53669836 brake-test-on-a-d

BRAKE TEST ON A D.C. SHUNT MOTOR

AIM: - To perform brake test on the given D.C. shunt motor and obtain the performance
characteristics of the motor from the test observation.

APPARATUS:

Note: Prepare a list of apparatus required based on the name plate details and circuit
diagram in the following format.

S.No. Apparatus Type Range Quantity
1. Ammeter MC (0-2)A 1 NO
2. Voltmeter MC 0-300V 1 NO
3. Rheostat WW 370Ω/2A 1 NO
4. tachometer Digital 0-1000rpm 1NO
.

NAME PLATE DETAILS:

MACHINE MOTOR

Power 5HP
Voltage 220V
Current 20A
Speed 1500rpm

PROCEDURE:

1. Connect the circuit diagram as shown in fig.
2. Keep the field regulator Rsh at minimum resistance value.
3. Check that the belt on the pulley is free so that there is no load on the pulley.
4. Start the motor slowly using the starter.
5. Adjust the field current so that the motor runs at its rated speed.
6. Apply load on the pulley gradually in steps, tightening the belt around it.
7. Take the readings of the ammeter and voltmeter connected to the motor and input the
two spring balance readings and the speed at every step.
8. Cool the pulley throughout the loading period by pouring water.
9. Continue the experiment till full load of the motor is reached.
10. Tabulate the observation.

TEST READINGS :

Radius of pulley R = ……..m

S.No. Voltmeter Ammeter SpringBalance Speed in
Reading “V” Reading “A” Readings RPM
S1 Kg S2kG (N)

TABULATE THE RESULTS:

S.No. Current Speed Input Output B.H.P Efficiency
I N VI(Watt 2IINT(Watts) Output X 100
s) 60 Input

CALCULATIONS:-

NOTE: Radius of Drum Pulley R

Calculate for every load condition:-

The torque T= 9.81 R ( S1 - S2) N-m

Power output = 2IINT/60 Watts

2IINT 1
B.H.P. = X
60 735.5

GRAPHS:
Plot the Graphs for BHP versus efficiency
Plot the Graphs for BHP versus Torque
Plot the Graphs for BHP versus current
Plot the Graphs for BHP versus speed
Note: All the graphs are shown in Fig,

PRECAUTIONS:

1. Cool the pulley while the experiment is performed.
2. While measuring the radius of the pulley effective radius must be considered.

RESULTS:

Draw the performance characteristics for the D.C. shunt motor on a graph sheet.

VIVA QUESTIONS:

1. What is the back emf of the motor?
2. Why the speed falls as load increases for a D.C. Shunt motor?
3. What are the applications of D.C. Shunt motor?
4. When is the efficiency of the motor maximum?
5. Define commutation.
6. How do you minimize reactance voltage for sparkles commutation?
7. What should be the position of rheostat in the field circuit while starting?
8. What is the nature of load connected across dc motor?
9. What will happen when dc shunt motor is started with load?
10. Give the expressions for various torques in dc motors.
11. What is the effect on speed if part of the field winding is shorted?

BRAKE TEST ON D.C. COMPOUND MOTOR.

AIM: To perform brake test on the given D.C. compound motor and determine the
performance characteristics of the motor.

APPARATUS : Prepare a list of apparatus based on name plate and circuit diagram in
the following format.

01 Ammeter MC 0-2A 1NO
1NO
02 Voltmeter MC 0-300V
03 Rheostat WW 370Ω/1.7A 1NO
0-20A 1NO
04 Ammeter MC

NAME PLATE DETAILS:

PROCEDURE:

1. Make the connections as shown in fig.5.
2. Keep the field rheostat in proper position.
3. Check that the belt is loose and the motor is not loaded.
4. Start the motor slowly with the starter.
5. Note the readings of the voltmeter and ammeter.
6. Load the motor in steps by tightening the rope around the brake drum and
note the readings of the spring Balance voltmeter, ammeter and measure the speed.
7. Continue the experiment till full load is reached.
8. Slowly reduce the load and stop the motor.
9. Tabulate the observations

TEST READINGS:

Radius of Pulley:……………….

