Exp. No : Date : 1. MAGNETIZATION CHARACTERISTICS OF A D.C. … · of a D.C Shunt generator and to...
Transcript of Exp. No : Date : 1. MAGNETIZATION CHARACTERISTICS OF A D.C. … · of a D.C Shunt generator and to...
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE1
Exp. No : Date :
1. MAGNETIZATION CHARACTERISTICS
OF A D.C. SHUNT GENERATOR
AIM: To determine experimentally the magnetization or open circuit characteristics
of a D.C Shunt generator and to determine the critical field resistance and critical speed.
APPARATUS:
S.No. Item Type Range Quantity
1 Ammeter (M.C) 0 – 2 A 1 No
2 Voltmeter (M.C) 0 – 300 Volts 1 No
3 Rheostat Wire
wound 370 ohms / 1.7 A 2 No
4 Tachometer Digital 0-3000 rpm 1 No
NAME PLATE DETAILS:
Motor Generator
Voltage
Current
Output
Speed
Voltage
Current
Output
Speed
Electrical Machines-I Laboratory, EEE
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Choose the proper ranges of meters after noting the name plate details of the
given machine and make the connections as per the circuit diagram.
2. Keep the motor field rheostat (Rfm) in the minimum position. The jockey [J]
of the potential divider should be at the minimum voltage position [P] and start
the MG set.
3. Observe the speed of the generator using a tachometer and adjust to the rated
value by varying the motor field rheostat. Keep the same speed through out the
experiment.
4. Note down the terminal voltage of the generator. This is the e.m.f. due to
residual magnetism.
5. Increase the generator field current If (ammeter) by gradually moving the jockey
J in the direction P to Q. For every value of I0, note down the corresponding
voltmeter reading. Increase the field current till induced e.m.f is about 120% of
rated value.
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6. Repeat the same procedure for decreasing values of field currents (Ifg) and
finally note down the emf generated due to residual magnetism.
7. Draw the characteristics of generated emf (Efg) versus field current for both
increasing and decreasing values of field current. Draw the average O.C.C
8. Draw a tangent to the initial portion of average O.C.C from the origin. The slope
of this straight line gives the critical field resistance.
TABULAR COLUMN:
S.No.
ASCENDING DESCENDING
Field current (amp)
Generated voltage (volts)
Field current (amp)
Generated voltage (volts)
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
MODEL GRAGH:
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE4
PRECAUTIONS:
1. The experiment should be done at constant speed.
2. The jockey should be moved only in one direction (i.e., from P to Q or Q to P). It
should not be moved back and forth for obtaining a particular field current.
3. At zero field there would be some emf due to residual magnetism
4. Avoid parallax errors and loose connections
RESULTS:
VIVA QUESTIONS:
1. Under what conditions does the DC shunt generator fail to self-excite?
2. Define critical field resistance?
3. OCC is also known as magnetization characteristic, why?
4. How do you get the maximum voltage to which the generator builds up from
OCC?
5. What does the flat portion of OCC indicate?
6. Why OCC does not start from origin?
7. Does the OCC change with speed?
8. Why is Rsh>> Ra in dc shunt machine?
9. How do you check the continuity of field winding and armature winding?
10. How do you make out that the generator is DC generator without observing
the name plate?
11. How do you create residual magnetism if it is wiped out?
12. Why does the OCC differ for decreasing and increasing values of field current?
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE5
Exp. No: Date:
2.LOAD TEST ON A D.C SHUNT GENERATOR
AIM: To conduct a load test on a D.C. shunt generator and to draw its external and
internal load characteristics.
APPARATUS:
S.No. Item Type Range Quantity
1. Ammeter (M.C) 0 – 20 A
0 – 2 A
1 No
1 No
2. Voltmeter (M.C) 0 – 300 Volts 1 No
3. Rheostats Wire
wound 0 – 370 ohms/1.7 A 2 No
4. Tachometer Digital 0 – 3000 rpm 1 No
NAME PLATE DETAILS:
Motor Generator
Voltage
Current
Output
Speed
Voltage
Current
Output
Speed
Electrical Machines-I Laboratory, EEE
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as shown in the circuit diagram.Keep the motor field
rheostat in the minimum position and the generator field rheostat in the
maximum position at starting.
2. Start the MG set and bring it to the rated speed of the generator by adjusting
the motor field rheostat. keep the speed constant at this value through out
the test as the emf generated depends on speed.
3. Adjust the terminal voltage to rated value by means of the generator field
rheostat. Keep therheostat in this position through out the experiment as
its variation changes the field circuit resistance and hence the generated emf.
4. Apply the load and note the values of the load current, IL; terminal voltage, V
and field current, If at different values of the load until full load current is
obtained. Calculate the armature current in each case: Ia = IL + If
5. Make the connections for the measurement of armature resistance. Note down
the voltage drop Va across the armature for different values of current I passing
through it . Armature resistance in each case is calculated.
