Download M2 : DC Machines

Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
M2 DC Machines
I.
Objectives
This Experiment aims to observing the operation ad characteristics of the:
1. Separately excited DC generator.
2. Shunt excited DC generator.
3. Shunt excited DC motor.
4. Series excited DC motor.
II. Background
Small DC machines (fractional HP) are used as control devices such as tacho-generator and
servomotors. Large DC machines are used in industry. A wide variety of volt-ampere or torquespeed characteristics can be obtained from various connections of the field windings. The DC
machine is extensively used as a motor in industry. Its speed can be controlled over a wide
range with relative ease. The most common speed control methods are adjustment of the flux
usually be means of field current control, armature current control and adjustment of the
armature terminal voltage.
III. Procedure
Test 1: The external characteristic of a separately excited DC generator
The experiment setup is as shown in Fig. (1)
1. Run the generator with the help of shunt motor at rated speed.
2. Switch on DC supply to the field winding of a separately excited DC generator and pass a
small current by changing the setting of the field rheostat.
3. Read the generator terminal voltage at different values of field current at constant speed.
4. Adjust the field rheostat to obtain rated generator voltage.
5. Close the resistive load switch and change the load of the generator with the help of
loading rheostat.
6. Read the load current and the terminal voltage.
7. Reduce the supply voltage to obtain another value of motor speed.
8. Repeat the above steps.
Test 2: The external characteristic of a DC shunt generator
1. Connect as shown in Fig. (2).
2. Run the motor and bring it to its rated speed.
3. Adjust the field resistance of the generator so that the generator builds up its rated
voltage.
4. Close the load switch and change the load of the generator.
5. Check the speed, adjust it to rated value, and record the load current and terminal
voltage.
6. Reduce load and field current gradually.
7. Switch off the load.
8. Stop the motor.
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
Test 3: The external characteristic of a DC shunt motor
1. Connect as shown in fig. (2).
2. At starting, a rated voltage is applied at the armature terminals. Increase the supply
voltage gradually until the motor builds up its rated speed.
3. Adjust the field rheostat of the generator to obtain rated voltage.
4. Load the generator, keeping its terminal voltage constant with the help of field rheostat.
5. Read the input voltage, current and speed.
6. Change the supply voltage and repeat the above steps.
Test 4: The external characteristic of a DC series motor
1. Connect as shown in fig. (3).
2. Set the generator field rheostat a lower value and keep suitable loading rheostat in the
circuit.
3. Switch on the DC supply and start the motor at reduced supply voltage.
4. At the time of starting, care should be taken, the generator builds up and is loaded to
some value so that the speed is within limit.
5. Adjust the field current of the generator to obtain rated voltage.
6. Change the load of the generator with the help of loading rheostat.
7. Read the input voltage, current and speed.
IV. Report
Test 1:
- Plot generator O.C. terminal voltage versus the field current at rated speed.
- Plot the external characteristic of the separately excited DC generator (VL – IL).
Test 2:
- Plot the external characteristic of the DC shunt generator (VL – IL).
Test 3:
- Plot the external characteristic of the DC shunt motor (n – IM) for several supply voltage
values.
- Plot the speed of the motor against the supply voltage.
Test 4
- Plot the external characteristic of the DC series motor (n – IM).
Discuss the above results and comment on the main points
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
Connection Diagrams
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
M2: DC Machines
Lab results
n=
1. Magnetization Curve
If (A)
0
E (V)
n=
2. Separately excited DC generator
IL ( Ia ) (A)
0
VL (V)
200
3. Shunt excited DC generator
n=
IL (A)
0
VL (V)
200
4. Shunt excited DC Motor
At Vs = 200 V
Ia (A)
n (rpm)
At Vs = 150 V
Ia (A)
n (rpm)
5. Series DC Motor
At Vs = 150 V
Ia (A)
n (rpm)
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
Magnetization curve
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
External characteristics of separately excited DC generator and shunt DC generator
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
External characteristics of DC shunt motor and DC series motor
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
Appendix of DC Machine Lab (M2)
A) Sample of rating plate of a DC motor (Siemens)
Where,
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
B) Sample of faults and its countermeasures
1. Faults in operation
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Faculty of Engineering
Cairo University
Electrical Power and Machines Dept.
Electrical Machines Lab
Third Year
M2: DC Machines
2. Commutator faults
C) Datasheet of a DC motor (Buhler Motor, Type: 1.13.063.xxx)
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STOCK SERVICE
DC Motor Ø 64
1.13.063.XXX
Design
1.13.063.XXX
Type 1.13.063.XXX
Commutator
Copper/12-segments
RFI Protection
2 chokes
Insulation class
Winding H, otherwise A
Protection class
IP40
Commutation
carbon brushes
Armature
straight slot
Magnet system
Permanent magnets, 2-pole
Bearings
2 preloaded ball bearings
Housing
Steel, corrosion protected
End shields
zinc die-cast on both sides
220
221
407
408
Characteristics*
Rated voltage
V
V
12
24
12
24
Rated power
PN
W
115
115
150
150
Rated torque
TN
mNm
350
350
400
400
Rated speed
nN
rpm
3150
3150
3400
3400
Rated current
IN
A
15
7.5
17
8.5
No load speed
nO
rpm
3700
3700
3900
3900
No load current
IO
A
2.6
1.3
2.0
1.0
Starting torque
TS
mNm
2500
2500
3400
3400
Starting current
IS
A
95
47
128
64
max. Output power
Pmax
W
230
230
340
340
max. Constant torque
Tmax
mNm
350
350
400
400
No load characteristics*
Starting characteristics*
Performance characteristics*
Motor parameters*
Weight
G
g
1300
1300
1600
1600
Rotor inertia
J
gcm2
850
850
1050
1050
Terminal resistance
R
Ohm
0.125
0.5
0.1
0.4
Mech. time constant
τm
ms
15
15
11
11
Electr. time constant
τe
ms
2.0
2.0
2.5
2.5
Speed regulation constant
Rm
rpm/mNm
1.5
1.5
1.02
0.98
Torque constant
kM
mNm/A
27
54
27
54
Thermal resistance
Rth1
K/W
2.8
2.8
2.5
2.5
Thermal resistance
Rth2
K/W
Axial play
Direction of rotation
3.3
3.3
3.0
3.0
< 0.1
< 0.1
< 0.1
< 0.1
bidirectional
Operational conditions
Temperature range
T
°C
-10 - +70
Axial force
FA
N
50
Radial force, 15 mm from mounting surface
FR
N
200
* at 25 °C
1.13.063.XXX
Customized versions
The following modifications are available upon request:
3
Encoder possible
3
Internal chokes and/or capacitors
3
Speed adjustment by winding change
3
Modification of shaft length on both ends
3
Modification of shaft configuration (flat, groove, etc.)
3
Assembly of gears, pinions, worms, etc.
3
Assembly of adapters and mounting plates
3
Reduced cogging torque possible