S. No. S1 S2 V I N

CALCULATIONS TABLE:

S.No. V I N Input Output Efficiency

CALCULATIONS:

NOTE: Radius of Drum Pulley R.

Power input = VI watt
2IINT
Power out put = 9.81 x R x (S1 – S2) Watts
60

2IINT 9.81 x Rx (S1 – S2)
B.H.P. = X
(Metric) 60 735.5

Output (Watts)
Efficiency: X 100
Input (Watts)

GRAPH:

Plot the graphs for BHP versus Current I
Plot the graphs for BHP versus Speed N
Plot the graphs for BHP versus Torque T
Plot the graphs for BHP versus Efficiencyη .

NOTE: All the graphs are shown in Fig

PRECAUTIONS:

1. Keep the field rheostat in minimum resistance position while starting the motor.
2. Start the motor slowly using the starter.
3. While loading, cool the pulley by pouring cold water

RESULT:

Brake test on the given D.C. compound motor is performed and the performance
characteristics are plotted.

VIVA QUESTIONS:

1) Explain the difference between “long shunt” and “short Shunt” compounding?
2) What are the uses of different types of compound motors?
3) What is differential compounding? How is it different from cumulative
compounding?
4) How do you reverse the direction of motor?
5) Draw the speed – torque curve for differential. Compound motor
6) What is flat compounding?
7) In a dc M/C, windage losses vary with speed in the proportion of …..
8) Brake test on dc motors is usually restricted to ….HP motors
9) Why do we pour water in the brake draw during brake test? What is the effect on
speed of dc compound motor if the series field winding is shorted?
10) How do you minimize iron losses in a dc machine?

Field’s Test on dc series machine.
AIM: To Determine the efficiency of the two given dc series machines which are
mechanically coupled.

Apparatus:

Name Range Quantity
DC Voltmeter 0-300V 1 No.
DC Ammeter 0-20A 2 No.
Tachometer 0-2000 rpm 1 No

Name Plate Details:

Motor Generator

Power = 5.0 hp. Power = 3.0 kW
Speed = 1500 rpm. Speed = 1500rpm
Voltage = 230volts Voltage = 220 volts
Current = 20amps Current = 13.6 amps

Procedure
1. Note down the ratings of the DC Series motor and DC Series Generator.
2. Connect the circuit as shown in the circuit diagram.
3. Put a minimum load of 400 watt on the generator.
4. Switch on the DC supply and closed the DPST Switch and now vary the DC
Starter till it holds with current coil.
5. Now keep the input DC Voltage constant at 220 volt DC.
6. Now increase the load of the Generator up to the rated value of armature current
and take down the readings of all the meters connected in the circuit.
7. Reduce the loads one by one till the motor speed does not exceed 1800 rpm
8. Note down the readings on the instruments at different loads.
9. Gradually, reduce the armature voltage of the prime mover. Keep a minimum
load of 400 watt and then switch off the supply

TABULATIONS:

Observations :
Armature resistance of the motor Ral = 2.0 ohms.
Series field resistance of the motor Rsel = 0.8 ohms.
Armature resistance of the generator Ra2 = 2.0 ohms
Series field resistance of the generator R se2 = 0.8 ohms.

