EM-I manual

7/30/2019 EM-I manual

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ELECTRICAL MACHINES LAB-1List of experiments

1. Magnetization characteristics of DC shunt generator.Determination of critical field response.

2. Brake test on DC shunt motor. Determination of performancecurves.

3. Load test on DC series generator. Determination of characteristics.

4. Load test on DC compound generator. Determination of characteristics.

5. Swinburns test and speed control of DC shunt motor. Pre-determination of efficiency.

6. Load test on DC shunt generator. Determination of characteristics.

7. Hopkinsons test on DC shunt machines.

8. Brake test on DC compound motor. Determination of performancecurves

9. Retardation test on DC shunt motor. Determination of losses atrated speed.

10. Separation of losses in DC shunt motor .


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ELECTRICAL MACHINES LAB-1

EXP-1. MAGNETIZATION CHARACTERISTICS OFDC SHUNT GENERATOR

AIM : To draw the magnetization characteristics or open circuit characteristics of a self excited DC shunt generator and to determine Critical resistance, critical speed.

NAME PLATE DETAILS:

1. voltage :2. current :3. H.P/KW rating:4. speed :

APPARATUS REQUIRED:

S.NO Name of theequipment

Range Type Quantity

CIRCUIT DIAGRAM :


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THEORY:

PRECAUTIONS:

1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.

PROCEDURE:

1. make the connection as per the circuit diagram2. Ensure minimum resistance (rheostat in min position) in the field circuit.3. Switch on the supply and run the generator with out load.4. Vary the field current in the steps using the field rheostat.

i) Increasing mode: increase the field current in steps and not down thevalues of Field current (I f ) and Generated e.m.f (E) at each step.

ii) Decreasing mode: Decrease se the field current in steps and not downthe values of Field current (I f ) and Generated e.m.f (E) at each step.

5. Plot the graph between the average value (increasing and decreasing) of Fieldcurrent (I f ) and Generated e.m.f (E)

6. Find the critical resistance and critical speed

OBSERVATIONS :

S.No Field current (I f )(amps)

Generated e.m.f (E)(Vots)

Increasing mode Decreasing mode Increasing mode Decreasing mode


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SAMPLE CALCULATIONS:

EXPECTED GRAPH:

Field current (I f ) Vs Generated e.m.f (E G)

RESULTS AND CONCLUSION:


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EXP. 2. BRAKE TEST ON DC SHUNT MOTOR.

AIM : To study the performance of DC shunt motor by conducting Brake test.

NAME PLATE DETAILS :1. voltage :2. current :3. H.P/KW rating:4. speed :

APPARATUS REQUIRED:

S.NO Name of theequipment Range Type Quantity

CIRCUIT DIAGRAM:


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THEORY:

PRECAUTIONS:

1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.5. Release the load on the motor before switch OFF the supply

PROCEDURE:

1. Make the connection as per the circuit diagram2. Ensure minimum resistance (rheostat in min position) in the field circuit.3. Switch on the supply and slowly push the starter till the end and run the motor

with out load.4. Adjust the speed of the motor to the rated value by adjusting field resistance .5. Take the Noload readings of ammeter, voltmeter and speed.6. Slowly increase the load on the brake pulley by tightening the wheels in steps. At

each step note down the ratings ammeter, voltmeter, spring balance readings andspeed.

7. Release the load on the pulley and switch OFF the supply

OBSERVATIONS :S.No S1

(kgs)S2(kgs)

Load(S1-S2)(kgs)

Speed(N)(rpm)

Voltage(V)(volts)

Current(I)(amps)

Torque(T)(N-M)

O/PPower (watts)

I/P power (watts)

Efficiency( )

Torque T = (S 1 S 2)*R*9.81 N-MMotor output = 2NT/60 watts.Motor input = VI watts.Efficiency = output/ input =2NT/60*VI


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GRAPHS:

1. Efficiency Vs output.2. Speed Vs output3. Torque Vs output

4. Load current Vs output5. speed Vs output



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EXP-3. LOAD TEST ON DC SERIES GENERATOR.

AIM : To perform the load test on DC series generator and to draw the internal andexternal characteristics.

NAME PLATE DETAILS:1. voltage :2. current :3. H.P/KW rating:4. speed :

APPARATUS REQUIRED:


CIRCUIT DIAGRAM:


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THEORY:

PRECAUTIONS:

1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the machine ON load.