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6. Ra = Va / I., Ra (Hot) = 1.25 Ra. Take the mean of the values which are close
together as the resistance of the armature, Ra
7. Calculate the generated e.m.f. E at each value of the load current. E= V+ IaRa
8. Draw external characteristic, V versus IL and internal characteristic, E versus IL.
TABULAR COLUMN:
S. No. IL IF Ia VT E
1.
2.
3.
MODEL GRAGH:
Electrical Machines-I Laboratory, EEE
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RESULTS:
VIVA QUESTIONS:
1. Why is the generated e.m.f. not constant even though the field circuit resistance
is kept unaltered?
2. Find out the voltage drop due to full load armature reaction.
3. Differentiate between D. C. Shunt Motor and D. C. shunt Generator?
4. State the conditions required to put the D.C shunt generator on load.
5. Why the terminal voltage decreases when load is increased on the generator?
6. How do you compensate for the armature reaction?
7. What happens if shunt field connections is reversed in the generator?
8. The E.M.F. induced in armature conductors of a D.C shut generator is A.C or D.C?
9. Specify the applications of D. C. shunt Generators.
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE9
Exp. No: Date:
3. LOAD TEST ON D.C. SERIES GENERATOR
AIM: To obtain the external and internal characteristics of a DC Series generator by
conducting load test.
APPARATUS:
S.No. Item Type Range Quantity
1 Ammeter (M.C) 0 – 20A 1 No
2 Voltmeter (M.C) 0 – 300 Volts 1 No
3 Rheostat Wire
wound 370 ohms / 1.7 A 1 No
4 Tachometer Digital 0-3000 rpm 1 No
NAME PLATE DETAILS:
Motor Generator
Voltage
Current
Output
Speed
Voltage
Current
Output
Speed
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE10
CIRCUIT DIAGRAM:
PROCEDURE:
1. Choose the proper ranges of meters after noting the name plate details of the
given machine and make the connections as per the circuit diagram.
2. Keeping the motor field resistance minimum and the generator open circuited,
give supply and start the motor-generator set.
3. Adjust the speed of the M. G. Set to the rated speed of the generator using the
field rheostat.(Rfm)
4. Note down the voltage due to residual magnetism on no load.
5. Apply the load in steps and for each load note down the current and voltage
until the load current reaches the full load current.
6. Measure the generator resistance Rg by drop method.
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7. Calculate the generated e.m.f. E at each load from the relation, E= V+ IRg.
8. Draw the external characteristic, VT vs. II and the internal characteristic, EG Vs
Ia on the same graph sheet.
TABULAR COLUMN:
S. No. IL VT EG
VT + IL (Ra + Rs)
1.
2.
3.
4.
5.
MODEL GRAGH:
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE12
RESULTS:
VIVA QUESTIONS:
1. What are the applications of D.C series generator?
2. In what way does the series generator differ fundamentally from shunt generator?
3. Why does a series generator have rising characteristics?
4. To conduct the test on a D.C. Series generator, can we use any other prime
mover other than D.C shunt motor?
5. Why D.C series motor should not start without any load?
6. State the applications of the series generator.
7. Why at light load rangers the voltage increases?
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE13
Exp. No: Date:
4. LOAD TEST ON A D.C. COMPOUND GENERATOR
AIM:To obtain internal and external characteristic of a D.C. compound generator by
conducting load test.
APPARATUS:
S.No. Item Type Range Quantity
1 Ammeter (M.C) 0 – 20A
0 – 2A
1 No.
1 No.
2 Voltmeter (M.C) 0 – 300 Volts 1 No.
3 Rheostat Wire wound 370 ohms / 1.7 A 2 No.
4 Tachometer Digital 0-3000 rpm 1 No.
NAME PLATE DETAILS:
Motor Generator
Voltage
Current
Output
Speed
Voltage
Current
Output
Speed
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as shown in the circuit diagram.
2. Keep the motor field Rheostat in minimum position (Resistance) and the
Generator field rheostat in maximum position at starting.
3. Start the MG set and bring it to the rated speed of the Generator by adjusting
the motor field rheostat. Keep the speed of the MG set at constant value
through out the experiment as the e.m.f. generated depends on speed.
4. Adjust the terminal voltage of the generator to rated value by means of the
generator field rheostat. Keep the rheostat in this position throughout the
experiment as its variation changes the field circuit current and hence the
generated e.m.f.
5. Put on the load and note down the values of load current Ig and terminal
voltage Vg at the generator side, for different values of load until full load
current.
6. Draw external characteristics Vg vs. Ig & Internal Characteristics E Vs I Where
E= V+ IaRa.
