Download Electrical Engineering and Control System Lab

JAYA ENGINEERING COLLEGE
Department of Electrical and Electronics Engineering
Lab Manual
Sub: Electrical Engineering and Control system
Lab (EE 1292)
Class : IV Semester Computer Science & Engg.
Prepared by: Mr.P.Musthafa, Lecturer/EEE
Electrical Engineering and Control System Lab
Name of the Experiments
1. Verification of Kirchoff’s laws
2. Study of RLC series and parallel circuits
3. Open circuit and load characteristics of self-excited DC generator
4. Load test on D.C. shunt motor
5. Speed control of D.C. shunt motor
6. Swinburne’s test
7. Load test on single phase transformer
8. Load test on three phase induction motor (Squirrel Cage)
9. Load test on single-phase induction motor
10. Transfer function of separately excited D.C. generator
11. Transfer function of armature controlled D.C. motor
12. Transfer function of field controlled D.C. motor
13. Transfer function of A.C. servo motor
14. Transfer function of Compensating network
VERIFICATION OF KIRCHOFF’S LAWS
Aim:
To verify Kirchoff’s Current law and Voltage law.
Apparatus required:
S.No Name of the apparatus
1.
Ammeter
Type
MC
Range
Quantity
0-30 mA
1
0-10 mA
2
2.
RPS
Variable
0-30 volt
1
3.
Resistors
Carbon
1kohms
3
4.
Voltmeter
MC
(0-10)V
3
Theory:
Kirchoff’s first law: The algebraic sum of currents flowing through any junction is zero at all instants of time.
Kirchoff’s voltage law: The algebraic sum of voltages around a closed loop is equal to zero at all instants of time.
Procedure:
To Verify KCL
1.)
2.)
3.)
4.)
Connections are given as per the circuit diagram.
The input voltage is set at 8 Volt.
The ammeter readings are noted and tabulated.
The above steps are repeated for 10V, 12V and 15V.
To Verify KVL
1.)
2.)
3.)
4.)
Connections are given as per the circuit diagram.
The input voltage is set at 8 Volt.
Using Digital Multimeter/Voltmeter, voltage across each resistor is measured and tabulated.
The above steps are repeated for 10V, 12V and 15V.
Tabulation
To verify KCL
S.No.
I
mA
Input
Voltage
I1
mA
I2
mA
I1 + I2
mA
V
Volt
1.)
2.)
3.)
4.)
To verify KVL
S.No.
Input
Voltage
Voltage across
Voltage across
Voltage across
R1
R2
R3
V1 + V2 + V 3
Volt
Volt
V1
Volt
1.)
2.)
3.)
4.)
Circuit Diagram for Kirchoff’s Laws:
Kirchoff’s Current Law
Kirchoff’s Voltage Law
V2
Volt
V3
Volt
Observations:
It can be observed that the current I is equal to ( I 1 + I2
)
Also it can be observed that the applied voltage V is equal to (V1 + V2+ V3 )
Note: The differences in the above is due to tolerances in the resistors, meter resistances etc.
Result:
Thus the Kirchoff’s laws have been verified.
STUDY OF RLC SERIES AND PARALLEL ELECTRICAL CIRCUITS
Aim:
To study about RLC series and Parallel circuits also series and parallel resonance in electrical circuits.
Apparatus required:
S.No
1.
2.
3.
4.
5.
Name of the apparatus
Ammeter
DRB
DCB
DIB
Function generator
Type
MI
Range
(0-50)mA
Quantity
1
Theory:
A circuit is said to be in resonance when applied voltage V and the resulting I are in phase. Thus the
resonance , equilalent complesx impedenace of circuit cosists of only resistance R since V and I are in phase the
power factor of a resonance circuit is unity .
Series resonance :
The RLC series circuit of figure das a complex impedance z = r+j (L-1/c) = R+jx . the circuit is in
resonance when x=0
i.e
L=1/c =  1/Lc = o
Then since  =2f resistance frequency is given by
fo =1/2Lc
Parallel resonance:
The parallel circuit consisting of trancher with single pure elements R, L, C is an ideal circuit. However R, L, C
is a circuit of interest in general subject of resonance. This ideal circuit can be compared to the series circuit
examined above and it can be that a duality can be estimated.
For calibration purpose in parallel resonance we equate the imaginary part of the admittance of the circuit to be
zero to obtain the condition for resonance.
For an ideal forllel circuit
fo =1/2Lc
Procedure:
Series Resonance
1.Connections are given as per the circuit diagram-I.
2.The input waveform is chosen as sinusoidal waveform and its Voltage is set at 10 volt.
3. The frequency of the waveform is varied in suitable steps and in each step the values of ammeter (I) and voltage
across DRB (V) are noted down.
4. As the frequency is increased, it will be observed that the current in the circuit and voltage
across the DRB increase gradually and reach maximum values at a particular frequency,
which is referred to as resonant frequency. Thereafter, the current in the circuit and also the
voltage across the DRB decrease as the frequency is increased.
Parallel Resonance
1. Connections are given as per the circuit diagram-II.
2. The input waveform is chosen as sinusoidal waveform and its Voltage is set at 10 volt.
3. The frequency of the waveform is varied in suitable steps and in each step the values of ammeter (I) and voltage
across DRB (V) are noted down.
4. As the frequency is increased, it will be observed that the current in the circuit and voltage across the DRB
decrease gradually and reach minimum values at a particular frequency which is referred to as resonant
frequency. Thereafter, the current in the circuit and also the voltage across the DRB increase as the frequency is
increased.
Tabulation:
Series Resonance:
S.No.
Frequency of the Input Voltage
Hz.
I
mA
Parallel Resonance:
S.No.
Frequency of the Input Voltage
Hz.
I
mA
Graphs:
Graphs are drawn with Current or Voltage along Y-axis and Frequency along the X-axis.
Circuit Diagram for Study of Series and Parallel Resonance:
Result:
Thus the resonance had been studied in series and parallel electrical circuits.
SWINBURNE’S TEST
Aim:
Estimate the total constant loss of a DC shunt machine by conducting no load test and hence to predetermine it’s
when running as a motor and as a generator
Apparatus required:
S.No.
1.
Particulars
Voltmeter
2.
Ammeter
Range
0-300V
0-20A
0-1A, 0-2A, 0-5A
3.
