THE UNIVERSITY OF HONG KONG DEPARTMENT OF ELECTRICAL & ELECTRONIC ENGINEERING

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Cecil Greer
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1 THE UNIVERSITY OF HONG KONG DEPARTMENT OF ELECTRICAL & ELECTRONIC ENGINEERING Experiment MI1: D.C. Shunt and Series Motors Location: Objectives: Apparatus: Part I Laboratory To study the performance characteristics of d.c. shunt and series motors with speed control effected by varying the field current and armature voltage respectively. Motor (FH50 D.C. Compound Machine) under test and brake load Rheostats (FH2 MkIII Test Bed) D.C. voltmeter, ammeters and tachometer. D.C. supply (FH3 Mk III Instrumentation Frame) Measurement Interface and 12V DC Power Supply Computer with LabView data acquisition program Procedures: A. Shunt Motor Load Test 1. Position the FH50 Mimic Diagram over the access sockets of the FH2 MkIII Test Bed.Locate the test FH50 into the right-hand Test Position and insert the 10-way and earth plugs into their respective adjacent sockets. Set-up the equipment and connect as shown in the diagram. Figure A. Switch on the power to the FH2 MkIII Test Bed, first at the Main switch and press the Green ON push-button to activate the contactor. Start the motor by rotating the Armature Rheostat to zero and increase the brake control (torque control) until the motor develops an indicated torque of 0.5Nm. Allow the motor to warm up for approximately 15 minutes. 2. Turn on PC power until the LabView data acquisition program launch ( Click the desktop shortcut MI-Lab DAQ ).Switch on the D.C 12 Volt power supply for the measurement interface. Check all meters reading should be matched with LCD Monitor display. 3. Press save data button from computer and choose saving path as C:\Data\<your student id>\shunt.lvm for taking readings of voltage (kept constant at the rated value), currents and speed for roughly equal increments of load torque (0.05Nm ~ 0.8Nm)Do not allow the armature current to exceed 120% of the rated value. 4. Press the Save Data button again to stop saving data. 5. Repeat the load test (step 1 to 4) with the field current reduced (by adjusting the regulating resistance) to about 70% of the maximum value, choose saving path as C:\Data\<your student id>\shunt-2.lvm in step 3. N.B. During starting the shunt motor may take excessive current if the starting resistance is cut out rapidly. It is desirable to start with full field current or else the motor will not speed up as there is insufficient flux. The back e.m.f. will then be too low to oppose the applied voltage, resulting in excessive armature current.

2 B. Series Motor Load Test 1. Position the FH50 Mimic Diagram over the Machine Access Sockets of the FH2 MkIII Test Bed. Locate the test FH50 into the right-hand test cradle and insert the 10-way and earth plugs into their respective adjacent sockets. Set-up the equipment and connect as shown in the diagram. Figure. B. Switch on the power to the FH2 MkIII Test Bed, first at the Main switch and press the Green ON push-button to activate the contactor. Start the motor by rotating the Armature Rheostat to zero and increase the brake control (torque control) setting until the motor develops an indicated torque of 0.4 Nm. Allow the motor to warm up for approximately 15 minutes. Adjust the brake control (torque control) until the motor nearly stalls and then return it to minimum ( 0.05Nm ). 2. Turn on Computer power until the LabView data acquisition program launch ( Click the desktop shortcut MI-Lab DAQ ), then switch on the D.C 12 Volt power supply for the measurement interface. Check all meters reading should be matched with LCD monitor display. 3. Press save data button from computer and choose saving path as C:\Data\<your student id>\series.lvm for take readings of voltage, speed and current for roughly equal increments of load torque. Do not allow the current to exceed 120% of the rated value. The stall torque may be included in the range of values but the reading must be taken quickly before the overloads operate. DO NOT allow the motor to run without a load, minimum 0.05Nm, otherwise the rotor may seriously overspeed and could disintegrate. 4. Press the Save Data button again to stop saving data. 5. Repeat the load test (Step 1 to 4) for a reduced voltage supply of about 80% of the rated value and choose saving path as C:\Data\<your student id>\series-2.lvm in step 3. Copy you LabView data files from the path C:\Data\<your student id>\ to your USB flash memory/disk. Convert LabView file to Microsoft Excel file Choose Open File command from Microsoft Excel, select "files of type" to All Files (*.*) with "file name" to C:\Data\<your student id>\<filename>.lvm path. Click Open then a import Wizard will be shown. Choose Delimited radio button, start import at row as 1 then choose finish button. Choose File -> Save as command, select save as type to Microsoft Excel (*.xls) and change file name. N.B. A header information is shown for reference; other data will be shown after the header end. Reports: From tests (A) and (B), plot characteristic curves of speed, efficiency and armature current against torque. Also answer the following questions: (i) What is the effect on speed of the reduced field current for the shunt motor? (ii) What is the effect on speed of the reduced armature voltage for the series motor? (iii) Which of the above-mentioned motors are suitable for a). traction applications, b). driving lathes? Why?

3 A. Fill in numbers corresponding to the connection nodes in the photograph. Shunt motor wire connection Figure A

4 A. Shunt Motor Load Tests With Supply = V const. Field I f Torque T Nm Speed N r.p.m Arm I a Supply I=I f +I a Input Power V x I W Output Power T x ω W Eff η % ω = 2π N/ 60 rad/sec η = 100 Tω/ V I

5 B. Fill in numbers corresponding to the connection nodes in the photograph. Series motor wire connection Figure B

6 B Series Motor Load Tests With Supply = V const. Supply Volt V volts Torque T Nm Speed N r.p.m Current I I Input Power V x I Watts Output Power T x ω Watts Eff η % ω = 2π N/ 60 rad/sec η = 100 Tω/ V I

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