CALCULATIONS:

V1 =
I1 =
VL =
IL =
Power Input Pin = V1 I1
Power output P out = VL IL
Total losses in two machines PL = Pin – P out

Field copper losses in the motor =P1= I1 2 Rsel
Field copper losses in the generator = P2=I12 Rse2

Armature copper losses in the motor =P3= I12 x Ral
Armature copper losses in the generator = P4=IL2 x Ra2

Total cu losses in the field and armature of generator and motor is P cu
Pcu = P1+P2+P3+P4 watts
PL – Pcu
Stray losses in each machine Ws = =
2
Motor Efficiency Calculations:

Power input to the motor Pin = V1 I1 2 Rse2

Total losses in the motor W ml = I12 Rsel + I12 + Ws
Motor Output Pout= Pin – Wml

Pout
% Efficiency = x 100 = x 100
P in
Generator Efficiency Calculations:

Generator output Pout (g) = VL IL
Total losses in the Generator Wgl = Ws + Il 2 Rse2 + IL2 Ra2

Power input to the generator Pin = Pout (g) + Wgl
Pout
% Efficiency of the generator = x 100
Pin

HOPKINSON TEST

AIM: To perform Hopkinson test on the given motor generator set and determine the
efficiency of both motor and generator.

APPARATUS:

01 Ammeter
02 Voltmeter
03 Rheostat

NAME PLATE DETAILES:

PROCEDURE:

1. Make the connection as shown in fig
2. Keep the rheostat in motor field at minimum and generator field at maximum
resistance position And the switch K open.
3. Start the motor generator set slowly with motor starter and adjust the field to rated
value by field rheostat of the motor.
4. Excite the generator by decreasing the generator field rheostat resistance
5. If the voltmeter Vs reads zero then close the paralleling switch K
6. Load the generator in steps by decreasing the field rheostat resistance of the generator
or by increasing the field rheostat resistance of the motor.
7. Take the readings of all the meters for each load and measure the speed in each step.
8. Reduce the excitation of the generator by increasing the field rheostat of the generator
and open the Switch K.
9. Switch the supply to motor-generator switch.
10. Tabulate the observations.

TEST READINGS:

S.NO I1 I2 I3 I4 V VS VG N

S.No. Motor Motor Motor Generator Generator Generator
Input Output Efficiency Input Output Efficiency

MODEL CALCULATIONS:

Input power to motor = V l1 Watts = Total excitation and Stray losses
Generator set = Total excitation and stray losses
Vl 1
Stray losses of each machine = Watts.
Z
Efficiency of motor :
Motor input Power = V (l1 + l2)
Output power = input power-Motor armature copper loss – Motor shunt field loss- Stray
loss
Ws

= V (l1 + l2) – (l1 + l2-l 3)2 Ram – Vl3 - Watts
2
Output
% Efficiency = x 100
Input
Efficiency of generator
Generator output power = VI2 Watts
Input Power = Output + Gen. Armature copper loss + Generator Shunt field loss + stray
loss

Ws
= VI2 + (l2 + l4)2 Rag + Vl4 +
2

Output
% Efficiency = X 100

Input

8. GRAPHS: Plot the output versus efficiency curves for both the motor and the
generator as shown in the figure .

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: Hopkinson test on the given D.C. Machine is performed and the performance
characteristics are plotted.

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 D.C. motor provides …… drive.

MAGNETIZATION CHARACTERISTIC OF A D.C. SHUNT GENERATOR.

AIM: To determine experimentally the magnetization or open circuit characteristic of a
generator and determine the critical field resistance and critical speed

APPARATUS:
Prepare a List of the apparatus required based on the name plate ratings and Circuit

S. No. Apparatus Type Range Quantity
1. Rheostats
2. Voltmeters
3. Ammeters
4. Tachometers
5. Knife switch

NAME PLATE DETAILS:

Specifications Motor Generator
Rating
Field current
Load current
Voltage

PROCEDURE:

1. Connect the circuit as shown in the fig
2. Set the potential divider to zero output keeping motor field rheostat in minimum
resistance position
3. Switch on the supply and start the motor with the help of the starter. Adjust the speed
of the motor generator set to the rated speed of the generator by controlling the motor
field resistance the set speed is to be maintained constant throughout the experiment Note
down the voltmeter reading at zero field current (lf). Increase the field current lf
uniformly in steps, by changing the potential divider tapping, simultaneously note down
the field current (lf) and the terminal voltage (E) across the generator armature terminals.
4. Continue the experiment till saturation of the field is reached.
5. Continue the experiment for decreasing values of If in steps by decreasing the tapping
of potential divider.