Rheostat
400 ohms, 2A
Type
MC
Qty
1
MC
-
each 1
2
Theory:
Precautions:
1. The field Rheostat is kept at minimum position
2. The armature circuit resistance is kept at maximum position initially & by starting the machine the rheostat Rg is
selected so that starting current
3. Fuse with current rating of 20% of full load current are selected.
Procedure:
1. Connections are made as per the circuit diagram
2. The field rheostat is kept at minimum position and the armature resistance is kept at maximum position.
3. Switch is closed and motor is started using starter.
4. The armature resistance is gradually decreased to bring the machine to rated voltage.
5. The field circuit resistance Rf is increased so the machine is brought to rated speed.
6. At rated voltage & speed the current drawn by the machine Io the field If & applied Vo are noted.
7. After taking the readings the resistance Rf & Rg are brought back to their initial values and the machine is switched
off.
8. The total constant losses are determined.
9. The efficiency of the machine is calculated when running as a motor & as a generator.
10. The output Vs  are drawn.
Measure of armature Resistance
1. Connections are made as per the circuit diagram
2. The motor is prevented from rotation by means of the break drum.
3. The rheostat is kept at maximum position & supply is given by closing DPST switch
4. The readings of ammeter & voltmeter are noted & Ra is found.
Formula Used
1. Determination of Constant Losses
No load power I/P
No load Copper loss
=
Vo Io
=
Ia2 Ra
Determination of  while running as motor
Power Input
= VL IL
Armature Copper loss = Ia2 Ro
Power Output
= VL IL – Losses
Total Losses
= wc + Ia2 Ro

= Output / Input X 100
Determination of  while running as generator
Power Output
= VL IL
Armature Current = Ia = IL + If
Armature Copper loss = Ia2 Ro
Power Input
= VL IL + Losses
Total Losses
= wc + Ia2 Ro

= Output / Input X 100
SWINBURNE’S TEST
Name Plate Details
Tabulation
Determination of  when running as Motor:
IL
Ia=IL-If
VL
I/P
(A)
(A)
(V)
(W)
Copper
losses
(W)
Total
losses
(W)
O/P

(W)
(%)
Determination of  when running as generator
IL
VL
Ia
O/P
(A)
(V)
(A)
(W)
Copper
losses
(W)
Total
losses
(W)
I/P

(W)
(%)
To Measure RA
S.No.
Voltage (A)
Current
(A)
Ra
()
Speed
(rpm)
No load
Voltage Vo
No load
Current
Io
Field
current
If
At No Load
Model Calculations:
Viva Questions
Swinburne’s Test
1. What is the difference between brake test and swinburne’s test?
2. Advantages of Swinburne’s test.
3. Why the generator efficiency is always greater than motor efficiency?
4. What is the other name for swinburne’s test?
Result
Thus the total constant losses of a DC shunt machine by conducting no load test are estimated & its
efficiency is predetermine while running as a generator and as a motor.
SPEED CONTROL OF DC SHUNT MOTOR
Aim
To draw the speed control characteristics of DC shunt motor by (i) Armature control method (ii) Field control
method.
Apparatus Required
S.No.
Equipment Used
Range
Type
Qty
Theory
Armature Control Method
This is used when speed of motor below the no load speed is required. As the supply voltage is normally
constant, inserting a variable resistance in series with the armature circuit varies the voltage across the armature. As the
control resistance is increased the Pd across the armature id decreased. So the armature speed also decreases. In this
method speed can be varied up to the rated speed. This method is very expensive because of power loss and not suitable
for rapidly changing loads.
Field Control Method
The speed of a DC motor is inversely proportional to the flux per pole, when the armature voltage is kept
constant. By increasing the flux, the speed can be decreased and vice versa. Changing the field current can change the
flux per pole of a DC motor. The field current can be changed with the help of the shunt field current is relatively small,
the shunt field rheostat has to carry only a small amount of current, therefore the power loss is less. By this method,
speed below the rated speed cannot be obtained. By combining the field control and armature control methods it is
possible to sped variations below or above normal speed.
Precautions
1.
2.
3.
4.
Check for the correct fuse ratings.
Ensure there are no loose connections.
Field rheostat should be kept in minimum position initially.
Armature resistance rheostat is kept initially at maximum position.
Procedure
1.
2.
3.
4.
5.
6.
7.
The connections are made as per the circuit diagram.
Field rheostat is initially kept in the minimum position and the armature rheostat is in the maximum position.
Supply is given to the motor by closing the DPST switch.
Motor is started using a three-point starter.
Adjust the armature rheostat to get rated voltage.
In actual case adjust to about 200v, beyond this speed will be more than 1500 rpm.
The field rheostat is adjusted to make the motor run at the rated speed.
Armature Control Method
1. By varying the field rheostat, set the value of field current to a particular value say If=0.45A.
2. Now, by varying the armature rheostat, for various values of armature voltages, find the values of speed and
armature current repeat this procedure for various values of field current say 0.4A, 0.35A
3. Bring back the armature rheostat and field rheostat to initial position.
Field Control Method
1. By varying the armature rheostat, set the value of armature voltage to a particular value say V=180V.
2. Now by varying the field rheostat set the value of armature voltage field currents from 0.5A to 0.3A and note
down the values of speed.
3. Repeat this procedure for various values of armature voltages say 160V, 140V. Bring back the armature rheostat
and field rheostat to the initial position.
4. Switch off the DPST switch.
Speed Control of DC Motors
Name Plate Details
Tabular Column
Armature Control Method
Field Current (If) = A
Field Current (If) = A
Field Current (If) = A
S.No.
Armature
Speed
Armature
Speed(N)
Armature
Speed(N)
Voltage
V
(N)
(Rpm)
Voltage
V
(Rpm)
Voltage
V
(Rpm)
Field Control Method
S.No.
Armature Voltage
V
V
Field
Speed
Current
(N)
(IA) AMPS (Rpm)
Measurement of Ra
Armature Voltage
V
V
Field
Speed(N)
Current(IA)
(Rpm)
Amps
Armature Voltage
V
V
Field
Speed(N)
Current(IA)
(Rpm)
AMPS
S.No Armature Voltage
(Va ) (Volts)
Armature Current
(Ia) (Amps)
Armature Resistance
(Ra) (Ohms)
Model Calculation
Viva Questions
1.
2.
3.
4.
What are factors considered for controlling the speed?
What are the methods for speed control of motors?
Why field control method is better than armature control method?
Give Advantages and disadvantages ward-leonard system?
Result
Thus the speed control characteristics of DC shunt motor by (i) Armature control method (ii) Field control
method are done.
OCC and Load Characteristics of a DC Shunt Generator
Aim:
To draw the OCC and load characteristics of Self Excited DC Shunt Generator
Apparatus Required:
S.No. Apparatus
Range
Type
Qty
Theory
Precautions
a. Check for Correct Fuse Ratings.
b. Avoid loose connections.
c. The generator field rheostat is kept in maximum position and motor field rheostat is minimum
position.
d. Speed should be maintained constant through out the experiment.
Procedure
To Draw OCC
1.
