Download Electric Motor Comparison Procedure

Updated 10/03/2008
Electric Motor Comparison
Apparatus
Figure 1: Electric Motor Comparison--Table 1
Figure 2: Electric Motor Comparison--Table 2
First you will need to locate the module in room 1B60. Make sure to acquire two carts, Figures
1 and 2, which should include:
 Cradled dynamometer (1 hp DC motor, rectifier, scale, resistors, tachometer)
 ½ hp 110 V AC motor
 ¾ hp 110 V AC motor
Figure 3 shows a schematic diagram of the dynamometer apparatus. The AC motor is the motor
that you are testing. Its current is measured with a current transducer (the black loop with a
wire through it) or the ammeter, and its power consumption is measured directly with the
power transducer or the kW-hr meter. The rectifier provides the DC current to the field coils of
the dynamometer motor. The heating coils and the lamps provide the resistive load to the DC
motor. The torque produced by the test motor is measured using a load cell or the scale.
Load
Cell
Lamps
kW-hr meter
Power
Transducer
(Current and
Ammeter Voltage)
Rectifier
24 V DC
110 V DC
Breaker Box
Scale
Switch
mA
Motor
Power Plug
Heating
Coils
DC motor
Tachometer
Rectifier
V DC
Motor
AC motor
Circuit 7
Rectifier
Power
Field Intensity
Board
DC volts
Hi Lo F1
F2
DC amps
GND
Circuit 6
Motor Power
Rectifier
Power Plug
Figure 3: Schematic diagram of a dynamometer and motor apparatus
Procedure
Safety: Persons operating rotating equipment must roll up long sleeves, remove neck-ties, and
secure any loose hair and clothing.
1. Plug the USB data-acquisition card (labeled “National Instruments”) into a USB port on
the front of the LabStation.
2. Open the NI Measurement and Automation Explorer (MAX) software. On the left side
of the screen within the Devices and Interfaces tree, a NI cDAQ-9171 device should be
listed. Make sure this device is labeled as “CDAQ1,” and if it is not, re-label it to be
“CDAQ1” (right click on the deviceRename). This is necessary for the LabVIEW
program to work properly.
3. Make sure that both the motor and the rectifier switches (breaker-box switches) are
OFF, Figure 4a. The field-intensity dial (labeled “Increase Field”) of the dynamometer
should be turned completely counterclockwise. If a load is applied before the motor
has reached operating speed, the system will overload and blow a fuse.
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Rectifier
Socket
Motor and
Rectifier
Switches
a)
Field-Intensity Dial
Rectifier Plug
b)
Figure 4: Make sure to connect the rectifier plug, turn the field-intensity dial fully counterclockwise and plug in the
rectifier to the dedicated rectifier socket.
4. Connect the yellow, three-prong plug from the rectifier to the field-intensity board,
Figure 4b.
Safety: Be sure to attach rectifier wires to the “field-intensity board” before plugging in the
rectifier.
5. Plug the power cord for the rectifier into the socket marked “Rectifier” behind the AC
motor, Figure 4a.
6. Next, plug the two 110 Volt power plugs leading to the breaker box into different
circuits at the lab station. In order to make sure the two plugs are on different circuits,
plug one connector into Circuit 6 and the other connector into Circuit 7, Figure 5. Both
are on the side of the LabStation next to the CPUs.
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Circuit 7
Circuit 6
Figure 5: Power Source
7. Zero the pound scale by turning the screw on the top of the load cell (be sure the turnbuckle does not rotate), and zero the ammeter with the screw at the center of the dial.
A screwdriver is in the drawer of the green cart.
8. Open the “ElectricMotorComparison” VI via the shortcut in the Electric Motor
Comparison folder within the ITLL Modules folder.
9. Set the voltage toggle switch, located on the rectifier, to 110 VDC and turn ON the
breaker-box switch for the rectifier.
10. Start the VI and zero the load within the VI by pressing the zero-load button. Note that
the rectifier switch must be on for the load cell to get power.
11. Record which motor is coupled to the generator (½ hp or ¾ hp). Verify that a
polyurethane bushing is placed between the couplings of the generator and motor
before proceeding. Secure the motor to the table with all four hex bolts if the motor is
not already secured (an allen wrench is in the drawer of the green cart).
12. Plug the motor into the outlet below the Motor Circuit Breaker switch. Turn the
breaker-box and motor-circuit-breaker switches ON and allow the motor to warm up
for at least five minutes. Make sure there is no load being applied to the motor (load
selector should be set to off) and the field-intensity dial should be turned fully
counterclockwise.
13. Save 10 seconds of data to your “Z:” drive using the Save Data button on the VI. The VI
saves the following data:
a. Tachometer counts and the associated time for the counts in 0.1 second
intervals (notice that these two columns are much shorter than the other four
columns of the data file because the time interval is much larger for the
tachometer data than for the load, voltage or current data),
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b. Voltage and current values (and time) for 0.001 second intervals.
c. Load from the load cell and the associated time values for 0.001 second
intervals,
14. Flip the load switch on the field-intensity board of the dynamometer to high. Do NOT
turn on the switch for the lights.
15. Adjust the field intensity with the field-intensity dial until the indicated force on the
scale and in your VI is about 0.25 lb.
Note: The field-intensity dial varies the applied load to the motor. When turned fully
counterclockwise, no additional load is applied to the motor regardless of the position of
the load switch.
16. Save 10 seconds of data.
Note: After adjusting the field-intensity dial for every load setting, wait at least 10
seconds before pressing the Save Data button in the VI. If the Save Data button is
pressed before 10 seconds lapses, the data saved will include incorrect data from the
previous load setting.
17. Turn ON the light switch.
18. Increase (or decrease) the field intensity to set the load to 0.50 lb, and save 10 seconds
of data.
19. Continue to increase the load level in 0.25 lb increments, saving data at every load
level, until the maximum attainable load is reached for the high-load setting. The light
bulbs should illuminate at higher load settings.
20. After collecting data for all load settings, decrease the load to zero (turn the fieldintensity dial fully counterclockwise), turn the light switch OFF, and turn OFF the motorcircuit-breaker switch and the motor and rectifier breaker-box switches.
21. Unplug and remove the motor by loosening the four bolts in the aluminum plate. DO
NOT REMOVE THE MOTOR USING THE BOLTS AT THE BASE OF THE MOTOR!
22. Mount the other motor to the dynamometer. Caution: A polyurethane bushing must be
placed between the couplings of the generator and motor! Use the gold-colored guide
pins to align the motor and then secure it to the table with all four bolts using an allen
wrench.
23. Repeat entire procedure with the new motor beginning on step 7.
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Safety: Do not touch bare wires of rectifier. Be sure to turn OFF the all breaker-box switches
when finished with the experiment and to unplug the rectifier power cable before removing
wires from the “field-intensity board.”
24. Turn OFF all switches and remove cables. Return apparatus to module bay. Return all
equipment that may have been checked out.
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