TEST READINGS:

Increasing lf Decreasing If
S.No. lf E S.No. Lf E

Critical Field Resistance: It is that value of the field resistance at which the D.C. shunt
generator will fail to excite.

Critical Speed: It is that speed for which the given shunt field resistance becomes the
critical field resistance. Critical field resistance is obtained by plotting the OCC as in
fig.2 and determining the slope of the tangent to the linear position of the curve from the
origin. While drawing the tangent, the initial position of the O.C.C is neglected.

OX is the tangent
Critical Field resistance

Rc = BC
AB

OY is the shunt Field resistance line

The Critical speed Nc = YZ x Rated Speed.
XZ

Rated speed is the speed at which the OCC is obtained.

PRECAUTIONS:

1. Perform the experiment at constant speed.
2. Readings are to be taken for uniformly increasing and then uniformly decreasing field
current.
3. Check must be made for residual magnetism otherwise; the field terminals may be
required to be reversed.
RESULT:
Magnetization characteristics are observed.

VIVA QUESTIONS:

1. Why is the magnetization characteristic different for increasing and decreasing of
values of lf?
2. What is the purpose of starter for the motor?
3. Why is the speed maintained constant during the experiment?
4. Why is the motor field resistance kept to a minimum while starting the motor?
5. What is residual magnetism?
6. Define critical resistance.
7. Define critical speed.
8. How do you determine critical resistance with help of O.C.C.?
9. Explain magnetization curve.
10. How do you determine critical speed graphically?
11. Define coercive force
12 Explain hysteresis phenomenon.

SEPARATION OF LOSSES IN A D.C. SHUNT MACHINE

AIM: To perform suitable tests on the given D.C. shunt machine and determine from the
experiment the stray losses and separates these into friction, hysterics and eddy current
losses.

APPARATUS:
Prepare a list of apparatus based on name plate and circuit diagram in the following
format.

MC 0-300V 1NO
02 Voltmeter
04 tachometer digital 0-2000rpm 1NO

NAME PLATE DETAIS:

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 rheostats in
Minimum 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 complete
resistance 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) stop the
motor.

9) Stop the motor
10) Measure the armature resistance by voltmeter-ammeter method using the circuit
diagram as shown in Fig.
11). Tabulate the readings.
TEST READINGS :

Field Current (lf1) A

S.No. N V lf la

Field Current (lf2) A

S.No. N V lf la

CALCULATIONS:
IF1…………….A IF2……………………A

S.No. V-la Ra= W=Ea W S.No. V-la Ra= W=Ea la W
Eb la N Eb N

CIRCUIT DIAGRAM:

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.

RESULT : At rated speed the various losses are results
Hysteresis loss = ………………W
Eddy Current loss = ……………… W
Friction loss = …………………… W
Wind age loss = ……………….. W

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.

VIVA QUESTIONS:

1). How Hysteresis losses occur in a D.C. Machine?
2) Where are eddy current losses occurring in a D.C. Machines?
3) How are the magnetic losses minimized?
4) How is brush contact resistance loss taken into consideration in practice?
5) Give the expression for hysteresis 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?

SWINBURNE’S TEST

AIM: To perform Swinburne’s test on the given D.C. machine and predetermine it
efficiency at any desired load both as motor and as generator.

ARATUS REQUIRED: Prepare a list of apparatus based on name plate and circuit

S. No. Apparatus Type Range Quantity
02 Voltmeter MC 0-300V 1NO
05 Tachometer digital 0-10000rpm 1NO
NAME PLATE DETAILS:

Voltage :

Field Current:…………………

Load Current:……………………….