The connections are given as per the circuit diagram.
2.
Supply is given to Motor by enclosing DPSTS 1.
3.
Motor is started using Three point Starter.
4.
The field Rheostat of Motor is varied to make the motor run at rated speed of the generator.
5.
The Voltmeter and Ammeter readings are noted.
6.
The field rheostat of generator is varied gradually and the readings of ammeter and volt meter are
noted in steps.
7.
Bring the generator field rheostat and motor field rheostat to the original position and open the
DPSTS 1.
To Draw Load Characteristics
1. The connections are given as per the circuit diagram.
2. Supply is given to Motor by enclosing DPSTS 1.
3. Motor is started using Three point Starter.
4. The field Rheostat of Motor is varied to make the motor run at rated speed of
the generator.
5. By adjusting the field Rheostat of the generator, the generator Voltage is brought to the rated value.
6. Now the load side DPST2 is closed and load is applied gradually upto 1255 of rated load.
7. The speed is maintained constant at each load.
8. The Readings of Ammeter and Voltmeter are noted at each load.
9. Remove the load completely.
10. Open the load side DPST2.
11. Bring the field rheostat of generator and motor to its original position and open the DPST1.
Tabulation
To draw OCC
S.No.
Open Circuit Voltage
Field Current
(Volts) V0
(Amps) If
To Draw Load Characteristics
S.No.
Load
Current (Il)
Amps.
Terminal
Voltage
(V) Volts.
Field
Current (If)
Amps
Armature
Current (Ia)
Amps
Induced
Voltage
Eg=V+IaRa
To Find Ra
S.No.
Model Calculation
Viva Questions
Armature Voltage (Va)
Volts
Armature Current
(Ia) Amps
Armature Resistance
(Ra) Ohms
Result
Thus the OCC and load characteristics of DC shunt generator when it is self & separately excited are
determined.
LOAD TEST ON SINGLE PHASE TRANSFORMER
Aim:
To determine the efficiency & regulation of a single  transformer conducting load test.
Apparatus Required:
S.No.
Apparatus
1.
Voltmeter
2.
Ammeter
3.
Wattmeter
4.
5.
Range
(0-300)V (0-150)V
(0-10)A
3000V,10A
150V,29A
Variac
Single
phase (230/115)V
transformer
2KVA
Type
MI
MI
UPF
UPF
Qty
Each 1
Each 1
1
1
1
Precautions
1. The zero error in the meters is corrected.
2. The variac is kept at minimum voltage position initially & its output is made to zero after the
completion of the experiment.
3. While energizing & dancercising there should not be any load on the transformer.
Procedure
1. The circuit connections are given as per the circuit diagram
2. The variac is kept at minimum output voltage position.
3. Here the transformer is used in step down configuration. The supply is given to low voltage winding
and the load is connected to high voltage winding.
4. The DPSTs2 is kept open and the transformer primary is energised by closing switch S1the output of
variac is increased to rated voltage 115V.
5. The NL power input, primary voltage and the no load secondary voltage 0V2 are noted.
6. Then switch s2 is closed and the transformer is loaded in steps up to 120% of full load. In each step
the power input w1, primary voltage V1, secondary winding voltages are noted.
7. The primary voltage V1 is maintained constant through out the experiment.
8. The load is reduced in steps & switch S2 is opened. The supply is switched off by making the output
of variac to zero.
9. The efficiency & regulation are calculated.
Formula used
1.
2.
3.
4.
5.
6.
No load secondary voltage = 0V2
No load primary voltage = 0V1
Power input = W1watts
Power output = W2 watts
Efficiency = output / input X 100
Regulation = UP = 0V2 – V2 / V2 X 100
Down = 0V2 – V2 / 0V2 X 10
Model Calculation
Viva Questions
OCC and Load Characteristics of DC Shunt Generator
1. What do you mean by self-excitation?
2. List the conditions for voltage build up of a dc shunt generator?
3. Name the different losses taking place in a DC machine?
4. Define eddy current loss and hysteresis loss?
5. What is the function of brushes in dc generator?
6. Define critical speed and critical resistance?
7. State the principle of generator?
8. What are the types of DC Generators?
9. What are the parts of dc generator? Why carbon is used as a brush material in a dc machine?
10. Tell the function of commutator in DC generator?
11. Why the armature core is laminated in dc machine?
Result
The load test is conducted on the given single phase transformer and the following curves are drawn.
1. Output Vs Efficiency
2. IL Vs % Regulation
LOAD TEST ON THREE PHASE SLIP RING INDUCTION MOTOR
AIM
To obtain the performance characteristics of a three-phase slip ring induction motor by conducting a load test.
APPARATUS REQUIRED:
S. No.
1
2
3
Name of the
Equipment
Ammeter
Voltmeter
Wattmeter
Range
Type
0 –10 A
0 – 600 V
MI
MI
2
Eleme
nt
500 V, 10 A, UPF
Quantity
1
1
1
4
Tachometer
0 – 3000 RPM
1
Digital /
Analog
THEORY
In an induction motor, the torque is proportional to the product of flux per stator pole, the rotor
current and power factor of the rotor.
Torque, T  I2 cos2
Where,
I2 = rotor current at stand still
2= angle between rotor EMF and rotor current
The starting torque of the three phase induction motor, Ts  R2 / Z2 In the slip ring induction
motor, external resistance can be added to the rotor circuit at starting. Hence the power factor of the rotor
circuit is easily improved. Therefore the starting torque of such a motor is high. The external resistance,
however, increases the rotor impedance and so reduces the rotor current. The torque developed in the
rotor is dependent upon the rotor resistance. Inserting external resistance in series with each phase in a
slip ring induction motor we can increase the value of rotor resistance.
Load Test on Slip Ring Induction Motor
Name Plate Details
The maximum value of the torque, however, is independent of the resistance. The speed regulation
can be obtained by varying the rotor resistance. The condition for maximum starting torque is that the
rotor resistance equals rotor reactance.
The torque is given in terms of slip as follows: T  sR2 / (R2 + s X2). If the resistance and inductance of
a given rotor is kept constant, the magnitude of the torque depends solely upon the slip, for a constant
applied voltage and frequency. For low values of slip, the reactance is negligible compared with the
resistance and hence, the torque is almost proportional to the slip. For large values of slip, the reactance is
large compared with the resistance and hence, the torque is now approximately, inversely proportional to
the slip. The starting torque of a slip ring induction motor is more compared to squirrel cage induction
motor. Also higher running torque can be obtained by introducing extra resistance in the rotor circuit.
Therefore, wherever a high starting torque or running torque or both are required, slip ring induction
motor can be used.
PRECAUTIONS
1. While starting and stopping there should not be any load on the brake drum.
2. Pouring water, cools the brake drum.
PROCEDURE
1.