Electrical Machines-I Laboratory, EEE
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TABULAR COLUMN:
S. No. IL IF VT Eg = V + Ia Ra
1.
2.
3.
4.
5.
6.
7.
MODEL GRAGH:
RESULTS:
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VIVA QUESTIONS:
1. Explain the difference between cumulative and differential compound
generators?
2. A cumulative compound generator is generating full load, what will happen if its
series field winding gets short – circuited?
3. Where you can use D.C. Compound Generator?
4. What do you understand from load curves?
5. Which causes the drop between internal & external characteristics?
6. Comment on the shape of load current Vc speed curve of the differential
compounded generator.
7. How do you reverse the terminal voltage of an over compounded short shunt
generator without effecting the over compounding?
8. Mention the applications of differential compound generator.
9. Mention the applications of over compound generator.
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE17
Exp. No: Date:
5. HOPKINSON’S TESTON DC SHUNT MACHINES
AIM:To perform Hopkinson’s test on the given motor generator set and determine
the efficiency of bothmotor and generator.
APPARATUS REQUIRED:
S. No. Item Type Range Quantity
1 Ammeter (M.C) 0 – 20 A 2 No
2 Ammeter (M.C) 0 – 2 A 2 No
3 Voltmeter (M.C) 0 – 300 Volts 3 No
4 Rheostats W.W 0 – 360 ohms / 1.7A 2 No
5 Tachometer Digital 0-3000 rpm 1 No
NAME PLATE DETAILS:
Motor Generator
Voltage
Current
Output
Speed
Voltage
Current
Output
Speed
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as per the circuit diagram. Keep the motor field rheostat at
minimum and generator field rheostat at maximum resistance position and the
switch K is in open position.
2. Start the motor generator set slowly with motor starter and adjust the field
rheostat of motor such that the motor/ generator rotates the at rated speed.
3. Excite the generator by decreasing the generator field rheostat resistance until
the voltmeter across the switch reads zero, then close the switch K
4. Load the generator in steps by decreasing the field rheostat resistance of the
generator or by increasing the field rheostat resistance of the motor.
5. Take the readings of all the meters for each load and measure the speed in each
step.
6. Open the switch K and reduce the excitation of the generator by increasing the
field rheostat of the generator.
7. Switch off the supply to motor-generator switch.
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MODEL GRAPH:Plot the output versus efficiency curves for both the motor and
the generator as shown below.
CALCULATIONS:
I1 = line current of motor I2 = exciting current of motor
I3 = load current of generator. I4 = exciting current generator
Armature cu loss in generator Wag = ( I3 + I4)2 Rag
Armature cu loss in motor Wam = ( I1+ I3 - I2)2 Ram
Shunt cu loss in generator Wfg= VI4 , Shunt cu loss in motor Wfm = VI2
Total power drawn from supply = VI1 = Total cu loss and Stray losses
Total stray loss for the set Ws= VI1 – [Wag + Wam + Wfg + Wfm ]
Stray losses of each machine = WS / 2
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Efficiency of motor :
Motor input Power = V (l1 + l3)
Armature Cu loss in motor = ( I1+ I3 - I2)2 Ra
Output power = input power to Motor – (motor armature copper loss + Motor shunt
field loss + Stray loss)
= ]2
][()( 2
2
23131
WsVIRIIIIIV am
100% XpowerInput
powerOutputEfficiency
Efficiency of Generator:
Generator output power = VI3
Input Power = (Output power + Gen. armature copper loss + Generator Shunt field
loss + stray loss)
]2
)( 4
2
433
WsVIRIIIV ag
100% XpowerInput
powerOutputEfficiency
TABULAR COLUMN:
S.No. N V1 I1 I2 I3 I4
1.
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Motor
S.No
Input Current ( I1+ I3 -
I2)
Armature Cu loss ( I1+ I3 - I2)2 Ram
Field cu Loss VI2
Stray loss
Ws / 2
Output Power
Input power
% Efficien
cy
1.
Generator
S.No
Input Current ( I1+ I3 -
I2)
Armature Cu loss ( I1+ I3 - I2)2 Ram
Field cu Loss VI2
Stray loss
Ws / 2
Output Power
Input power
% Efficien
cy
1.
PRECAUTIONS:
1) Keep the rheostats in motor and generator field circuit at proper positions while
starting the motor.
2) Excessive care while closing the parallel switch K. The voltmeter must read
zero for K to be closed.
RESULT:
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VIVA QUESTIONS:
1. What are the advantages of the test?
2. Can this test be applied to compound machines? Explain
3. When two D.C. machine s are paralleled as is done in this test, which machine
acts as generator and which machine acts as motor?
