EXPERIMENT 1:
Part A
Shunt Wound Machine as Generator
: Connection and Starting
Objectives:
1. Connect and operate a D.C shunt wound machine as a self-excited shunt
wound generator
2. Deduce from the measurements that the magnitude of the generated voltage
is determined by the speed and the armature or exciter current
3. Explain the function and purpose of the field regulator
Circuit Diagram
t
s
RF
RB
IA
A
q
V
IE
A1
A
E1
E2
G
A2
PE
Fig 1.1a
1
L1
I
0
DANGER 415 Volts
ROTATION REVERSING SWITCH
1
L3
0
V
W
L2
2
U
L1
L2
L3
MOTOR PROTECTION SWITCH 3 POLE
I
L1 L2 L3
2
TORQUE
Nm
min -1 X 1000
M OL n
x1 x2 x3
CONTROL UNIT FOR MAGNETIC POWDER BRAKE
CONTR. MODE
BRAKE
MOTORS
min-1
REVOLUTIONS
0
Nm
SET/START VALUE
0
A1
E1
A2
E2
POWER
t
A2
M/G
A1
E1
q
s
SE2662-3A
E2
FIELD GENERATOR
Ω
W2
U1
U2
V1
V2
W1
LOAD RESISTOR
Ω
U2
U1
SE2662-3G
M
V2 W2
V1 W1
L1
L2
L3
PE
2 0 1
U1
V1
W1
W2
U2
V2
Fig. 1.2
3
Instrument/Component
1 D.C shunt wound machine
1 Three-phase asynchronous motor with squirrel-cage rotor.
1 Magnetic powder brake
1 Control unit for brake
2 Rubber coupling sleeves
2 Coupling guard
1 Shaft end guard
1 Field regulator for D.C generators
1 Load resistance
1 Motor protection switch
3 Multimeter
1 Set of connection cables
Exercise
1. Connect the circuit diagram shown in fig. 1.1a and fig. 1.1b
2. Connect the 3 Phase asynchronous motor shown in fig. 1.2
3. Couple the generator in fig. 1.1 to the 3 phase asynchronous motor
connected in step 2
4. Set the control unit as follows:
a) Speed
n
b) Torque
M
c) Operating mode n
= 3000 rpm
= 1Nm
= constant
Range on multimeters
a) Voltage
b) Armature current, IA
c) Exciter current, IE
= 300 V
=1A
= 0.3 A
Set the field generator to 0 % and the load resistance to 100% (~1000 Ω)
5. Operate the generator. Apply a load to the drive machine to obtain 2900 rpm
(or at maximum rpm obtained. Use set/start value from the control unit and
set it to fully clockwise)
6. Measure the generated voltage VG, the exciter current IE, and the armature
current IA, as given in the Table 1.1 below. The measurement must be
completed as quickly as possible.
4
N (rpm)
2900
2800
2700
2600
2500
2400
2300
2200
2100
2000
1900
VG (V)
IE (mA)
IA (A)
Table 1.1
Questions
1. What is the effect of reduction in speed?
2. What is the purpose of the field regulator?
3. What function has the load resistance?
5
Part B
: Load Characteristics
Objectives
1. Connect and operate a D.C shunt wound machine as a self-excited shunt
wound generator for recording the load characteristics
2. Measure the armature current when the load is varied
3. calculate the delivered electrical power
4. Draw the load characteristic curve
5. Deduce from the measurement that the delivered power has as almost linear
rise to a maximum, but drops off sharply when the load is further increased
IA
RB
A
A1
E1
E2
V
G
A2
PE
Fig. 1.3
6
Instrument/Components
1 D.C shunt wound machine
1 Three-phase asynchronous motor with squirrel-cage rotor.
1 Magnetic powder brake
1 Control unit for brake
2 Rubber coupling sleeves
2 Coupling guard
1 Shaft end guard
1 Field regulator for D.C generators
1 Load resistance
1 Motor protection switch
3 Multimeter
1 Set of connection cables
Exercise
1. Connect the circuit diagram shown in fig 1.3a and 1.3b
2. Connect the 3 phase asynchronous motor
3. Couple the generator in fig. 1.1 to the 3 phase asynchronous motor
connected in step 2
4. Set the control unit as follows:
a) Speed
b) Torque
c) Operating mode
n
M
n
= 3000 rpm
= 1Nm
= constant
Range on multimeters
a) Voltage
b) Armature current, IA
c) Exciter current, IE
= 300 V
=1A
= 0.3 A
Set the load resistance to 100% (1000Ω)
5. Operate the generator
6. Adjust the load resistance to produce the generated voltage given in Table
1.2 below commencing at 250V (or at the highest value of VG could be
obtained). Measure the armature current and enter the value into the table.
7. Calculate the delivered electrical power, Pout = IA x VG
7
VG (V)
250
225
200
175
150
125
100
75
50
25
0
IA (A)
Pout (W)
Table 1.2
8. From the measured and calculated values, draw the load characteristics
curve:
a) VG (V) vs IA (A)
b) Pout (W) vs IA (A)
Questions
1. Describe how the delivered power depends on the armature current
2. Explain the shape of the load characteristic curve
8