Speed:………………………

PROCEDURE:

1) Make the connections as in fig
2) Start the D.C. motor with the starter slowly and bring it to rated speed.
3) Take the no load readings of input current, armature current, field current and input
voltage.
4) Stop the machine.
5). Measure the armature resistance using circuit diagram as shown in Fig.
6). Measure the field resistance using the circuit diagram as shown in Fig .by replacing
the armature by shunt field winding

Tabular columns:

Measurement of Ra Measurement of Rsh

S.No. Va Ia Va S.No. Vsh Ish Vsh
Ra = Rsh =
La lsh

Average Ra (t1) = ……………….. Ω Average Rsh (t1) = ……………….Ω

S.NO V(volts) IL(AMPS) If(amps) N(rpm)

MODEL CALCULATIONS:

PRECAUTIONS:
1 Keep the field rheostat at the minimum resistance position and armature rheostat in
maximum resistance position while starting the motor.
2. The experiment is to be performed only at no-load.
3. After starting the motor the armature rheostat must be fully cut- off.
RESULT:
Efficiency at no load condition calculated and performance curves drawn.
VIVA QUESTIONS

1. What are the advantages of the Swinburne test?
2. Why Swinburne test cannot be performed on series machines? Explain.
3. How do you obtain accurate measurements in this experiment?
4. How do you reverse the direction of motor?
5. Draw the speed – torque for diff. Compound motor.
6. What is Flat Compounding?
7 Ia a dc m/c, winding losses varies with speed in the proportion of -----------
8. Brake test on D.C. Motors are usually restricted to ---------- HP motors.
9. Why do we pour water in the brake drum during brake test?
10. What is the effect on speed of d.c. compound for if the series field winding is
shorted.
11. How do you minimize iron losses in a dc machine?

SPEED CONTROL OF D.C. SHUNT MOTOR

AIM: To determine the speed characteristics of D.C shunt motor by (i) field control and
(ii) armature control:

APPARATUS REQUIRED:

Note: Prepare a list of apparatus required based on name plate ratings and circuit diagram
in the following Format.

01 Ammeter MC (0-2)A 1NO
02 Voltmeters MC (0-300)V 1NO
04 Tachometer Digital 0-10000rpm 1NO

NAME PLATE DETAILS:

Rating ……………………………………. Load Current ………………………..

Voltage ………………………………….. Speed ………………………………...

PROCEDURE:

1. Make connections as per the circuit diagram fig.
2. Keep the field rheostat in the minimum resistance position and the armature
resistance in the maximum resistance position.
3. Start the motor by closing the switch and operating the starter slowly.
4. For the field control method, adjust the rheostat R2 so the voltmeter reads about 200
volts.
5. Increase the field resistance in steps there by decreasing the field current. Note
down the values of lsh, the shunt field current and the speed. Take enough readings
(8 to 10) to obtain a good curve.
6. For armature control, keep the field rheostat at a selected field current value note
the rated field current?
7. Decrease the armature resistance from maximum position in steps
keeping the field current at the set value. Note down the speed for
each value of armature voltage.

CIRCUIT DIAGRAM :

TEST READINGS:

Field control (Va=……) Armature Control (lf=…………..)
S.NO. Ish N S.No. Va N

GRAPH:

Plot Ish Vs N and VA (armature voltage) α N graphs.

PRECAUTIONS:
1. Keep the armature and field rheostats at proper positions while starting the motor.
2. Maintain constant field current for armature control and constant armature voltage for
field control part of the experiment.
RESULT:

The variation of speed with armature voltage and field current in case of D.C. shunt
motor is studied.

VIVA QUESTIONS:

1. What will happen if the shunt field is open during running?
2. What is the purpose of No volt coil in a D.C. Motor?
3. How do you change the direction of rotation of a D.C. Shunt motor?
4. What are the methods of speed control in a dc shunt motor?
5. In which method of speed control, above the base speed can be achieved, why?
6. List the merits and demerits of armature voltage control method.
7. What is the necessity of starter?
8. What is the function of OLR coil in dc starter?
9. What is the advantage of 4- point starter over 3-point starter?
10. Which is the precise method of speed control of dc motors?