4. What are the disadvantages of this test?
5. What are heat run tests?
6. Hopkinson’s test is a _____________ test.
7. Hopkinson’s test on D.C. Machines is conducted at _________________ load.
8. The armature voltage control of DC motor provides ________________drive
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE23
Exp. No: Date:
6.FIELD TEST ON TWO IDENTICAL SERIES MACHINES
AIM:
To conduct the field test on two identical series machines and to find the efficiency at full
load.
NAME PLATE DETAILS:
S.NO Characteristic D.C Motor D.C Generator
1 Voltage 220V 220V
2 Current 19 A 13.6A
3 Speed 1500 R.P.M 1500 R.P.M
4 Power 5HP 3 Kw
5 Type Series Series
6 Insulation Class B Class B
APPARATUS REQUIRED:
S.NO Description Type Range Quantity
1 Volt meter M.C 0-300v 3
2 Ammeter M.C 0-20A 2
3 Resistive load Carbon Type 230V/1A 2
4 Tachometer Digital 0-10000 R.P.M 1
5 Connecting wires ---- ------ As required
6 RPS Digital 0-30V/2A 1
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CIRCUIT DIAGRAM: FIELD TEST ON TWO IDENTICAL SERIES MACHINES
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THEORY:-
This test is applicable to two series motors. Series motors which are mainly used for
fraction work are easily available in pairs two machines are coupled mechanically. One machine
runs normally as a motor and drives generator whose output is wasted in a variable load R Iron
and friction losses of two machines are made equal
i) by joining the series field winding of the generator in the motor armature circuit so that both
machines are equally excited and
ii) By running them at equal speed. Load resistance R is varied till the motor current reaches its
full-load value indicated by ammeter A1. After this adjustment for full load current different
ammeter and voltmeter readings are noted.
Let V = supply voltage; I1 = motor current; V2 = terminal P.D of generator; I2 = load current
Intake of the whole set = VI1 ; output = V2 I2 total losses in the set, wt = VI1 – V2 I2
Armature and field cu losses wcu = (Ra + 2Rse) I12 + I2
2 Ra
Stray losses for the set = Wt - Wcu
Stray losses per machine Ws = Wt – Wcu/2
PROCEDURE:
1. Connect the circuit as per the circuit Diagram
2. Initially the machine is loaded with half load and the 3 –point starter must be at ‘OFF’
position
3. Excite the circuit to D.C 220V supply by closing DPST switch
4. Start the motor by moving the 3-point starter handled gradually from ‘OFF” to “ON” position
5. Load the machine to full load by observing the Ammeter on the load side and record the
Ammeter, Voltmeter readings
6. After recording values bring the machines to half load by opening the load resistance and then
switch of the machine by opening the DPST switch.
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TO FIND ARMATURE RESISTANCE(RA):
1. Connect the circuit as per the circuit Diagram
2. Keep the rheostat connected in circuit is in maximum position
3. Excite the armature by 30V by closing the DPST switch
4. By varying the rheostat,note down the Ammeter and voltmeter readings
5. The ratio of average voltmeter and ammeter readings gives the value of Ra
CIRCUIT DIGRAM:
Sl.No Voltage Current
ARMATURE RESISTANCE (Ra)=
CIRCUIT DIGRAM :
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Sl.No Voltage Current
SERIES FIELD RESISTANCE (RSE)=
TO FIND SERIES FIELD RESISTANCE(RSE):
1. Connect the circuit as per the circuit Diagram
2. Keep the rheostat connected in circuit is in maximum position
3. Excite the field by 30V by closing the DPST switch
4. By varying the rheostat, note down the Ammeter and voltmeter readings
5. The ratio of average voltmeter and ammeter readings gives the value of RSe
TABULAR COLUMN:
CALCULATIONS:
Power Input to whole set=
Power Output of whole set=
Total losses=Power Input-Power Power Output
Total Armature copper losses=
Total field copper losses=
SNO Ammeter
Reading
(Ia)Amps
Voltmeter reading Ammeter
reading
IIAmps
Voltmeter
reading
Vg Volts
Input
Power in
watts
Output
Power in
watts V1 Volts V2 Volts
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Stray losses for the set (Ws)=
Stray losses of each machine=(Ws)/2=
AS A MOTOR:
Motor Input=
Motor losses=
Motor output= Motor Input-Motor losses
% efficiency=(Motor output/Motor Input )*100
AS A GENERATOR:
Generator Output=
Generator losses=
Generator Input=Generator output Generator losses
% efficiency=(Generator output/generator Input )*100
MODEL GRAPHS:
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PRECAUTIONS:
1. Initially 3-point starter is kept in ‘OFF’ position
2. Starter handle is moved slowly
3. Motor Must be switched ‘off with load
RESULT:
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Exp. No: Date:
7. SWINBURNE’S TEST AND SPEED CONTROL OF
D.C.SHUNT MOTOR
AIM:To pre-determine the efficiency of a DC shunt machine when run both as
generator and motor.
