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



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.



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:



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?



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:


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



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.



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:



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.



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:


1 Ammeter (M.C) 0 – 20A 1 No


3 Rheostat Wire

wound 370 ohms / 1.7 A 1 No


NAME PLATE DETAILS:

Motor Generator

Voltage

Current

Output

Speed

Voltage

Current

Output

Speed



CIRCUIT DIAGRAM:

PROCEDURE:



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.



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:



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?



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:


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



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.



TABULAR COLUMN:

S. No. IL IF VT Eg = V + Ia Ra

1.

2.

3.

4.

5.

6.

7.

MODEL GRAGH:

RESULTS:



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.



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




4 Rheostats W.W 0 – 360 ohms / 1.7A 2 No


NAME PLATE DETAILS:

Motor Generator

Voltage

Current

Output

Speed

Voltage

Current

Output

Speed



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.



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



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.



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:



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



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



CIRCUIT DIAGRAM: FIELD TEST ON TWO IDENTICAL SERIES MACHINES



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.



TO FIND ARMATURE RESISTANCE(RA):


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 :



Sl.No Voltage Current

SERIES FIELD RESISTANCE (RSE)=

TO FIND SERIES FIELD RESISTANCE(RSE):


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



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:



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:



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



CIRCUIT DIAGRAM:

PROCEDURE:



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.



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.



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



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.



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?



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:


1 Ammeter (M.C)

0 – 2 A

0- 20 A

1 No

1 No


3 Rheostat Wire wound 370 ohms / 1.7 A 2 No


NAME PLATE DETAILS:

Voltage

Current

Output

Speed



CIRCUIT DIAGRAM:

PROCEDURE:



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



2. Keep the motor field rheostat (Rfm) in the minimum position and the armature

rheostat (Rfg) in the maximum position, start the MG set.



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:



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?



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:





4 Rheostats W.W 370 ohms / 1.7A 1 No


NAME PLATE DETAILS:

Voltage

Current

Output

Speed



CIRCUIT DIAGRAM:

PROCEDURE:


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



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?



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:





4 Rheostat 0 – 360 ohms / 1.7A 1 No

NAME PLATE DETAILS:

Motor

Voltage

Current

Output

Speed



CIRCUIT DIAGRAM:

PROCEDURE:


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.



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:



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?



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



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.



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



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



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?



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



CIRCUIT DIAGRAM:RETARDATION TEST ON D.C SHUNT MOTOR



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.



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



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:



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:


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



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.



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:



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.

exp. no : date : 1. magnetization characteristics of a d.c. … · of a d.c shunt generator and to...

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