2.
3.
4.
5.
The connections are made as per the circuit diagram.
TPSTS is closed and the supply is given.
The no load readings of Ammeter, Voltmeter, Wattmeter and speed are noted.
The brake drum is loaded by tightening the belt in steps of 1Amps.
For each load, note the readings of Ammeter, Voltmeter, Wattmeter, Tachometer and spring balance are
noted.
6. The load is gradually removed and the TPSTS is opened.
FORMULAE USED
1.
2.
3.
4.
5.
6.
7.
Torque, T = (S1 ~ S2) R x 9.81 Nm
Input Power = W * mf
Output Power = 2NT / 60 Watts
Percentage Efficiency (%) = [Output Power / Input Power] x 100
Percentage Slip = % s = [( Ns – N ) / Ns] x 100
Power factor = W / 3 VL IL
Where,
S1 and S2 are spring balance readings
c = Circumference of the brake drum
t = thickness of the belt
TABULATION
Circumference of the brake drum
Radius of the brake drum ( r )
Thickness of the belt ( t )
= ___ m.
= ___ m.
= ___ m.
IL
VL
W
N Spring Balance
Amps Volts Watts rpm Readings
S1 Kg
Input Torque Output Power % %s
Power (T) in Power factor Effici Slip
Watt Nm
in Watt
ency
S2 Kg
Model Calculation
Viva Questions
1. Write the difference between squirrel cage IM and Slip ring IM?
2.
3.
4.
5.
6.
Why does the rotor rotate?
Define slip and give the expression for the slip?
What is the use of adding external resistance in rotor circuit?
What is the condition for maximum torque? Tell the type of starter used for slip ring IM?
Draw the slip- torque characteristics.
RESULT:
Thus the performance and load characteristics of a three phase slip ring induction motor are drawn.
LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR
AIM
To obtain the performance characteristics of a three phase squirrel cage induction motor by
conducting a load test.
APPARATUS REQUIRED
S. No.
1
2
3
4
Name of the
Equipment
Ammeter
Voltmeter
2 – Element Wattmeter
Tachometer
Range
0 –10 A
0 – 600 V
600 V, 10 A
0 – 3000 RPM
Type
MI
MI
UPF
Digital / Analog
THEORY
Quantit
y
1
1
1
1
In an induction motor, the torque is proportional to the product of flux per stator pole, the rotor current and
power factor of the rotor.
Torque, T  I2 cos 2
Where,
I2 = rotor current at stand still
2= angle between rotor EMF and rotor current
The starting torque of the three phase induction motor, Ts  R2 / Z2 The resistance of a squirrel cage rotor
is fixed and small as compared to its reactance. The reactance is very large at the start because at standstill,
the frequency of the rotor currents equals the supply frequency. Hence, the starting current of the rotor,
though very large in magnitude (It is roughly 1.5 times the full load current), lags E2 by a very large angle.
Therefore the starting torque of a squirrel cage induction motor is very small.
Load Test on Squirrel Cage Induction Motor
Name Plate Details
The condition for maximum starting torque is that the rotor resistance equals rotor reactance. The
torque is given is terms of slip as follows: T  sR2 / (R2 + s X2).
If the resistance and inductance of a given rotor is kept constant, the magnitude of the torque depends solely
upon the slip, for a constant applied voltage and frequency. For low values of slip, the reactance is
negligible compared with the resistance and hence, the torque is almost proportional to the slip. For large
values of slip, the reactance is large compared with the resistance and hence, the torque is now
approximately, inversely proportional to the slip. The starting torque of a squirrel cage induction motor is
very low. Therefore this motor can be used only for the works which need low starting torque such as
centrifugal pumps, fans, blowers, line shafting, lathe works, etc.
PRECAUTIONS
1. While starting and stopping there should not be any load on the brake drum.
2. The motor is started using a star – delta starter.
3. The starter handle is moved from ‘Off’ position to ‘Start’ position and after the motor picks up
speed the handle is quickly moved to ‘Delta’ position.
4. The brake drum is cooled by pouring water.
PROCEDURE
1. Connections are made as per the circuit diagram.
2. TPSTS is closed and the supply is given.
3. Starter handle is moved from ‘Off’ to ‘Star’ position and after the motor picks up speed, the handle
is moved from ‘Star’ to ‘Delta’ position.
4. The no load reading of all the meters are taken.
5. Apply the load by tightening the belt in steps of 1A. For each load, note the readings of Ammeter,
Voltmeter, Wattmeter, Tachometer and spring balance.
6. Apply load up to 120% of full load current.
7. Gradually remove the load by loosening the belt and open the TPSTS.
FORMULAE USED
1.
2.
3.
4.
5.
6.
7.
Torque, T = (S1 ~ S2) R x 9.81 Nm
Input Power = W * mf
Output Power = 2NT / 60 Watts
Percentage Efficiency (%) = [Output Power / Input Power] x 100
Percentage Slip = % s = [( Ns – N ) / Ns] x 100
Power factor = W / 3 VL IL
Where,
S1 and S2 are spring balance readings
c = Circumference of the brake drum
t = thickness of the belt
TABULATION
Circumference of the brake drum = ________ m.
Radius of the brake drum (r)
= _________ m.
Thickness of the belt (t)
= ________ m.
IL Amps
V
W
N
Volts Watts rpm
Spring Balance
Readings
S1 Kg
Input
Power
KW
Torque Output %
%s
(T) in Power Efficie Slip
Nm
in Watt ncy
S2 Kg
Model Calculation
Viva Questions
1.
2.
3.
4.
What are the types of ac motors? And Why Induction motor is named so?
Which is the most commonly used induction motor and why?
Tell the advantages and disadvantages of Induction motor.
How hysterisis loss and eddy current loss is minimized?
5. Why the rotor slots are skewed in induction motor?
6. Write the principle of operation of induction motor?
Result:
Thus the performance and load characteristics of a three phase squirrel cage induction motor are
drawn.
TRANSFER FUNCTION OF AC SERVOMOTOR
Aim
To study the characteristics and transfer function of ac servomotor.
Theory
An ac servomotor is basically a 2Φ induction motor. The rotor of the servomotor is built with high resistance so
that its A/R ratio is small so speed torque characteristics will be linear. The excitation voltage applied to stator windings
should have a phase difference of 90ْ
Working
The stator windings are excited by voltage of equal RMS magnitude and phase difference. This results in
exciting current and which causes rotating magnetic field of constant magnitude. Rotating magnetic field sweeps over the
flux. Hence voltage induces current in stator conductors and current creates rotor flux.
Working of ac servomotor in control system
Constant voltage source excites the reference winding. The frequency is in range of 50-1000 Hz.