APPARATUS:
S. No. Name of the
Equipment Range Type Quantity
1. Voltmeter 0-300 V M.C 01
2. Ammeter 0-20A M.C 01
0-2A M.C 01
3. Rheostat 0-370Ω
/1.7A Wire wound
01
4. Tachometer
0-3000 rpm
DIGITAL
01
NAME PLATE DETAILS:
Voltage Output
Current Speed
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Choose the proper ranges of meters after noting the name plate details of the
given machine and make the connections as per the circuit diagram.
2. Keep the motor field rheostat (Rfm) in the minimum position, Start the motor by
closing the switch and operating the starter slowly.
3. Run the motor at rated speed by adjusting the motor field rheostat.
4. Note down the voltage, no load current and field current.
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TABULAR COLUMN:
S. No. V ILo If
MODEL GRAPH:
CALCULATIONS FOR SWINBURNES TEST:
From the no load test results,
Supply voltage = VL Volts.
No load line current = ILo Amperes.
Field current= If Amperes.
Therefore No load Armature Current = Iao = IL-If Amperes.
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Resistance cold = Rm
Effective resistance Re = 1.25 x Rm ohms.
No load copper losses are =Iao 2 Re
No load power input=VLIL
Constant losses = (No load power input - No load copper losses). ------------ (1)
Efficiency as motor:
Efficiency=output/input = (input – total losses)/ input.
Where total losses = constant losses + variable losses.
Constant losses are known value from the equation (1)
Variable loss = Ia2 Re , where Ia = IL-If
Input = VL IL.. VL is rated voltage of the machine
Assume line currents (IL) as 2, 4,6,----20A and find corresponding efficiency
Efficiency as generator:
Efficiency=output/input = output / (output + total losses).
Where losses = constant losses + variable losses
Constant losses are same for both motor and Generator
Armature Current = Ia = IL + IF
Variable loss = Ia2 Re
Output power = VLIL.VL is rated voltage of the machine
Assume load currents (IL) as 2, 4,6,----20A and find corresponding efficiencies
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TABULAR COLUMN:
As a Motor: Rated voltage VL = Rated speed N =
PRECAUTIONS:
1) Run the motor at rated speed and rated voltage.
2) Avoid loose connections and parallax errors.
As a Generator: Rated voltage VL = Rated speed N =
S.
No.
IL
PO = VLIL
Out
power
Constant
losses
Wconst.
Copper
losses
Wcu = Ia2 Re
Total loss
= (Wcons. +
Wcu)
Input power =
(output power
+ losses)
100XP
P
I
O
1.
S.
No. IL
PI =
VLIL
INPUT
Power
Constant
losses
W const.
Copper
losses
Wcu = Ia2
Re
Total
losses =
(Wcons. +
Wcu)
Output
power =
(input
power –
losses)
100XP
P
I
O
1.
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RESULT:
VIVA QUESTIONS:
1. Will the values deduced from the Swinburne’s method exactly coincide with the
values realized by direct loading on the machine? Why?
2. Why are the constant losses calculated by this method less than the actual
losses?
3. Can we conduct Swinburne’s test on dc series motor?
4. What are the drawbacks of Swinburne’s test?
Electrical Machines-I Laboratory, EEE
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SPEED CONTROL OF A D.C.SHUNT MOTOR
AIM: To vary the speed of the given d. c. shunt motor by armature control & field
control methods and to pre-determine the efficiency of a D.C. Shunt Motor by
Swinburne’s method.
APPARATUS:
S.No. Item Type Range Quantity
1 Ammeter (M.C)
0 – 2 A
0- 20 A
1 No
1 No
2 Voltmeter (M.C) 0 – 300 Volts 1 No
3 Rheostat Wire wound 370 ohms / 1.7 A 2 No
4 Tachometer Digital 0-3000 rpm 1 No
NAME PLATE DETAILS:
Voltage
Current
Output
Speed
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Choose the proper ranges of meters after noting the name plate details of the
given machine and make the connections as per the circuit diagram.
2. Keep the motor field rheostat (Rfm) in the minimum position, Start the motor by
closing the switch and operating the starter slowly.
3. Run the motor at rated speed by adjusting the motor field rheostat.
4. Note down the voltage, no load current and field current.
Part-A: Armature control method
1. Choose the proper ranges of meters after noting the name plate details of the
given machine and make the connections as per the circuit diagram.
2. Keep the motor field rheostat (Rfm) in the minimum position and the armature
rheostat (Rfg) in the maximum position, start the MG set.
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3. We supply and accelerate the motor by cutting out the armature circuit
resistance (Ra) until rated voltage is applied to the armature.