LOAD TEST ON D.C. SERIES GENERATOR

AIM: To perform load test on a D.C. series generator and to draw the internal and
external characteristics.
APPARATUS:
Note: Prepare a list of apparatus required based on name plate ratings and circuit diagram
in the following format.

S.No. APPARATUS TYPE RAANGE QUANTITY
1. Rheostats WW 370Ω/1.7A 1NO
0-300V 1NO
2. Voltmeters MC
3. Ammeters MC (0-20)A 1NO
4. Tachometers Digital 0-10000rpm 1NO

NAME PLATE DETAILS:

Parameter Motor Generator
Rating
Load current
Field current
Speed

PROCEDURE
1). Connect the circuit as shown in fig.
2) Keep the motor field rheostat in minimum resistance position and do not connect any
load on the generator
3) Switch on the supply and start the motor with the help of starter.
4). Adjust the speed by controlling the motor field resistance.
5) Now, switch ON the load and for different values of load, note the ammeter and
voltmeter readings.
6). after loading the generator up to the rated value gradually reduce the load in steps and
switch off the supply.

CIRCUIT DIAGRAM :-
STARTER
L A Z

+
- 0- 30A
Y YY + A -

220 v, A Load
Z Rheostat
D.C M A
supply +
G V
AA -
ZZ AA

--

Fig. 10.1 : Load test on d.c. Series generator

TEST READINGS :

S.NO IL(AMPS) V(VOLTS) Eg(VOLTS)

Model calculations:
V= Eg – la (Ra + Rse)
Where
V = Terminal voltage
Eg = Emf generated in the armature (Volts)
La = Armature current (A) = lse = lL
Ra = Armature resistance (Ω)
Rse = Series field resistance (Ω)

PRECAUTIONS:

1). Loose connections are to be avoided.
2). Remove the load gradually in steps and switch OFF the motor
RESULT:

Performance characteristics are observed.

VIVA QUESTIONS.

1) How the internal characteristics are derived from external characteristics?
2) What are reasons for the failure of a D.C. series generator to build up voltage?
3) What is meant by critical resistance of a D.C. series generator?
4) What is the necessity of starter in D.C. Motors?
5) What material used for brushes, why?
6) Why are external characteristic lies below the internal characteristic in D.C. Shunt
generators?
7) What is the critical load resistance?
8) How do you control the speed of D.C. Motor?

LOAD TEST ON D.C. SHUNT GENERATOR

AIM: To perform load test on D.C. Shunt Generator and determine there from the
internal and external characteristics of the generator.

APPARATUS: Prepare a list of apparatus based on name plate and circuit diagram in
the following format.
S.No. Apparatus Type Range Quality
01 Ammeters MC (0-2)A 1NO

02 Voltmeters MC 0-300V 1NO

03 Rheostats WW 370/1.7A 2NO

04 Tachometer Digital 0-10000rpm 1NO

NAME PLATE RATINGS:-
Motor Generator
Power 5HP Power 3KW
Voltage 220V Voltage 220V
Current 20A Current 13.6A
Speed 1500rpm Speed 1500rpm

PROCEDURE:

1) Make the connection as shown in the circuit diagram as shown in the fig Start the
motor with the help of the starter.
2) Adjust the field regulator of the motor so that the generator runs at its rated speed.
3) Adjust the generator field regulator so that rated voltage is obtained at its terminals.
4) Gradually apply the load in steps and note down the readings of the load as given
on the name plate of the generator. Keep the speed constant at its rated value by
adjusting motor field regulator throughout experiment.
5) Plot the external load characteristic from the observations.
6) Determine the armature resistance experimentally using the circuit diagram in fig.
7) Take at least 6 readings of voltmeter and armature by varying the load resistance
and determine the average value of the armature resistance.

