Experiment No 1
Title: Transmission ratio of the Transformer Board
Experimental Purpose: Determine the transmission ratio of the transformer built-in in the
Transformer Board.
Necessary Equipment:



Transformer board
Connecting wires
Voltmeter
Experimental Setup:
Experimental Procedure:





First of all, I observed all the safety precautions.
Then, I set up the circuit as shown in fig.
After that, I measured voltages U1 and U2 and recorded them.
I repeated the measurements for circuit (b).
I then calculated the transmission ratio once from the measured values, and once from the
number of windings.
Table:
Circuit
𝑼𝟏 /𝑽
𝑼𝟐 /V
Transmission
ratio determined
from voltages
Transmission ratio
determined from
of No. of windings
a)
231.8V
266.1V
0.87
1.78
b)
231.7V
133.0V
1.74
1.74
Evaluation:
Q.1 What do you ascertain when you compare the transmission ratio calculated from the
voltages with the transmission ratio calculated from the number of windings?
Answer: After observing the turn ratio from both of the methods, it can easily be concluded that
both of their values are almost same, rather the values obtained from voltage ratio was more
precise.
Q.2 Why is the transmission ratio not exactly “1” in a transformer with equal primary and
Secondary voltage?
Answer: The turn ratio can possible to be “1” only and only if it is an ideal transformer but in
real life it doesn’t exist so that’s why it can’t be exactly “1”.
Experiment No 2
Title: Current and voltage ratios on load of transformer.
Experimental Purpose: Measure the load current IL and the secondary voltage U2 on different
types of loads (resistive load, inductive load and capacitive load).
Necessary Equipment:



Transformer board
Connecting wires
Voltmeter Experimental
Experimental Setup:
Primary Side:
Primary side remains same in all circuit connections. i.e., no load, resistive load, capacitive load,
inductive load etc. Its connections are as follows:
Secondary Side:
Experimental Procedure:




First of all, I observed all the safety precautions.
Then, I set up the circuit as shown in fig.
After that, I measured voltages IL and U2 and recorded them.
I repeated the measurements for
 Resistive Load
 Capacitive load
 Inductive load
 I recorded all the values in the observation.
Table:
Load
𝑼𝟐 /V
𝑰𝑳 /mA
(a)
266.0V
66.1 mA
(b)
246.8V
71.6 mA
(c)
255.7V
88.8 mA
(d)
267.0V
71.8 mA
Graph:
266.8
U/V
261.8
256.8
251.8
246.8
66.1
71.1
76.1
81.1
86.1
I / mA
Evaluation:
Q.1 How does the transformer behave on different loads?
Answer: If primary voltage is kept the same then for different types of loads, the value of current
varied. Such that; the value of current was 0 for no-load, for resistive load it was same as the
utilization of the load, for inductive it increased w.r.t resistive load and for capacitive load it was
a bit lower than that of resistive load.
Experiment No 3
Title: No load characteristics of transformer.
Experimental Purpose: Record the no-load characteristic I0 = f (U0) of the transformer in the
Transformer Board. A regulating transformer (0...230 V AC) is required as a voltage source in
this experiment.
Necessary Equipment:




Transformer board
Connecting wires
Voltmeter
Ammeter
Experimental Setup:
Experimental Procedure:






First of all, I observed all the safety precautions.
Then, I set up the circuit as shown in fig.
After that, I measured voltages and current.
Measure the no load current Io. Enter the values in the table.
Transfer the values from the table to the grid provided in figure.
Draw the no-load characteristics.
 I recorded all the values in the table.
Table:
𝑼𝒐 /V
0
25
50
75
100
140
160
180
200
𝑰𝑜 /mA
0
0.04
0.09
0.13
0.19
0.28
0.35
0.41
0.48
Graph:
0.48
0.42
I 0 / mA
0.36
0.3
0.24
0.18
0.12
0.06
0
0
20
40
60
80
100
120
140
160
180
200
U0 / V
Evaluation:
Q.1 Why is the current characteristics not a straight line?
Answer: It does not obey homogeneity and additive properties. A circuit is linear if and only if
its input and output can be related by a straight line passing through the origin otherwise, it is a
nonlinear system.
Experiment No 4
Title: No load losses of transformer.
Experimental Purpose: Determine the iron losses using the no-load experiment. The iron losses
can be determined directly because the resistive losses of the winding are negligibly small in noload. A power meter or Watt meter (e. g. hps type 8705) is required to measure the active power
P0.
Necessary Equipment:





Trainer board
Connecting wires
Voltmeter
Ammeter
Power meter
Experimental Setup:
Experimental Procedure:
 First of all, I observed all the safety precautions.
 Then, I set up the circuit as shown in fig.
 After that, I measured the iron losses using the no-load experiment.
 The iron losses can be determined directly.
Experiment No 5
Title: Short circuit experiment
Experimental Purpose: The copper losses of a transformer can be determined with the shortcircuit experiment. To do this the secondary winding is short-circuited and the voltage on the
primary winding increased from 0 V until the rated current flows on the secondary side. Due to
the very low voltage on the primary winding the iron losses can be neglected.
Necessary Equipment:





Transformer board
Connecting wires
Voltmeter
Ammeter
Power meter
Experimental Setup:
Experimental Procedure:
 First of all, I observed all the safety precautions.
 Then, I set up the circuit as shown in fig.
 After that, I measured the copper losses using the short-circuit experiment.
Experiment No 6
(A)
Title: Down transformation of voltages on no load.
Experimental Purpose: Set up an auto-transformer with the TRANSFORMER BOARD
and examine the voltage ratios on no-load.
Theory:
The auto-transformer is a special version of a transformer. It differs from the normal twowinding trans- former in that it only has one common winding with one tap. The winding is
divided into two parts, the parallel and the series winding. With an auto-transformer the voltages
can be transformed up or down depending on the wiring. With the auto-transformer the voltages
can be transformed down. To transform up the in- put voltage U1 must be applied at the parallel
winding and the output voltage U2 to the series winding. As a result, the output voltage U2 is
higher than the input voltage U1. Since the input winding is connected conductively with the
output winding (common winding), there is no electrical isolation from the feeding mains. Autotransformers may therefore not be used for generating safety extra-low voltages. The advantage
of the auto-transformer is in the saving on winding copper and core iron. Smaller autotransformers are often designed as regulating transformers with a toroidal core. The efficiency of
auto-transformers is up to 99.8 % providing the voltages at the output and input do not differ by
more than 10 %. The total possible power emission of an auto-transformer is known as the
throughline power SD. It is transferred partly by the current line of the input winding and the
magnetic flow of the iron core. The more the transmission ratio ü approaches the value „1“, the
smaller the power transmitted with induction at constant through line power (SD = U2 x I2). This
power is known as construction power SB. The size of an auto- transformer depends on this.
Experimental Setup:
Experimental Procedure:
 Set up the circuit shown in figure.
 Measure the input voltage U1 and the output voltage U2 of the auto-transformer.
 Then calculate the output voltage U2 with the number of windings N1= 1978 and N2 =
1462.
Result:
In this experiment I Set up an auto-transformer with the Transformer Board and examine the
voltage ratios on load.
By performing experiment, I got following measurements,
U1 = Input voltage = 220 V
U2 = Output Voltage = 95V
By calculation I get,
U2calculated =U1measured.N2/ (N1+N2) =220. 1462/ (1978+1462) = 93.5
Evaluation:
Q.1 What do you ascertain when you compare the transmission ratio calculated from the
voltages with the transmission ratio calculated from the number of windings?
Answer: Measured and calculated value of the output voltage U2 match very well. The
transformer basic equation can therefore be used for the auto-transformer as well.
A transformer turns ratio is the division of the number of turns in the primary winding by the
number of turns in the secondary winding by the equation
T_R=\frac{N_P} {N_S}
This ratio should also equal the voltage of the primary winding divided by the voltage of the
secondary winding, as given by Vp/Vs.
Q.2 Why is the transmission ratio not exactly „1“in a transformer with equal primary and
secondary voltage?
Answer: Yes, ratio of turns is the same as ratio of voltages of windings for an ideal transformer.
Real transformers do not have perfect coupling-they have leakage inductance which appears as a
series inductance in each winding that does not couple to other winding inductances. This
reduces the voltage a little from a secondary winding.
(B)
Title: Down transformation of voltages on load.
Experimental Purpose: Set up an auto-transformer with the Transformer Board and examine the
voltage ratios on load
Experimental Setup:
Experimental Procedure:
 Switch the board on and measure the mains voltage U1. Then switch the board back off.
 Set up the circuit shown in figure.
 Measure the output voltage U2 of the auto-transformer.
Result:
By this experiment I concluded that, the calculated and measured values of U2 is approximately
samehe transformer basic equation can therefore be used for the auto-transformer as well.
From this experiment I got following observations,
Main voltage = U1 = 218V
Output Voltage = U2 = 92.3V
Evaluation:
Q.1 How does the transformer behave on different loads?
Answer: A control transformer is designed to provide rated output voltage at full VA. As the
load decreases, the output voltage will go up. Conversely, increases in load will result in lower
output voltages.
Q.2 How does the transformer behave on different loads?
Answer: A control transformer is designed to provide rated output voltage at full VA. As the
load decreases, the output voltage will go up. Conversely, increases in load will result in lower
output voltages.
Experiment No 7
(A)
Title: Up transformation of voltages no-load
Experimental Purpose: Set up an auto-transformer with the Transformer Board and examine
the voltage ratios on no-load.
Necessary Equipment:



Transformer board
Connecting wires
Voltmeter
Experimental Setup:
Experimental Procedure:
 Set up the circuit shown in figure.
 Measure the input voltage U1 and the output voltage U2 of the auto-transformer.
 Then calculate the output voltage U2 with the numbers of windings N1 = 1978 and N2 =
1462.
Result:
By this experiment I concluded that the calculated and measured values of U2 is approximately
same. Real transformers don not have perfect couplinghe transformer basic equation can
therefore be used for the auto-transformer as well.
From this experiment I got following observations,
Main voltage = U1 = 223V
Output Voltage = U2 = 394V
Calculated value from numbers of turns
U2calculated =U1measured. (N1+N2)/N1 =220. (1978+1462)/1978 = 387.8V
Evaluation:
What do you determine when you compare the measured and calculated value of the
output voltage U2?
Answer: The output voltage equals the input voltage scaled by a ratio of resistors: the bottom
resistor divided by the sum of the resistors. Measurements is the actual figure of the given thing.
Whereas calculation is made by using the measured figures and putting that into formula. The
actual (measured) resistance will vary from the nominal value due to subtle mechanical and
chemical differences that occur during manufacturing.
(B)
Title: Up transformation of voltages on load
Experimental Purpose: Set up an auto-transformer with the TRANSFORMER BOARD and
examine the voltage ratios on load.
Necessary Equipment:




Transformer board
Connecting wires
Voltmeter
Ammeter
Experimental Setup:
Experimental Procedure:
 Switch the board on and measure the mains voltage U1. Then switch the board back off.
 Set up the circuit shown in figure. Due to the expected high output voltage U2 two lamps
must be connected in series as a load.
 Measure the output voltage U2 of the auto- transformer.
Result:
In this experiment I set up an auto-transformer with the transformer Board and examine the voltage
ratios on load.
From this experiment I got following observations,
Main voltage = U1 = 210V
Output Voltage = U2 = 360V
Evaluation:
Question 1: How strongly does the output voltage drop under load in comparison with noload? What are the reasons for the drop?
Answer: Under no load conditions, there is no current flowing through the circuit, but there exist
terminal voltages, which are equal to the rated voltage of the device. Voltage drops occur when
loads are increased because an increase in current occurs, which depletes source capacity. The
term "voltage drop" isn't a one-size-fits-all term, and unfortunately a lot of dickheads use the
term interchangeably without the proper accommodating clarification.
There are two common ways to view "voltage drop". 1- measuring potential difference across
individual loads. 2- measuring potential difference across the source.
Experiment No 8
Title: Commissioning of the three-phase induction motor
Experimental Purpose: Operate the three-phase induction motor with squirrel-cage rotor on no
load
Necessary Equipment:




Three-phase Induction Motor (Type 2707)
Brake Unit (Type 2719)
Control Unit (Type 2730)
Universal Power Supply (Type 2740)
Experimental Setup:
Experimental Procedure:
1. I pushed the experimental machine onto the Brake Unit and couple it to the braking
machine.
2. I set up the experiment as shown in Fig.
3. I connected the motor to the 400 V mains in delta circuit and switch on the Control Unit.
4. Then I switched on the Universal Power Supply: speed, torque and direction of rotation
are displayed.
5. I watched the direction-of-rotation display and no-load speed of motor.
Note: The motor should turn to the right. Exchange the mains leads if necessary. Switch off the
Universal Power Supply First.
Observation & Calculations:
Direction of rotation: Right.
No load speed N0 = 1470 rpm
Experiment No 9
Title: Operation of a three-phase induction motor in star and delta circuit
Experimental Purpose: Operate the three-phase induction motor first in star and then in delta
circuit. Determine the torque characteristics
Necessary Equipment:




Three-phase Induction Motor (Type 2707)
Brake Unit (Type 2719)
Control Unit (Type 2730)
Universal Power Supply (Type 2740)
Experimental Setup:
In star
In Delta
Experimental Procedure:
 I set up the experiment as shown in Fig
 I start up the system in star circuit. The motor should turn to the right.
 I recorded the characteristic points asked for in Table
 I switched off the Universal Power Supply first and then the Control Unit.
 Then I set up the experiment as shown in Fig
 I switch on the Control Unit. Start the braking machine and switch on the Universal
Power Supply.
 I recorded the characteristic points asked for in Table
 To finish the experiment first switch off the Universal Power Supply and then the Control
Unit.
 I draw the torque characteristics in graphs respectively.
Table:
For Star:
Characteristics
Points
Speed (n) rpm
Torque (M) Nm
No load speed
1470
0.25
Rated speed
1440
0.58
1st sub value
1410
0.88
Pull out torque
1370
1.23
2nd sub value
1340
1.48
3rd sub value
1270
1.82
Min speed
120
1.91
Graph:
1470
1425
n rpm
1380
1335
1290
1245
1200
0.25
0.58
0.91 M Nm
1.24
1.57
1.9
For Delta:
Characteristics
Points
No load speed
Speed (n) rpm
Torque (M) Nm
1480
0.23
Rated speed
1440
1.62
1st sub value
1390
2.99
Pull out torque
1350
3.74
2 sub value
1290
4.57
3rd sub value
1250
5.09
Min speed
510
5.75
nd
Graph:
1470
1310
n rpm
1150
990
830
670
510
0.23
1.33
2.43
3.53
4.63
5.73
M Nm
Evaluation:
Q.1 How does the torque behave in star and delta circuit?
Answer: Higher current means higher torque, and lower current means lower torque. Delta
connected motor will draw more line current, so the torque it produces will also be higher
compared to the Star connection of the same motor. During starting the motor windings are
connected in star configuration and this reduces the voltage across each winding. This also
reduces the torque by a factor of three.
Q.2 When is the star/delta-startup circuit used? Describe the function of the circuit.
Answer: This is the reduced voltage starting method. Voltage reduction during star-delta starting
is achieved by physically reconfiguring the motor windings as illustrated in the figure below.
During starting the motor windings are connected in star configuration and this reduces the
voltage across each winding 3. This also reduces the torque by a factor of three.
Q.3 The rating plate of a three-phase induction motor carries the specification A/Y
230/400V. How does this motor behave in delta circuit on the 400V three phase mains.
Answer: When we use 400v the ampere will be the 1.732 times more than the 400v ampere.
There will be a drop in efficiency as well as Break away starting torque will be less. The mean
operating temperature will increase by 3 to 5deg. This is done by star and delta winding
connection.
Experiment No 10
Title: Efficiency, current and power factor of a three-phase induction motor
Experimental Purpose: Objective is to determine the characteristics for efficiency, current and
power factor of a three-phase induction motor with squirrel-cage rotor.
Necessary Equipment:






Three-phase Induction Motor (Type 2707)
Brake Unit (Type 2719)
Control Unit (Type 2730)
Universal Power Supply (Type 2740)
Power Factor Meter (10 A)
2 Multimeters
Experimental Setup:
Experimental Procedure:
 I set the experiment as shown in Fig
 Note: The motor should be operated in delta circuit and turn to the right.
 I recorded the characteristic points and wrote them in Table
 I measured the current I, the voltage U and the power factor cosΦ.
 Then I switched off the Universal Power Supply first and then the Control Unit.
 I draw the characteristics for efficiency, current in graph
Calculation:
N
(rpm)
M
(Nm)
POut
(kW)
U (V)
I (A)
cos
Ф
PIn
(kW)
%ɳ
no-loadspeed
1480
0
0
392.7
0.92
0.5
0.312
0
ratedspeed
1470
0.88
0.135
393.3
6.02
0.5
2.04
6.6
1st sub-value
1400
2.76
0.404
393.8
6.10
0.5
2.08
19.4
pull-outtorque
1370
3.31
0.474
394
6.22
0.5
2.122
22.3
2nd sub-value
1270
4.52
0.60
392.5
6.49
0.5
2.20
27.7
3rd sub-value
510
6.09
0.325
393.4
6.44
0.5
2.50
18.8
min. speed
240
5.44
0.136
392
7.56
0.5
2.566
5.3
Characteristic points
at
Graph:
7.52
6.42
I/A
5.32
4.22
3.12
2.02
0.92
240
440
640
840
1040
1240
1440
1040
1240
1440
n / rpm
27
22.5
n%
18
13.5
9
4.5
0
240
440
640
840
n / rpm
Evaluation:
Q.1 What do you learn from the characteristics?
Answer: In this experiment when the load is increased on motor, the current is increased.