PROCEDURE:

1. Make the connection as per the circuit diagram.2. The motor generator set is started and brought to rated speed my varying themotor field rheostat.

3. When it is running at rated speed the generated field is adjusted to get ratedvoltage on no load.

4. The generator field rheostat is not disturbed through out the experiment.5. Load is put in steps on the generator the speed is adjusted to rated value for each

load and the load current I L and terminal voltage V are noted.6. The step 5 is repeated till the generator is over loaded by about 25%.

OBSERVATIONS :

S.No Load current (I L)(amps)

Terminal voltage (V T)(volts)

EMF Generated (E g)(volts)

EMF Generated (E g)=V + I aR a (volts).



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GRAPHS:

1. Internal characteristics: E g Vs I L2. External characteristics: V T Vs I L



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EXP-4. LOAD TEST ON DC COMPOUND GENERATOR.

AIM : : To perform the load test on DC compound generator and draw the internal andexternal characteristics.


APPARATUS REQUIRED:


CIRCUIT DIAGRAM:


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THEORY:

PRECAUTIONS:

1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.

PROCEDURE:1. Make the connection as per the circuit diagram.2. The motor generator set is started and brought to rated speed my varying the

motor field rheostat.3. When it is running at rated speed the generated field is adjusted to get rated

voltage on no load.4. The generator field rheostat is not disturbed through out the experiment.5. Load is put in steps on the generator the speed is adjusted to rated value for each

load and the load current I L, shunt Field current I sh and terminal voltage V arenoted.

6. The step 5 is repeated till the generator is over loaded by about 25%.

OBSERVATIONS :

S.No Terminalvoltage (V T)(volts)

Load current (I L)(amps)

Shunt fieldcurrent (I sh)(amps)

Ia= I sh+ I L(amps)

E=V T+ I aR a(volts)



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GRAPHS:

1. Internal characteristics: E g Vs I L2. External characteristics: V T Vs I L

RESULTS AND CONCLUSION


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EXP-5(A). SWINBURNS TEST ON DC SHUNT MOTOR

AIM : To perform the Swinburns test on given DC shunt machine and predetermine itsefficiency at any desired load both as motor and as generator.

NAME PLATE DETAILS:


APPARATUS REQUIRED:

S.NO Name of theequipment

Range Type Quantity

CIRCUIT DIAGRAM:


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THEORY:

PRECAUTIONS:1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.

PROCEDURE:

1. make the connection as per the circuit diagram2. Ensure minimum resistance (rheostat in min position) in the field circuit.3. Switch on the supply and run the motor at rated speed by adjusting the field

rheostat.4. take the readings of Line current I L0, shunt Field current I sh and terminal voltage

VT

OBSERVATIONS :1. No load Line current I L0:2. shunt Field current I sh :3. Terminal voltage V T:

Running as a motorArmature current R a=Rated current I r =Armature current for motor I ao= I 0-I f Constant losses (Wco) =Field current (I f ) =Terminal voltage V=

S.No Fractionof load

Loadcurrent

IL=X* I r

Armaturecurrent

Ia= I L*I f

Armaturecu losses

Wcu=Ia2R a

Totallosses

WT= Wco+Wcu

Input power

Wi=VI L

Output power

Wo= Wi-Wt

Efficiency = Wo/

Wi

Amps Amps Watts Watts Watts Watts %1. 1/42. 1/23. 3/44. 1


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Running as a generator:Armature current R a=Rated current I r =Armature current for motor I ao= I 0+I f Constant losses (Wco) =

Field current (I f ) =Terminal voltage V=

S.No Fractionof load

LoadcurrentIL=X* I r

ArmaturecurrentIa= I L*i f

Armaturecu lossesWcu=Ia2R a

TotallossesWT= Wco+Wcu

Input power Wi=VI L

Output power Wo= Wi-Wt

Efficiency = Wo/Wi

Amps Amps Watts Watts Watts Watts %1. 1/42. 1/23. 3/44. 1


RESULTS AND CONCLUSION :


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EXP-5(B). SPEED CONTROL OF A DC SHUNT MOTOR AIM : To control the speed of the DC shunt motor by varying field current an armaturevoltage.