W(s) / E(s) = Km/ S (Zm) s+1
Where Km is Motor gain constant
Zm is Motor time constant
Application:
Control winding is excited by the modulated control signal and the voltage is of variable magnitude and polarity.
For the production of rotating magnetic field the control phase voltage must be of same frequency as reference phase
voltage. Hence the control signal is modulated by carrier signal whose frequency is same as that of reference voltage and
then applied to the control voltage.
For modulation purpose ac supply itself is used as carrier signal.
Let ec is control signal
Ecm is modulated control signal
If ec is positive then ecm and ecar will be same in phase so ecm = /E+ec/wswct for ec co.
Transfer function of AC Servomotor:
W(s) / Ec(s) = K1 /Js + K2 + B = Km/1+STm
Km = K1 / K2 + B = motor gain constant
Tm = J/ K2 + B = time constant (or) motor time constant
Let ω angular displacement of motor
W = dө / dt = angular speed
T = torque developed by the load.
B = Frictional viscous coefficient of conductor
J = moment of inertia of load.
K1 = slope of speed torque characteristics
Tm = torque developed by the motor.
Tm = J d2ө/ dT2 + B dө/dt
Tm = K1 – K2 dө / dt
J d2ө/ dT2 + B dө/dt = K1 – K2 dө / dt
J s2 ө(s) + Bө(s) = K1 E e (s) - K2 ө(s)
ө(s)/ Ee(s)
=
K1/ JS2+Bs+K2
TF of ac servomotor = Km/1+S2m
Km = K1/ K1+ B
Zm = J / K2+ B
Calculation
Km = k1 / K2 + B = 16 / 0.026 + 0.01875
= 357.54
Zm = J / K2+ B
= 0.052 / 0.026 + 0.01875 = 1.162
TF = 357.54 / 1+1.162
Result:
Thus the characteristic of ac servomotor was studied and its transfer function
To find K1
Torque T = 9.81 * r * S Nm.
S = Load in Kg
r = radius of shaft in m = 0.068m
Load (Kg)
Control Voltage Vc (V)
To find K2
Torque T = 9.81 * r * S Nm.
S = Load in Kg
r = radius of shaft in m = 0.068m
Speed (rpm)
Load (Kg) Torque (Nm)
Torque (Nm)
Transfer function of separately excited DC Generator
Aim:
To determine the transfer function of separately excited dc generator.
Apparatus Required:
S.No.
Name of the
Apparatus
1
Rheostat
2
Voltmeter
3
Ammeter
Type
Range
Qty
Double
tubular
MC
MI
MC
MI
400Ω / 2A
2
(0-300)V
(0-300)V
(0-2) A
(0-1) A
1
1
1
1
Theory:
Transfer function of a linear variant system is defined to be the ratio of Laplace transform of the other input
variable under the assumption that all initial conditions are zero. A dc generator is commonly used in control system for
power amplifications.
The transfer function of a separately excited generator is given as
Transfer function G(s) = Kg / Rf + SLf
Kg ----- generator constant (V/A)
Rf ------- resistance of field winding
Lf ----- inductance of field winding
Procedure
Determination of Kg
1.
2.
3.
4.
5.
6.
7.
Connections are given as per the circuit diagram.
Close the DPST switch.
The field rheostat of the motor is to be adjusted to bring the motor to the rated speed 1500 rpm.
By varying the field rheostat of the generated voltage are noted down.
Repeat the above step for various positions of the field rheostat of the generator.
Plot the graph, between field rheostat i.e. field current and the generated voltage.
The slope of the graph is a constant Kg.
Determination of Lf
1. Connections are given as per the circuit diagram.
2. The DPST switch is closed.
3. Single phase variac is adjusted and the various values of field current and field voltage are noted down.
4. The field coil impedance is calculated by Zf = Vf / If
Formula used
To obtain the transfer function
Zf ---- field impedance in Ω
Rf ---- field resistance in Ω
Xf ---- field reactance in Ω
F ---- supply frequency in Hz
Xf2 = Zf 2- Rf2
Field inductance = Xf / 2Πf
To obtain the rettling time ts
Rettling time = time required to reach 98% of steady state value (o.98iss)
Calculation
Derivation of transfer function
Transfer function = L E (g)/ L E f
= if Rf + Lf dit/dt = Ef(t)
Taking Laplace transform,
If (s) Rf + Lf (s) If (s) = Ef (s)
Generator constant Kg = Eg / If ----- Eg = Kg If
Eg (s) = Kg If (s)
If (s) = Eg (s) / Kg
Eg (s) / Ef (s) = Kg / Rf + sLf
Kg = ∆ Eg / ∆ If
Xf = √ Zf 2- Rf2
Xf = 2ΠfLf
Lf = Xf / 2Πf
Substituting value of Kg, Rf , Lf in transfer function we have transfer function of separately excited dc generator
Eg (s) / Ef (s) = Kg / Rf + sLf
TF = Eg (s) / Ef (s) = Kg / Rf + sLf
From graph
Kg = 307.69
Rf = 208.42 Ω
Xf = √ Zf 2- Rf2
= √(4.01 * 10 3)2 – (208.42)2
Xf = 4004.58
Lf = Xf / 2Πf = 4004.58 / 2Π * 50 = 12.75
Eg (s) / Ef (s) = Kg / Rf + sLf = 307.69 / 208.42 + s 12.75
Result
Thus the transfer function of separately excited dc generator was determined
TF =307.69 / 208.42 + s 12.75
Circuit diagram
Name Plate Details
Voltage
Current
Speed
DC Motor
220V
19A
1500rpm
DC Generator
220V
13.6A
1500rpm
Type
Excitation
Voltage
Excitation
Current
Shunt
220V
Shunt
220V
0.8A
0.8A
Tabulation
OCC
S.No
1
2
3
4
5
6
7
8
9
10
11
Voltage (V)
V (v)
If (A)
Field Current (A)
To Find Rf
To Find Zf
RΩ
V (v)
If (A)
Zf * 10 3 (Ω)
Transfer function of Compensating Network
(Lag , Lead, Lag – Lead)
Aim
To study the response of the following compensating network and to plot the magnitude and gain response for a
given range of input frequencies
1. Lag Network
2. Lead Network
3. Lag – Lead Network
Apparatus Required
1.
2.
3.
4.
Resistor (1.2 , 1 , 38 ,15KΩ) each 1
Capacitor (0.1 , 0.047 , 0.055 µF) each 1
CRO
Function generator
Theory
The widely employed compensators are lag , lead , lag-lead compensators. These are two situations in which
compensation is required. The first case the system is absolutely unstable and the compensation is done to stabilize
current as well as to achieve a specified performance.