4. Adjust the field rheostat (Rf ) to make the motor run at its rated speed(Ns)
whenrated voltage is applied to the armature. This field current corresponds to
normal excitation.
5. Keeping normal excitation, vary the armature voltage (Va) by varying the
armature circuit resistance and note down the speed of the motor (N) for
different voltages. Note down the field current also.
6. Tabulate these readings and plot the graph VaVs N.
Part-B: Field control method:
Apply rated voltage to the armature and vary the field current (If) by varying the
field rheostat. Note down the speeds (N) at different values of field current. TAKE
CARE THAT THE SPEED DOESN’T EXCEEED 2000 rpm. Note down the
armature voltage also.
Tabulate these readings and plot the N Vs Ifspeed on no load.
TABULAR COLUMN:
S. No. V ILo If
1.
MODEL GRAPH:
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE39
TABULAR COLUMN:
Armature Control Method:
S. No. Va (Volts) N (rpm) If
1.
Field Control Method:
S. No. Va (Volts) N (rpm) If
1.
RESULT:
VIVA QUESTIONS:
1. Explain why the graph of armature speed control of motor is linear?
2. What is the shape of the curve of field control of method motor speed? Explain
why it is so?
3. What are the disadvantages of using armature control of speed no load?
4. How do you change the direction of rotation of a D.C. motor?
5. What are the limitations of shunt field control?
6. Comment on the efficiency calculated by this method?
7. What is meant by speed control?
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE40
Exp. No: Date:
8. BRAKE TEST ON D.C COMPOUND MOTOR
AIM: To determine the efficiency of a compound motor by conducting brake test
on the machine.
APPARATUS REQUIRED:
S. No. Item Type Range Quantity
1 Ammeter (M.C) 0 – 20 A 1 No
2 Ammeter (M.C) 0 – 2 A 1 No
3 Voltmeter (M.C) 0 – 300 Volts 1 No
4 Rheostats W.W 370 ohms / 1.7A 1 No
5 Tachometer Digital 0-3000 rpm 1 No
NAME PLATE DETAILS:
Voltage
Current
Output
Speed
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as shown in the circuit diagram.
2. Keeping the field rheostat (Rf) at the minimum position, switch on the supply
and start the motor.
3. Adjust the speed of the motor on no load to its rated value by means of the
field rheostat. DO NOT DISTRUB THE POSITION OF THE RHEOSTAT
THROUGH OUT THE TEST.
4. Put on the load by tightening the screws of the spring balances. Note down
the spring tensions, the speed, the voltage and the currents at different loads
until full load current is obtained.
5. The load on the drum is removed and the motor is stopped.
6. The efficiency is calculated at different load conditions
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE42
TABULAR COLUMN:
S.No. IL (A)
If (A)
W1 (Kg)
W2 (Kg)
W = W1-W2
(Kg)
N (rpm)
T= Wrg (Nm)
P0 =
2NT/60
P1 = VLIL
1000 XP
P
i
1.
MODEL GRAPH:
RESULT:
VIVA QUESTIONS:
1. Why differentially compounded motors are not in common use?
2. Differentially compounded after reversal?
3. Mention the applications of the cumulative compounded motor?
4. Which type of D.C starter is used to start the compound motor?
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE43
Exp. No: Date:
9.BRAKE TEST ON A D.C. SHUNT MOTOR
AIM: To obtain the performance characteristics of a D.C. shunt motor by conducting
brake test.
APPARATUS:
S. No. Item Type Range Quantity
1 Ammeter (M.C) 0 – 15 A 1 No
2 Ammeter (M.C) 0 – 2 A 1 No
3 Voltmeter (M.C) 0 – 300 Volts 1 No
4 Rheostat 0 – 360 ohms / 1.7A 1 No
NAME PLATE DETAILS:
Motor
Voltage
Current
Output
Speed
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CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as shown in the circuit diagram.
2. Keeping the field rheostat (Rf) at the minimum position, switch on the supply
and start the motor.
3. Adjust the speed of the motor on no load to its rated value by means of the field
rheostat. DO NOT DISTRUB THE POSITION OF THE RHEOSTAT THROUGH
OUT THE TEST.
4. Apply the load by tightening the screws of the spring balances. Note down the
spring tensions, the speed, the voltage and the currents at different loads until
full load current obtained.
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE45
TABULAR COLUMN:
S.No. IL (A)
VL (V)
W1 (Kg)
W2 (Kg)
W = W1-W2
(Kg)
N (rpm)
T= Wrg (Nm)
P0 =
2NT/60
P1 = VLIL
1000 XP
P
i
1.
2.
3.
4.
5.
6.
7.
8.