NAME PLATE DETAILS:


APPARATUS REQUIRED:

S.NO Name of the

equipment

Range Type Quantity

CIRCUIT DIAGRAM:


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THEORY:

PRECAUTIONS:1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.5.

PROCEDURE:

1. make the connection as per the circuit diagram2. Ensure minimum resistance (rheostat in min position) in the field circuit andmaximum resistance in armature circuit.

3. Switch on the supply and run the motor at rated speed by adjusting the fieldrheostat.

4. Vary the field regulator in steps and take the readings of shunt Field current I f andspeed for each step.

5. keep the field rheostat in minimum position again.6. Vary the armature regulator in steps and take the readings of armature voltage V

and speed for each step.7. plot the graphs

OBSERVATIONS :

Field current control method :S.No Field current I f

(amps)Speed N(rpm)

Armature voltage method:S.No armature voltage V

(volts)Speed N(rpm)


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GRAPH:

1. Armature voltage V Vs speed

2. Field current I f Vs speed



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EXP-6. LOAD TEST ON DC SHUNT GENERATOR

AIM : To perform the load test on DC compound generator and draw the internal andexternal characteristics


APPARATUS REQUIRED:S.NO Name of the

equipmentRange Type Quantity

CIRCUIT DIAGRAM:

THEORY:


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PROCEDURE:1. Make the connection as per the circuit diagram.2. The motor generator set is started and brought to rated speed my varying the

motor field rheostat.3. When it is running at rated speed the generated field is adjusted to get ratedvoltage on no load.

4. The generator field rheostat is not disturbed through out the experiment.5. Load is put in steps on the generator the speed is adjusted to rated value for each

load and the load current I L, shunt Field current I sh and terminal voltage V arenoted.

6. The step 5 is repeated till the generator is over loaded by about 25%.

OBSERVATIONS :

S.No Terminalvoltage (V T)(volts)

Load current (I L)(amps)

Shunt fieldcurrent (I sh)(amps)

Ia= I sh+ I L(amps)

E=V T+ I aR a(volts)



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GRAPHS:1. Internal characteristics: E g Vs I L

2. External characteristics: V T Vs I L



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EXP-7: HOPKINSONS TEST OR REGENERATIVESTEST (BACK TO BACK TEST)

AIM : To perform Hopkinsons test on DC shunt machines.




CIRCUIT DIAGRAM:


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THEORY:


PROCEDURE :1. make the connection as per the circuit diagram2. Ensure minimum resistance (rheostat in min position) in the field circuit.3. Switch on the supply and start the motor whereas the switch S of the other

machine is open.4. Adjust the speed of the motor to its rated value by the rheostat.5. Adjust the voltage of the generator by the field rheostst until the voltmeter V 1

reads zero, there by showing that its voltage is same, both in polarity andmagnitude as that of the main supply.

6. Close the switch S to run the machine in parallel.7. Note down the reading of I 1, I2, I3, I4, I5 and V8. Repeat the procedure for different generator armature currents.

OBSERVATIONS:SNo Voltage

(volts)I1(amps)

I2(amps)

I3(amps)

I4

(amps)I5(amps)

Motor input(watts)

Motor output(watts)

Motor efficiency%

generator input(watts)

generator output(watts)

Generator efficiency%

CALCULATIONS: I1=I2=I3=I4=

I5 =V=

Total losses:


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Armature copper losses in motor= I 22R a wattsShunt copper losses in motor=V I 3 wattsArmature copper losses in generator = I 42R a wattsShunt copper losses in generator = V I 5 wattsMotor drawn supply from the supply= V I 1 watts

Total stray losses= V I1-[I 22

Ra +I 42

R a] watts.Stray losses for each machine =W/2 watts.

Motor input:=Armature input + Shunt field input=V I 2 +V I 3.Motor losses: Armature copper losses +Shunt copper losses +Stray losses=I22R a+V I 3 +W/2 (watts).

Motor output:Motor input losses.

Motor efficiency: output/ input.Generator output: V (I 4-I5 ) watts

Generator losses: Armature copper losses +Shunt copper losses +Stray losses=I42R a + V I 5 +W/2 ( watts).

Generator input= output= losses.

Generator efficiency: output/ input.




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EXP-8. BRAKE TEST ON DC COMPOUND MOTOR.

AIM : To study the performance of DC compound motor by conducting Brake test.




