rises, the correct connections have
been made. If the voltage decreases, reverse the series field connection and proceed.
6. Record the direction of rotation, connections, and the armature polarity.
7. Stop the motor and reverse the direction of rotation by swapping the connections to the
starting winding. With the series field disconnected, measure the DC voltage across the armature
terminals for this direction of rotation. Record the magnitude and polarity of this voltage and also
direction of rotation.
8. In order to cause the generator to build-up with this direction of rotation, it will be necessary
to reverse the series field connection from that of step 5. Make this connection, operate the
generator as in step 5 and record the connections and the armature polarity.
REPORT:
Using the data obtained for each connections make a table so it would include the direction of
rotation, polarity, voltage and connections.
QUESTION:
What conditions are necessary to cause voltage build-up in a series generator?
FIGURE 8