The second case the system is stable but the compensation is required to obtain the desired performance system
which all type or higher are absolutely unstable for such types lead compensation is suitable.
A lead compensate speeds up the transient response and increase the margin of stability of a system. It also helps to
increase the system error constant through to a limited extent.
A lag compensator compensates improve the steady state behaviour of a system with i.e. while nearly preserving its
transient response.
When both the transition and steady state response improvement is required a lag lead compensator is required.
Thus basically a lag lead compensator is connected in series.
Procedure
1. Connections are made as per the circuit diagram.
2. Constant voltage is applied.
3. The output voltage of the circuit is observed for various frequencies of input.
4. The same procedure is repeated for all types of compensator.
Result
Thus the transfer function of compensating networks are studied.
Lead Network
S.No
1
2
3
4
5
6
7
8
Input Voltage
E(volts)
Frequency (Hz)
Output Voltage
E0 (V)
Gain G (dB)
10V
S.No
1
2
3
4
5
6
Frequency (Hz)
Phase Angle
Lag Network
E (V)
10v
Frequency (Hz)
Output voltage Eo (v)
Gain G (dB)
Frequency (Hz)
Phase Angle
Transfer function of field controlled DC motor
Aim
To determine the transfer function of field controlled dc shunt motor.
Apparatus Required
S.No
1
2
3
4
5
6
7
8
9
Name of the
Equipment
Ammeter
Ammeter
Voltmeter
Voltmeter
Voltmeter
Rheostat
Auto
Transformer
Tachometer
Stop Clock
Type
Range
Quantity
MC
MI
MC
MI
MC
Tubular
Single Phase
0-2.5/5A
0-15A
0-30v
0-300v
0-300v
400Ω/2A
2
1
1
1
1
1
Analog
(0-5000)RPM
1
Theory
The speed of a dc motor is directly proportional to armature voltage and inversely proportional to flux. In field
controlled dc motor the armature voltage is kept constant and the speed is varied by varying the flux of the machine since
flux is directly proportional to field current, the flux is varied by varying filed current. The speed control system is an
electromechanical control system. The electrical system consists of armature and filed circuit but for analysis purpose,
only field circuit is considered, because a constant voltage excites the armature. The mechanical system consists of the
rotating part of the motor and the load connected to the shaft of the motor. The field controlled dc motor has an open loop
transfer function.
Determination of J and B
Precautions
1. The motor field rheostat should be kept in minimum position
2. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram.
2. The DPTP switch is connected to 1-1’.
3. The motor is started by using three point starter.
4. The field rheostat of the motor is adjusted to speed above the rated speed (N+N) where N is the rated speed
(i.e 1500rpm) and N is 200rpm (assumes)
5. DPDT is changed from 1-1’ position and the time taken for the speed to fall (N-N) i.e 1300rpm is noted as t1.
6. The motor field rheostat is brought to the minimum resistance position. The motor is switched off and again
started.
7. The electrical load is switched on in order to compensate the armature drop.
8. DPDT is connected to position 1-1’ once again and adjust the field rheostat of the motor to get a speed slightly
above (N+N) i.e 1800rpm.
9. DPDT is moved from position 1-1’ to 2-2’ and when the speed falls to (N+N) i.e 1700rpm, note down the
voltmeter ammeter readings as VI and II and the stop clock is started.
10. The time taken when the speed falls to (N-N) i.e 1300rpm is noted as t2 and note down the values of voltmeter
and ammeter reading as V2 & I2.
11. The field rheostat of the motor is brought to minimum resistance position.
12. DPST switch is opened.
Determination of Zf
Precautions
1. Single phase variac is kept in minimum position
2. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram
2. DPST switch is closed.
3. Single phase variac is adjusted and various values of the field current and field voltage are noted.
4. The field impedance is calculated using ohms law i.e Rf = Vf / If
Determination of Kf
Precautions
1. There should not be any load while starting and stopping.
2. Field rheostat should be in minimum position.
3. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram.
2. DPST switch is closed.
3. The motor is started by using three point starter and brought to rated speed by varying the field rheostat.
The motor has to be loaded in steps till the rated value and each load, the values of armature current, voltage, field
current and the spring balance readings are noted down.
Determination of Rf
Precautions
1. The rheostat should be kept in maximum position.
2. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram.
2. DPST switch is closed.
3. The rheostat is adjusted and various values of the field current and field voltage are noted.
4. The armature resistance is calculated using ohms law i.e Rf = Vf / If
Determination of Ra
Precautions
1. Armature rheostat should be kept in maximum position.
2. loose connections should be avoided.
Procedure
1 Connections are made as per the circuit diagram.
2. DPST switch is closed.
3. The rheostat is adjusted and various values of the armature current and armature
voltage are noted.
4. The armature resistance is calculated using ohms law i.e Ra = Va/ Ia
Formula
Torque = 9.81 * (S1~S2) * R
Where R = r+ t/2
Where r is the radius of the break drum and t is the thickness of the belt i.e C = 2Πr
Lf = √Zf2- Rf2/ 2Πf (H)
Pc = 0.5 * (V1I1 + V2I2 + I12Ra + I22Ra) (W)
J = pc * t1 * t2 / 2Π2 (N12 – N22) (t1 - t2) (kg m2 / rad)
Pstray - 2Π2 (N12 – N22) * J / t1 (W)
P1 = Pstray / Π2 (N12 + N22) (NM /rad / Sec)
Transfer Function G(s) = km / S(1+Tfs)
Where km = kt / B(Rt) and J / B (kg m / N – S) (Rad / A Sec –Ω)
Where Tf = Lf / Rf, Tm = J /B
And time constant Tf = Lf / Rf
Tabulation
To obtain Armature resistance Ra
S.No
Armature Current (A)
Armature Voltage (V)
Armature resistance Ra – V/I Ω
Field Voltage (V)
Field Impedances Zf – V/I Ω
To obtain Field Impedance Zf
S.No
Field Current (A)
Determination of Kt
S.No
Voltage
applied
Field
Current(A)
Armature
Current (A)
Spring balance
S1 (kg)
S2 (kg)
Torque, T
(N – m)
To obtain Field resistance Rf
S.No
Field Current (A)
Field Voltage (V)
Field resistance Rf – V/I Ω
Determination of J and B
Position of DPDT from 1-1’ to 0-0’
S.No
Range of speed (rpm)
Time taken for the speed to
fall from (N+N) to (N - N).
t1 seconds
1700 - 1300
Position o0f DPDT from 1-1’ to 2-2’
S.No
Range of speed
(rpm)
1.
2.