CIRCUIT DIAGRAM:

THEORY:


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PRECAUTIONS:1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.5. Release the load on the motor before switch OFF the supply

PROCEDURE:1. make the connection as per the circuit diagram2. Ensure minimum resistance (rheostat in min position) in the field circuit.

3. Switch on the supply and slowly push the starter till the end and run the motor with out load.4. Adjust the speed of the motor to the rated value by adjusting field resistance .5. Take the Noload readings of ammeter, voltmeter and speed.6. Slowly increase the load on the brake pulley by tightening the wheels in steps. At

each step note down the ratings ammeter, voltmeter, spring balance readings andspeed.

7. Release the load on the pulley and switch OFF the supply

OBSERVATIONS :S.No S1

(kgs)S2(kgs)

Load(S1-S2)(kgs)

Speed(N)(rpm)

Voltage(V)(volts)

Current(I)(amps)

Torque(T)(N-M)

O/PPower (watts)

I/P power (watts)

Efficiency( )

Torque T = (S 1 S 2)*R*9.81 N-MMotor output = 2NT/60 watts.Motor input = VI watts.Efficiency = output/ input =2NT/60*VI



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GRAPHS:

1. Efficiency Vs output.2. Speed Vs output3. Torque Vs output4. Load current Vs output5. speed Vs output



EXP -9. RETARDATION TEST


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AIM : To conduct a Retardation test on DC shunt motor and to determine dn/dt anddetermination of losses at rated speed.

NAME PLATE DETAILS:




CIRCUIT DIAGRAM:

THEORY:

PRECAUTIONS:1. Wear the hand gloves.2. Avoid loose connections and hanging wires.


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3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.

PROCEDURE:5. make the connection as per the circuit diagram

6. Ensure minimum resistance (rheostat in min position) in the field circuit.7. Switch on the supply and run the motor at rated speed by adjusting field rheostat.8. Raise speed to 1700 rpm (above rated speed) by adjusting field rheostat.9. open the DPST switch and start stop watch at 1650 rpm find T 1 while coasting

down to 1500 rpm.10. repeat procedure 2 for different speeds starting from 1650.

OBSERVATIONS :

Sno N 1rpm

N2Rpm TSec Va Ia dn/dt


GRAPHS:


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EXP -10 : SEPARATION OF LOSSES

AIM : To Separation the losses in a DC shunt motor.

.




CIRCUIT DIAGRAM:


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THEORY:

RECAUTIONS:1. Wear the hand gloves.2. Avoid loose connections and hanging wires.3. Make sure the initial value of field resistance is minimum.4. Dont start the motor ON load.

PROCEDURE:

1. make the connection as per the circuit diagram2. Ensure minimum resistance (rheostat in min position) in the field circuit.3. Switch on the supply and run the motor at rated speed by adjusting field rheostat.4. Adjust I f to rated value at no load.5. Reduce the armature circuit resistance in steps, increasing the speed.6. Take the readings of voltmeter, ammeter and speed at constant field current.7. Continue the experiment till maximum speed is obtained by cutting out the

complete resistance in armature circuit (do not exceed rated speed).8. Bring the armature rheostat back to full resistance(initial position).9. repeat the experiment with a reduced field (75%) .

OBSERVATIONS :

At full exciatation:Sno N

RpmVVolts

If Amps

Ia

Amps

V-IaR a=E b

W s=E bIa W s/N

At excitation:Sno N

RpmVVolts

If Amps

Ia

Amps

V-IaR a=E b

W s=E bIa W s/N


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GRAPHS:

Plot W s/N vs field excitation

From graphOP=A+CPQ=tan 1=slope of line PQPQ= B+DIf motor runs at different excitation then

OR= A+C 1

RS=tan 2 = slope of line RSRS=B+D 1

C-C 1=OP-OR D-D 1=tan 1-tan 2 =

If B1 max and B2max are flux densities of two different excitations then

6.1

2

1

6.1

2

11 max

max

=

=

EB

EB

B

B

C

C

Where EB 1 and EB 2 are back emf developed in motor at two different excitations then

2

2

1

2

2

11 max

max

=

=

EB

EB

B

B

D

D

C-C 1=OP-OR D-D 1=tan 1-tan 2


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A=B=C=D=Hysterisis losses= AN

Eddy current losses=BN2

Friction losses= CNWindage losses= DN2Stray losses= (A=C)N+(B+D)N 2


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