OBSERVATION TABLE:
Speed ………R.P.M.
S. No. Load Current Terminal Voltage Field Current
IL V If

CALCULATIONS:

Average value of armature resistance Ra = ----------Ω

S.NO. l a = l L + LF E = V + La Ra

GRAPHS :

1). Plot the external or load characteristic from the table.1 (lL Vs V curve )
2) Plot the internal characteristic or total characteristic from Table No.2 (la Vs E Curve)

PRECAUTIONS:

1) While starting the motor, field regulator (rheostat) must be in minimum position
2) While loading the generator, at every step speed of the generator must be maintained.
At rated value by adjusting the motor field regulator.
3). Decrease the speed before removing the load after the experiment is completed at full
load.
4) Do not over load the generator
RESULTS:

Internal and external characteristics are plotted by conducting load test on the given D.C.
Shut generator.

VIVA QUESTIONS:

1) If the shunt generator fails to buildup what could be the reason for it. Explain how
this can be over come
2) What is meant by armature reaction?
3) Why are the characteristics of the shunt generator drooping?
4) DC Generators are normally designed for max efficiency around ….load
5) What will happen when R-C load is connected across armature?
6) For a properly designed dc generators the over all efficiency could be of the order of
-----%
7) Define commercial & electrical efficiencies for dc generators
8) Which losses in a dc generator vary significantly with the load current?
9) Draw the internal and external characteristics for a dc shunt generator.

CIRCUIT DIAGRAM:

LOAD TEST ON DC COMPOUND GENERATOR.

AIM: To conduct a load test on given DC compound generator and to plot the internal
and external characteristics of the generator.

APPARATUS REQUIRED:

S.No Apparatus Type Range Quantity
1NO
02 Voltmeter MC
0-300V

05 Tachometer digital 0-10000rpm 1NO

NAME PLATE DETAILS:

Parameter Motor Generator
Rating 5HP 3KW
voltage
220V 220V
Load current 20A 13.6A
Speed
1500RPM 1500RPM

PROCEDURE:

Connect the circuit as per the circuit diagram shown in fig
1. Keep the field regulator of the motor in the minimum resistance position and regulator
of the generator in the maximum resistance position.
2. Switch on the supply and start the motor with the help of its starter.
3. Adjust the field regulator of the motor such that it runs its rated speed given on the
name plate.
4. Adjust the armature regulator of the generator to build up its rated voltage given on its
name plates on no load.
5. Note down the no loads of ammeter and volt meter in tabular form.
6. Increase the load gradually in steps and tabulate the readings
7. Plot the external characteristics is load current Vs terminal voltage.
8 Connect the generator for differentially compounding, repeat the process and plot the
external characteristics.

CIRCUIT DIAGRAM:

OBSERVATIONS:
S.NO V(volts) IL(AMPS) If(AMPS) Ia=IL+If Eg=V+Ia(Ra+Rf)

GRAPHS:-
1). Plot the external or load characteristics from table 1. (IL Vs V curve)
2). Plot the internal characteristics or total characteristics from table 2. (lL Vs Eb curve )

PRECAUTIONS:
1).Loose connections must be avoided.
2) The generator must be seen at constant speed through out the experiment.
3) The position of the starter must be checked before giving supply
4) The resistance of the field regulator of the motor must be adjusted to minimum
resistance position at the time of switching on the supply.
5).the resistance of the field regulator of the generator must be adjusted maximum
resistance at the beginning.
RESULTS:
Internal and external characteristics are plotted by conducting load test on the given DC
compound generator.

VIVA QUESTIONS:-
1). How many field windings are there in a compound generator? What are they?

2). what does compounding mean?
3). Draw the external characteristics for a level compound generator
4). in a compound wound generator which of the two fields dominate
5) Discuss the performance of a DC compound generator using only one field winding
at a time.
6). what is meant by commutation?
7) What are the different methods oaf obtaining spark less or good commutation?
8) Why do you perform load test?
9) Differentiate cumulative & differential compound generators.
10). Give at least three applications of dc compound generators.
11) What is the critical resistance’s in a dc shunt machine?

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