1300 – 1700
1700 – 1300
Note:
Km = motor gain constant = KLf / Rf . B
Tf = Field time constant = Lf / Rf
Tm = Mechanical time constant = J / B
Time taken for the speed to
fall from (N+N) to (N - N).
t1 seconds
t2 =
Voltmeter
reading (volts)
Ammeter reading
(amps)
V1 =
V2 =
I1
I2
Result:
Thus the transfer function of a field controlled dc shunt motor is found to be
Q(s) / Vf (s) =
km / S (1 + ST f) (1 + STm)
Transfer function of armature controlled DC Shunt motor
Aim
To determine the transfer function of field controlled dc shunt motor.
Apparatus Required
S.No
1
2
3
4
5
6
7
8
9
Theory
Name of the
Equipment
Ammeter
Ammeter
Voltmeter
Voltmeter
Voltmeter
Rheostat
Auto
Transformer
Tachometer
Stop Clock
Type
Range
Quantity
MC
MI
MC
MI
MC
Tubular
Single Phase
0-2.5/5A
0-15A
0-30v
0-300v
0-300v
400Ω/2A
2
1
1
1
1
1
Analog
(0-5000)RPM
1
Transfer function of a linear time invariant system is defined to be the ratio of the laplace transform of the output
variable to the laplace transform of input variable under the assumption that all initial conditions are zero. A dc generator
is commonly used in control systems for power amplification.
The transfer function of a armature controlled motor is given by comparison of armature controlled and filed
controlled dc motors.
The time constant of the armature controlled dc motor is generally small compared to the field controlled dc motor
and hence the time response of the former is usually faster.
In armature controlled operation field requires a constant voltage source where as the field control operation
requires constant current source.
Determination of J and B
Precautions
1.The motor field rheostat should be kept in minimum position
2. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram.
2. The DPTP switch is connected to 1-1’.
3. The motor is started by using three point starter.
4. The field rheostat of the motor is adjusted to speed above the rated speed (N+N) where N is the rated speed (i.e
1500rpm) and N is 200rpm (assumes)
5. DPDT is changed from 1-1’ position and the time taken for the speed to fall (N-N) i.e 1300rpm is noted as t1.
6. The motor field rheostat is brought to the minimum resistance position. The motor is switched off and again
started.
7. The electrical load is switched on in order to compensate the armature drop.
8. DPDT is connected to position 1-1’ once again and adjust the field rheostat of the motor to get a speed slightly
above (N+N) i.e 1800rpm.
9. DPDT is moved from position 1-1’ to 2-2’ and when the speed falls to (N+N) i.e 1700rpm, note down the
voltmeter ammeter readings as VI and II and the stop clock is started.
10. The time taken when the speed falls to (N-N) i.e 1300rpm is noted as t2 and note down the values of voltmeter
and ammeter reading as V2 & I2.
11. The field rheostat of the motor is brought to minimum resistance position.
12. DPST switch is opened.
Determination of Za
Precautions
1. Single phase variac is kept in minimum position
2. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram
2. DPST switch is closed.
3. Single phase variac is adjusted and various values of the Armature current and armature voltage are noted.
4. The armature coil impedance is calculated using ohms law i.e Za = Va / Ia
Determination of Ra
Precautions
1. Armature rheostat should be kept in maximum position.
2. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram.
2. DPST switch is closed.
3. The rheostat is adjusted and various values of the armature current and armature voltage are noted.
4. The armature resistance is calculated using ohms law i.e Ra = va / Ia
The motor has to be loaded in steps till the rated value and each load, the values of armature current, voltage, field
current and the spring balance readings are noted down.
Determination of Kb
Precautions
1. Armature rheostat should be kept in maximum position.
2. Field rheostat should be kept in minimum position.
3. Loose connections should be avoided.
Procedure
1. Connections are made as per the circuit diagram.
2. DPST switch is closed.
3. Motor is started by using 3 point starter.
4. By adjusting the field rheostat, the motor is brought to rated speed.
5. By adjusting the armature rheostat, various values 0f the armature current and armature voltage, field current
and speed are noted.
6. The field current is kept constant through out the experiment.
7. Back emf is calculated using Eb = V-IaRa
8. Graph is drawn between Eb and N and slope of the graph gives Kb.
Determination of KT
Precautions
1. There should be any load while starting and stopping
2. Field rheostat should be kept in minimum position.
3. loose connections should be avoided.
Procedure
1 Connections are made as per the circuit diagram.
2. DPST switch is closed.
3. The motor is started by using three point starter and brought to rated speed by
adjusting the field rheostat.
4. The motor has to be loaded in steps till the rated value and for each load, the values of
armature current voltage and the spring balance reading are noted down.
Formula
Torque = 9.81 * (S1~S2) * R
Where R = r+ t/2
Where r is the radius of the break drum and t is the thickness of the belt i.e C = 2Πr
Lfa= √Za2- Ra2/ 2Πf (H)
Pe = 0.5 * (V1I1 + V2I2 + I12Ra + I22Ra) (W)
J = pe * t1 * t2 / 2Π2 (N12 – N22) (t1 - t2) (kg m2 / rad)
Pstray - 2Π2 (N12 – N22) * J / t1 (W)
P1 = Pstray / Π2 (N12 + N22) (NM /rad / Sec)
Transfer Function G(s) = ө (s) / Va (s) = Kt / Ra B / S {(1+STa) (1+STm) + Kbkt / Rab}
Where Ta = La / Ra, Tm = J /B (kg – m/ N-S)
And Kt and Kb can be calculated from the graphs.
Tabulation
To obtain Armature resistance Ra
S.No
Armature Current (A)
Armature Voltage (V)
Armature resistance Ra – V/I Ω
To obtain Field Impedance Za
S.No
Armature Current (A)
Armature Voltage (V)
Armature Impedance Za = V/I Ω
Determination of Kt
S.No
Voltage
applied
Field
Current(A)
Armature
Current (A)
Spring balance
S1 (kg)
S2 (kg)
Torque, T
(N – m)
S.No
Range of speed (rpm)
Time taken for the speed to
fall from (N+N) to (N - N).
t1 seconds
Determination of Kb
S.No
Range of speed
(rpm)
1.
2.
1800 – 1700
1700 – 1300
Time taken for the speed to
fall from (N+N) to (N - N).
seconds
Voltmeter
reading (volts)
Ammeter reading
(amps)
V1 =
V2 =
I1
I2
Determination of J and B
Position of DPDT from 1-1’ to 0-0’
Position of DPDT from 1-1’ to 2-2’
S.No
Voltage
applied
Field
Current(A)
Armature
Current (A)
Back emf Eb= V
Eb=V-IaRa
Speed(rpm)
Result:
Thus the transfer function of a field controlled dc shunt motor is found .