MODEL GRAPH:
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE46
RESULTS:
VIVA QUESTIONS:
1. Why did you use a 3-point starter for starting a D.C shunt motor?
2. If starter is not available, how can you start a D.C motor?
3. What is the efficiency range of a D.C motor?
4. Where can you use the D.C shunt motor?
5. Why is it considered as a constant speed motor?
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE47
Exp. No: Date:
10. SEPARATION OF LOSSES IN A D.C. SHUNT MOTOR
AIM: To perform suitable tests on the given D.C. shunt machine and determine
from the experimentthe stray losses and separates these into friction,
hysterics and eddy current losses.
APPARATUS REQUIRED:
S.No. Apparatus Type Range Quantity
1. Ammeter MC 0-2A&0-5A 2 Nos.
2. Voltmeter MC 0-300V 1 No.
3. Rheostat 370 ohm 1.7A 1 No.
NAME PLATE DETAILS:
Voltage
Field Current
Local Current
Speed
Power
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE48
CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as per the circuit diagram as shown in Fig.
2. Start the motor slowly using starter keeping the field and armature
rheostatsinminimum and maximum position respectively.
3. Adjust the field current to the rated value at no- load
4. Reduce the armature circuit resistance in steps, increasing the speed.
5. Take the readings of voltmeter, ammeter and speed at constant field current.
6. Continue the experiment till maximum speed is obtained by cutting out the
completeresistance in armature circuit (Do not exceed rated speed)
7. Bring the armature rheostat back to full resistance (initial) position.
8. Repeat the experiment with a reduced field current. (75% rated excitation).
9. Stop the motor
10. Tabulate the readings.
Electrical Machines-I Laboratory, EEE
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TEST READINGS:
Field Current (lf1) Field Current (lf2)
S.No. N V lf la
MODEL GRAPH:
Plot W/N Versus N for both the field excitations:
From the graph find out
B1 + D = bc/ab
B + D = ef/de
Determine
A+C and A1 + C
Solve for A, A1, B, B1, C, D.
S.No. N V lf la
N
WS / N
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE50
TABULAR COLUMN:
IF1……………. A IF2…………… A
S.No. V-la
Ra=Eb W=Ea la
W N
S.No. V-la Ra=
Eb W=Ea la
W N
PRECAUTIONS:
1. Keep the field current constant during each part of the experiment.
2. Check the position of the rheostat positions before stating the motor.
RESULT:
At rated speed the various losses are results
Hysterisis loss = W
Eddy Current loss = W
Friction loss = W
Wind age loss = W
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE51
VIVA QUESTIONS:
1. How Hysterisis losses occur in a D.C. Machine?
2. Where are eddy current losses occurring in a D.C. Machine?
3. How are the magnetic losses minimized?
4. How is brush contact resistance loss taken into consideration in practice?
5. Give the expression for hysterisis loss.
6. What is the effect of armature reaction?
7. How do you minimize cross magnetizing effect of armature reaction.
8. Differentiate MNA & GNA
9. Which test gives us stray losses?
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE52
Exp. No: Date:
11.RETARDATION TEST ON D.C SHUNT MOTOR
AIM:
To carry out the retardation test in a d.c shunt motor to determine the friction, iron or core
losses of the motor and to determine the moment of inertia of the motor.
NAME PLATE DETAILS:
S.NO Characteristic D.C Motor
1 Voltage 220V
2 Current 19A
3 Speed 1500 R.P.M
4 Power 5 HP
5 Field current 0.6 A
APPARATUS REQUIRE:
S.NO Description Type Range Quantity
1 Volt meter M.C 0-300v 02
2 Ammeter M.C 0-2A 02
3 Tachometer Digital 0-10000 R.P.M 01
4 Rheostat Wire wound 300/2A 02
5 Connecting
Wires
---- ---- As required
6 D.P.S.T.Switch
--- ---- 01
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE53
CIRCUIT DIAGRAM:RETARDATION TEST ON D.C SHUNT MOTOR
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE54
THEORY:
When a machine is loaded, the load current establishes an m.m.f. which appreciably
changes the space distribution of air-gap flux density wave. This leads to an increase in the core
loss from no load to full load. This increment in core loss caused by distortion of the air-gap flux
plus the increment in I2 R loss due to non-uniform distribution of conductor current is called
Stray loss. in other words, stray load loss consists of two components, one originating in iron
parts and the other in the armature conductors. In iron parts, the stray load loss consists of (a).the
eddy current loss in the stator frame, end covers etc. Caused by the armature leakage flux under
load. (b). the increased teeth loss due to distribution of the flux density wave. In the conductors
the stray load loss is due to the circulating currents setup in the conductors by the alternating
leakage flux produced by the load current. These circulating, or eddy currents make the
conductor current distribution non-uniform and as a result effective resistance of conductor
increases. This gives rise to additional conductor loss, called stray load loss. In d.c. machines,
stray load loss also occurs in the coils under going commutation. This loss is usually taken as
proportional to square of the load current. Stray load loss cannot determined accurately. In d.c.
machines by convention, it is taken as 1% of the rated out put for rating above 150 k
PROCEDURE:-
1. All the connections are as per the circuit diagram.
2. Initially DPDT Switch is to be kept in such a position that the Armature is connected to
supply through the starter.
