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I. Objective

The students want to understand the principles of DC compound short

shunt generator operation. The student must be aware of the parameters used

to measure dc motor generator performance. In addition to, the student must

able to know the connection and characteristic of DC compound short shuntgenerator.

II. Equipment

Universal power supply

Dc Compound Wound Machine

Torque & Speed Control Panel

Dynamometer Machine

Switched Three Phase resistance Load

Shaft Coupling and Key

System Frame

Standard set of patch leads

Voltmeter and ammeter

III.Theory/ Background

There are three types of self-excited dc generators they are 1) Series 2) Shunt and 3)

Compound.

A series DC generator is in which the armature winding is connected in series with the

field winding so that the field current flows through the load as well as the field

winding.Field winding is a low resistance,thick wire of few turns. Series generators are also

rarely used!

A shunt DC generator is in in which the field winding is wired parallel to armature

winding so that the voltage across both are same. The field winding has high resistance andmore number of turns so that only a part of armature current passes through field winding

and the rest passes through load.

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A compound generator has two field findings namely Rsh and Rse. They are basically

shunt winding (Rsh) and series winding (Rse). Compound generator is of two types 1)

Short shunt and 2) Long shunt.

Short shunt:- Here the shunt field winding is wired parallel to armature and series

field winding is connected in series to the load. It is shown in figure.

IV.Procedure

Preliminary Set-up

Switched off all power by setting the 3 phase circuit breaker on the

Universal Power Supply to the off position. Make the connections according tothe circuit figures.

Control Settings

Resistance Box: Fit the link, which shorts out the resistance box, and check

that all the resistances switches are switched on.

Power Supply: Turn the variable output voltage, control to 0%. Switch off the

3 phase circuit breaker.

Dynamometer: Switch off the main ac power using the green on/off button.

Set the two rotary controls to their most anti-clockwise position. Connect

the dynamometer to the speed mode socket. Set the demand voltage switch

to +ve. Press the dynamometer power, on button so that the adjacent red LED

is lit.

A. Effect of Field Current on Output Voltage

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1.) On the power supply unit, set the 3 phase circuit breaker to the on

position.

2.) Using dynamometer panel, set the motor speed to 3000 rpm. Ensure the

speed is maintained at 3000 rpm throughout the following procedure.

3.) Starting with the link inserted in the resistance box, enter the output

voltage and the field current into columns 3 and 4 of a copy of the

appropriate results table.

4.) Remove the link and repeat for the values of the resistance shown in

column 1.

5.) Draw a graph of output voltage against field current using the axes

based on gathered data.

B. Effect of Generator Speed on Output Voltage

1.) Insert the link on the resistance box to short it out. On the power supply

unit, set the 3 phase circuit breaker to the on position.

2.) Using the dynamometer panel, set the motor speed to rpm.

3.) Reduce the sped in intervals of approximately 150 rpm at a time from

3000 rpm to 100 rpm and enter the output voltage and speed in the

table of values

4.) Turn the variable output voltage control to 0% on the Universal Power

Supply and switch off the 3-phase circuit breaker.

5.) Draw a graph of output voltage against speed using the axes based on

gathered data

C. Effect of Resistive Load on Output Voltage and Power

1.) Apply the resistive loads across the generator gathered on part A.

2.) On the power supply unit, set the 3 phase circuit breaker to the on

position.

3.) Using dynamometer panel, set the motor speed to 3000 rpm and

maintain this speed throughout the test.

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4.) Measure and record the corresponding load voltage and current.

5.) Turn the variable output voltage control to 0% on the Universal Power

Supply and switch off the 3-phase circuit breaker.

6.) Draw a graph of output power and output voltage against load curent

using the axes based on gathered data

V. Data Result/ Graphs

A. Effect of Field Current on Output Voltage

Resistance Value()

Switch Position Field Current (A) Output Voltage (V)

182 All switches on 0 A O V182 All switches on .12 A 190 V213 Only 3770R off,

all others on

.10 A 180 V

253 1950R off,

all others on

.10 A 178 V

317 All 950R on,

all others off

.09 A 175 V

640 Only 1950R on,

all others off

.06 A 171 V

950 One 950R on,

all others off

.05 A 150 V

1285 One 1950R & 3770R

on,

all others off

.02 A 130 V

1885 Two 3770R on,

all others off

0 A 12 V

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B. Effect of Generator Speed on Output Voltage

Speed (rpm) Output Voltage (V)

2495 188 V

2215 150 V

1945 120 V

1764 97 V

1662 84 V

1619 64 V

1458 53 V

1386 42 V

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1296 20 V

C. Effect of Resistive Load on Output Voltage and Power

Resistance

Value ()

Switch

Positions

Load Current

(A)

Output

Voltage (V)

Output Power

(W)182 All switches on .8 A 154 V 123.2 W213 Only 3770R

off, all otherson

.7 A 160 V 112 W

253 1950R off, allothers on

.6 A 165 V 99 W

317 All 950R on, allothers off

.5 A 170 V 85 W

640 Only 1950Ron, all others

off

.25 A 180 V 45 W

950 One 950R on,all others off

.2 A 183 V 36.6 W

1285 One 1950R &3770R on, all

others off

.1 A 185 V 18.5 W

1885 Two 3770R on,all others off

.1 A 185 V 18.5 W

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VI.Analysis

VII. Conclusion