LOAD TEST ON SINGLE PHASE INDUCTION MOTOR
Ex. No
Date
Aim
To determine the load characteristics of single phase capacitor start-capacitor run induction motor.
Apparatus Required
S.No
Name of the
Equipment
Type
Range
Quantity
1.
2.
3
Voltmeter
Ammeter
Wattmeter
MI
MI
I Element
4.
Tachometer
Analog / Digital
0-300V
0-10A
0-300V, 10A,
UPF
0-3000RPM
1
1
1
1
Precautions
1. Check for correct fuse ratings.
2. Loose connections should be avoided.
3. There should not be any load on the brake drum initially.
Procedure
Connections are made as per the circuit diagram. Supply is given to the motor by closing the DPST switch and
motor is started using auto transformer. The no load readings of ammeter, voltmeter, wattmeter and tachometer are noted.
The motor is loaded gradually and the readings of ammeter, voltmeter, wattmeter, spring – balance, tachometer are noted
and tabulated till the load current is 90% of its rated value. Then load on the motor is released and motor is switched off.
Formulae used
1.R = r+ (t/2) (m)
2. Torque (T) = 9.81 * (S1~S2) * R (Nm)
3. Output power = 2пNT / 60 (Watt)
4. Slip = (Ns – N ) / Ns * 100
5. Efficiency = (output power / Input power ) * 100 (%)
Tabulation
1. Circumference of the brake drum =
m
2. Radius of the brake drum (r)
3. Thickness of the belt (t)
S.No
Line
Voltage
(V) in
volt
Line
Current
(I) in
Amps
Input
power
in
watt
=
=
m
m
Spring
Balance
Readings in
kgf
S1 S2 S1~
S2
Torque Speed
(T) in
in
Nm
RPM
Slip Output Efficiency
(%) power (%)
in watt
Graphs
1. Lin
e
Cur
rent
(A
mp)
Vs
Out
put
pow
er
(wat
t)
2. Tor
que
(N
m)
Vs
Out
put
power (watt)
3. Efficiency (%) Vs Output power (watt)
4. Speed (rpm) Vs Output power (watt)
5. Torque (Nm) Vs Slip
Result
Thus the load test on single phase induction motor is conducted and the load characteristics were drawn.
LOAD TEST ON DC SERIES MOTOR
Ex. No
Date
AIM
To conduct load test on DC series motor and to draw the performance and load characteristics of it.
APPARATUS REQUIRED
S.No. Equipment Used
Range
Type
Qty
THEORY
PRECAUTIONS
 Ensure that some load is applied to the brake drum initially (S1=S2=5kg).
 Check the correct fuse ratings.
 Ensure that there are no loose connections.
 Under no circumstances, the motor should be unloaded fully during operation.
PROCEDURE






The connections are given as per the circuit diagram.
Ensure that some load is applied to the brake drum initially (S1=S2=5Kg).
Supply is given to the motor by closing the DPST Switch.
Motor is started using the two point starter.
The readings of ammeter, voltmeter, tachometer and spring balance are noted.
The load is then gradually increased in steps and the readings are noted up to 125%of rated
load.
 In actual case, take readings up to 8.5 A.
 Decrease the load on the brake drum (until S1=S2=5Kg).
 The motor is switched off using the DPST switch.
Name Plate Details
FORMULA USED
Radius R=R+T\2 in Metres.
Torque T=(S1 S2 )*R*9.81 NM
Input Power P = Vi Ii Watts
Output Power P = 2NT Watts
Percentage Efficiency
= (Output Power/ Input Power)*100
Model Calculation
Viva Questions
1.
2.
3.
4.
5.
6.
7.
State the principle of motor?
Define back emf and why it is called so? Give the expression.
What is the function of commutator in motor?
Why the series motors are used in locomotives?
Why series motors should not be started at no load?
Tell the special features of DC series motor
What are the applications of series motor?
Result
Thus the performance and load characteristics of a DC series motor are drawn.
LOAD TEST ON DC SHUNT MOTOR
Exp No:
Date :
AIM
To draw the various characteristics curves by conducting load test on a DC shunt motor.
APPARATUS REQUIRED
S.No. Equipment Used
Range
Theory
Precaution
 Ensure that there is no load on the brake drum initially.
Type
Qty
 Check for correct fuse rating.
 Ensure that there are no loose connections.
 Field rheostat should be kept in minimum position initially.
Procedure
 The connections are made as per the circuit diagram.
 Ensure that no load is applied to the brake drum and the field rheostat is kept in minimum
position initially.
 Supply is given to the motor by closing the DPST switch motor is started using a 3point
starter.
 The field rheostat is adjusted to make the motor run at the rated speed.
 At no load, the readings of ammeter, voltmeter, tachometer and spring balance readings are
noted.
 The load is then increased in steps and the readings are noted up to 125% of rated load.
Remove the load on the brake drum. Bring the field rheostat to original position
 Open the DPST switch.
 An ammeter can be put into the field circuit to note the value of field current.
FORMULA USED
Radius R=R+T\2 in Metres.
Torque T= (S1 S2)*R*9.81 NM
Input Power P = Vi Ii Watts
Output Power P = 2NT /60 Watts
Percentage Efficiency
= Output Power/ Input Power
Model Calculation
Viva Questions
1.What are the applications of shunt motor?
2.What is the other name for shunt motor? Why it is called so?
3.What is the necessity of starter? Tell the types of starters used for DC motor
4.Tell the protective devices used in three point starter.
5.What is the advantage of 4-point starter over 3 -point starter?
6.Give the voltage equation of motor?
Tabulation: (DC Shunt Motor)
Circumference of the brake drum:
Radius of the brake drum (r)
Thickness of the belt
S.No
Line
Voltage
(Volts)
Line
Current
(Amps)
:
:
Speed
(Rpm)
Spring Balance
Readings
S1-S2
S1
S2
Kg
(KG)
(KG)
Torque
(N-M)
Output
Power
(Watts)
Input
Power
(Watts)
Efficiency
%
Result
Thus the performance and load characteristics of a DC shunt motor are drawn.
LOAD TEST ON DC SHUNT MOTOR
TABULAR COLUMN: (DC Series Motor)
Circumference of the brake drum:
Radius of the brake drum (r)
Thickness of the belt
:
:
Tabulation
Circumference of the brake drum:
Radius of the brake drum (r)
Efficiency
%
Input
Power
(Watts)
S1-S2
Kg
Output
Power
(Watts)
Spring
Balance
Readings
S2
S1
(KG
(KG)
)
Torque
(N-M)
Speed
(rpm)
Armature
Current
(Amps)
S.No
Line
Voltage
(Volts)
Line
Current
(Amps)
IL
:
Field Current
(Amps)
Thickness of the belt
: