ELECTRICAL ENGINEERING DEPARTMENT
THE CITADEL
EXPERIMENT # 302-108B
OPERATING CHARACTERISTICS OF
SHUNT AND COMPOUND DC GENERATORS
REFERENCES: 1. Appropriate chapters of ELEC 316 text.
2. Experiment No. 302-105B, DC Motor Configurations
OBJECTIVE:
The primary objective of this experiment is the determination of the terminal voltage versus load
current characteristic for the self-excited shunt generator and the self-excited cumulatively
compounded long and short shunt DC generators.
EQUIPMENT:
Power Supply Module
DC Motor / Generator Module
Synchronous Motor / Generator Module
DC Metering Module
AC Metering Module
Three-Phase Wattmeter Module
Resistance Module
Hand Tachometer
Timing Belt
Two DVM’s
NOTES:
This experiment involves the operation of rotating machinery. Prior to the application of
electrical power to any rotating machinery all machinery access covers must be closed. Prior to
opening any machinery access covers all electrical power is to be turned off.
EMS
EMS
EMS
EMS
EMS
EMS
EMS
EMS
EMS
8821
8211
8241
8412
8425
8441
8311
8920
8942
INTRODUCTION:
In this experiment, the synchronous motor will be utilized as the prime mover for all of the DC generators. The
synchronous motor will drive the generator at a constant speed under all of the load conditions of the experiment.
Figure 1 is a schematic diagram of the Synchronous Motor / Generator Module (EMS 8241).
During this experiment, the student should be comparing and verifying the experimental results with the theoretical
generator relationships.
PRIOR PREPARATION:
Prior to completing the prior preparation, refer to Figures 1 and 2 of this laboratory experiment and Figure 2 of
Reference 2.
Utilizing the EMS 8241 Synchronous Motor / Generator Module, Figure 1, the EMS 8441 Three-Phase Wattmeter
Module, Figure 2, and the EMS 8211 DC Motor / Generator Module, do the following for each of the three DC
generator configurations to be tested (the shunt connected DC generator, and both the long and the short shunt
cumulatively compounded DC generators):
1. Neatly draw a schematic and wiring diagram for each of the generator configurations to be tested. Each
generator is to be driven by a three-phase synchronous motor. The total input power to each system is being
monitored by the three-phase wattmeter. Include all meter placements in your diagrams.
PROCEDURE:
CAUTION: This experiment involves the use of high voltages and rotating machinery. Before applying any
voltages to any rotating machinery, ensure that all rotating parts are free from obstructions and that the front
access cover to the rotating machine is closed. Ensure that the voltage is adjusted to zero and that the power
supply circuit breaker is opened before making any changes to the circuit or to the motor configuration.
System no-load losses:
Do the following to determine the system no-load losses. These losses will be considered to remain constant
throughout all portions of this experiment. The determined no-load losses will be considered to be the system
friction / windage and core losses. Included in these losses will be the tachometer losses and the timing belt losses.
1. Connect the synchronous motor as it is connected in Figure 1, insure that the switch, ‘S’, on the synchronous
motor is initially open, in the down position. At this time do not connect the synchronous motor to the DC
generator under test. Once the synchronous motor is wired, turn on the power supply. After the motor starts
running, it should run in a CW direction – if not turn off the power and switch two of the phases of the threephase power supply- then turn the power back on. Once the motor is running in a CW direction, close switch ‘S’
(switch in the up position).
2. Adjust the synchronous motor rheostat for minimum synchronous motor input current (very close to the fully
CCW position). Leave the synchronous motor control knob in this position throughout this experiment.
3. Turn off the power to the synchronous motor. Place the switch ‘S’ in the open position (switch down). Using
the timing belt, connect the DC motor /generator module to the synchronous motor. At this time, do connect
any wires to the DC machine.
4. Connect the tachometer to the DC machine.
5. Once the DC machine is coupled to the synchronous motor, turn on the power to the synchronous machine.
Once synchronous motor is running close the switch ‘S’. This opening and closing of the switch ‘S’ is to be
done each time the synchronous motor is turned off and turned on. Now the synchronous motor is turning the
DC machine – no wires are connected to the DC machine. No power is being taken from the system. Therefore
all of the three-phase power in is power lost. This three-phase power will be designated as the system friction
/windage and core losses. Let the system run in this condition long enough to heat up.
6. Once the system has run long enough to heat up, record the system no-load losses and turn off the power. You
are now ready to test each of the three generator configurations. Do no change the synchronous motor
connections, and do not disconnect the timing belt.
Shunt Connected DC Generator
1. Connect the DC generator as a self-excited shunt generator. Ensure that the DC generator armature current,
shunt field current, and terminal voltage are each measured.
2. Turn on the power to the synchronous motor. Adjust the DC generator shunt field resistor for a maximum
resistance (fully CCW). Using the shunt field rheostat, vary the shunt field current from zero (open shunt field
circuit) to 0.4 A in 50 ma steps. Measure the following for each value of shunt field current (this is called the
magnetization characteristic of the shunt generator):
a. Shunt field current. b. Generator terminal voltage. c. Three-phase system input power.
3. Now adjust the shunt field rheostat for a no-load generator terminal voltage of 120 Vdc. Leave the rheostat in
this position for the remainder of this portion of the experiment.
4. Vary the generator load resistance through each of the following values: ∞ (open circuit), 600, 300, 200, 150,
120, 100, and 80 ohms. Make the following measurements for each value of the load resistance:
a.
b.
c.
d.
e.
Generator armature current.
Generator shunt field current.
Generator load current.
Generator terminal voltage (VT)
Three-Phase Input Power.
Long and Short Shunt Cumulatively Compounded DC Generators
Do the following for both the long and then the short shunt cumulatively compounded DC generators.
1. Connect the compound generator under test (long or short shunt). Ensure that the generator is cumulatively
compounded. How are you going to do this?
2. Open the shunt field circuit. Turn on the power to the synchronous motor and run the generator in this condition,
If = 0.0, and under no-load. Measure the no-load generator terminal voltage under these conditions, If = 0.0 .
3. Connect the shunt field circuit and adjust the shunt field rheostat for a generator no-load terminal voltage of
120 Vdc. Once this adjustment has been made, do not alter the position of the shunt field rheostat.
4. Vary the generator load resistance through each of the following values: ∞ (open circuit), 600, 300, 200, 150,
120, 100, and 80 ohms. Make the following measurements for each value of the load resistance:
a.
b.
c.
d.
e.
Generator armature current.
Generator shunt field current.
Generator load current.
Generator terminal voltage (VT)
Three-Phase Input Power.
REPORT:
Do the following for the shunt generator:
1. Plot the no load magnetization characteristic for the shunt generator (Ea versus If). Note, Ea is a calculated not a
measured quantity. How did you calculate Ea?
Do the following for each of the generators tested.
1. For each value of load resistance, calculate and tabulate the motor-generator system efficiency (for each value of
load resistance, identify and quantify all system losses).
2. For each value of load resistance, calculate and tabulate the synchronous motor torque developed and the
synchronous motor output torque.
3. For each value of load resistance, plot the generator terminal, load, voltage versus load current. Place each of
these generator plots on the same graph.
4. For each value of load resistance, plot the generated voltage, Ea, versus armature current. Place each of these
generator plots on the same graph.
5. Calculate the generator voltage regulation from no-load to full-load, 80 Ω.
4. Utilizing the results of this experiment, compare and contrast the operation of each of the three generators tested.
150Ω
1
4
S
4
2
5
5
3
6
6
7
8
8
120 Vdc
N
EMS 8241
Figure 1 Synchronous Machine
W
W
1 2 3
4 5 6
1
2
3
EMS 8441
Figure 2 Three Phase Watt Meter
A
4
A
5
A
6