3. 220V, DC supply is given to the motor by closing DPST switch
4. Vary the field rheostat and armature rheostat until the motor reaches its rated speed and
take voltmeter and ammeter readings.
5. The D.P.D.T switch is OPEN from the Armature Winding then voltage decreases
gradually.
6. One voltage reading as reference note down the time taken to fall the voltage from
original value to V1 and note down time.
7. Switch ‘OFF’ the supply by using DPST switch.
Electrical Machines-I Laboratory, EEE
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8. Again DPSTSwitch is to be kept in such a position that the Armature is connected to
supply through the starter.
9. 220V, DC supply is given to the motor by closing DPST switch
10. Vary the field rheostat and armature rheostat until the motor reaches its rated speed and
take voltmeter and ammeter readings.
11. Thronging DPDT switch to load position and the measure Imax , Imin , Vmaxand Vmin.
12. Calculate stray losses.
OBSERVATIONS TABLE:-
Case-1:-For t1 armature off.
S.NO Armature Voltage Time
Case-2:- For t2Armature connected to load.
Time Voltage Current
Min Max Min Max
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ST. PETER’S ENGINEERING COLLEGE56
PRECAUTIONS:-
1. Polarity of the meters should be as shown in the circuit diagram.
2. If voltmeter gives negative reading then interchange the voltmeter terminals
connections of a voltmeter.
3. Wait a few seconds in each step of the starter until the motor speed stabilizes.
Direction of the rotation shall be as given on the generator
RESULT:
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE57
Exp. No: Date:
12.LOAD TEST ON A D.C SEPARATELY EXCITED GENERATOR
AIM: To conduct a load test on a D.C. separately excited generator and to draw it’s
external and internal load characteristics.
APPARATUS:
S.No. Item Type Range Quantity
1. Ammeter (M.C) 0 – 20 A
0 – 2 A
1 No
1 No
2. Voltmeter (M.C) 0 – 300 Volts 1 No
3. Rheostats Wire
wound 0 – 370 ohms/1.7 A 2 No
4. Tachometer Digital 0 – 3000 rpm 1 No
NAME PLATE DETAILS:
Motor Generator
Voltage
Current
Output
Speed
Voltage
Current
Output
Speed
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE58
CIRCUIT DIAGRAM:
PROCEDURE:
1. Make the connections as shown in the circuit diagram. Keep the motor field
rheostat in the minimum position and the generator field rheostat in the
maximum position at starting.
2. Start the MG set and bring it to the rated speed of the generator by adjusting
the motor field rheostat. keep the speed constant at this value throughout
the test as the emf generated depends on speed.
3. Adjust the terminal voltage to rated value by means of the generator field
rheostat. Keep therheostat in this position throughout the experiment as
its variation changes the field circuit resistance and hence the generated emf.
Electrical Machines-I Laboratory, EEE
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4. Apply the load and note the values of the load current, IL; terminal voltage, V
and field current, If at different values of the load until full load current is
obtained. Calculate the armature current in each case: Ia = IL + If
5. Make the connections for the measurement of armature resistance. Note down
the voltage drop Va across the armature for different values of current I passing
through it . Armature resistance in each case is calculated.
6. Ra = Va / I., Ra (Hot) = 1.25 Ra. Take the mean of the values which are close
together as the resistance of the armature, Ra
7. Calculate the generated e.m.f. E at each value of the load current. E= V+ IaRa
8. Draw external characteristic, V versus IL and internal characteristic, E versus IL.
TABULAR COLUMN:
S. No. IL IF Ia VT E
1.
2.
3.
MODEL GRAGH:
Electrical Machines-I Laboratory, EEE
ST. PETER’S ENGINEERING COLLEGE60
RESULTS:
VIVA QUESTIONS:
1. Why is the generated e.m.f. not constant even though the field circuit resistance
is kept unaltered?
2. Find out the voltage drop due to full load armature reaction.
3. Differentiate between D. C. Shunt Motor and D. C. shunt Generator?
4. State the conditions required to put the D.C shunt generator on load.
5. Why the terminal voltage decreases when load is increased on the generator?
6. How do you compensate for the armature reaction?
7. What happens if shunt field connections is reversed in the generator?
8. The E.M.F. induced in armature conductors of a D.C shut generator is A.C or D.C?
9. Specify the applications of D. C. shunt Generators.