Government Engineering College

Kozhikode-5

Electrical Machines Lab ManualAI09 308(P), ME09 307(P)

(Version 1.1.0 - June 25, 2012)

Prepared by :- Mohammed Sadik.P.K(2010 AEI batch)Ranjith A.R (2010 AEI batch)Nikhil Narayanan (2010 AEI batch)

Guided by :- Smt. Sangeetha K (Associate Professor(EEE))

Type set in LATEX2, circuit designs and graphs in XCircuit.Platform : GNU/LinuxOther free softwares used: GNU Emacs, GNU Bash, Gedit, Vim . . . . . .

2011, 2012, Some Rights Reserved.

You may get a copy of this work from www.sadiq.tk.

This work is licensed under :Creative Commons Attribution-ShareAlike 2.5 India License.To view a copy of this license, visit http://creativecommons.org/licenses/by-sa/2.5/in/or send a letter to Creative Commons, 444 Castro Street, Suite 900, Mountain View,California, 94041, USA.

Thanks to:-

1. Smt. Sangeetha K(Associate Professor(EEE))2. Sri. Asokan (Assistant Professor(EEE))3. Dr. Reena P(Associate Professor(ECE))4. Najmudheen P.K (Cherumukku)5. Jazeel M (Kolappuram)6. Selil C.P(MES Kuttippuram-EC)7. Mansoor M (GECK-2008 AEI batch)8. Sajith P.P (GECK-2010 AEI batch)9. Misthah K.M (AWH Kozhikode-EEE)

Our sinere thanks to everyone who have helped us for the perfetion of this

Manual, espeially our lassmates - 2010 AEI bath.

http://www.sadiq.tkhttp://creativecommons.org/licenses/by-sa/2.5/in/

CONTENTS

1. Load test on single phase transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2. Load test on 3 squirrel cage induction motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3. O.C.C of dc shunt generator. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

4. Load test on dc shunt generator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5. Load test on dc series motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

6. Measurement of coupling coefficient of transformer coils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

7. O.C and S.C tests on single phase transformer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34

8. Three phase power measurement by two wattmeter method. . . . . . . . . . . . . . . . . . . . . . . . . . .42

9. Calibration of single phase energy meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46

10. Resistance measurement using Wheatstones bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

11. Resistance measurement using Kelvins double bridge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

12. V-I Characteristics of incandescent lamp and linear resistance . . . . . . . . . . . . . . . . . . . . . . . . 58

13. Open circuit and short circuit test on three phase alternator . . . . . . . . . . . . . . . . . . . . . . . . . . 60

14. No load and blocked rotor tests on 3 slip ring induction motor. . . . . . . . . . . . . . . . . . . . .64

3

CONNECTION DIAGRAM OF LOAD TEST

A A

V V

M

C

L

V P1

P2 S2

S1

Load

230V

1 - 50 HzAC

NL

10A

0-150V

0-10A MI 150V,10A,upf 0-5A MI

0-250VC

S

MI

N

P

120/240V 1KVATRANSFORMER

E

B

MI

Rated current on primary side =1000

120= . . . . . .

Rated current on secondary side =1000

240= . . . . . .

REGULATION AND EFFICIENCY CURVES

Reg

ulat

ion

(%)

Eff

icie

ncy

(%)

Output (watts)

Regulation

Efficiency

Experiment 1 4

Experiment 1

LOAD TEST ON SINGLE PHASE

TRANSFORMER

AIM

To conduct load test on the given single phase transformer at unity power factor and determine

the efficiency and regulation curve.

APPARATUS REQUIRED

1. Voltmeter 0-250V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.

2. Voltmeter 0-150V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.

3. Ammeter 0-10A MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.

4. Ammeter 0-5A MI. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 no.

5. Wattmeter 150V, 10A, upf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.

6. Autotransformer(cont. variable) 0-270V, 10A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.

THEORY

Regulation of a transformer is defined as the drop in terminal voltage of a transformer expressed

as a percentage of the no-load terminal voltage.

%Regulation =Vno load Von load

Vno load

When a purely resistive load is connected across the secondary, the transformer will be

working at unity power factor.

Terminal voltage, V = Induced emf [E2] I2r2 I2x2

Where r2 and x2 are the secondary winding resistance and leakage reactance respectively

and I2 is the secondary load current.

The efficiency of transformer is defined asOutput

Input 100.

As the load current increases the power output increases. The iron loss remains constant

from no load to full load. The copper loss increases as the square of the load current. Thus the

efficiency curve starts from zero, increases to a maximum value(When iron loss = Cu loss) and

thereafter starts decreasing.

5

OBSERVATION

Sl. V1 I1 W1 V2 I2 Output Efficiency RegulationNo. (volts) (Amp) (watts) (volts) (Amp) (watts) (%) (%)

V2 at no load = VNL = . . . . . .

Sample Calculation (set no . . . )

Primary Voltage (V1) = . . . . . . . . .

Primary Current (I1) = . . . . . . . . .

Wattmeter Reading (W1)= Input power = . . . . . . . . .

Secondary Voltage (V2) = . . . . . . . . .

Secondary Current (I2) = . . . . . . . . .

Output = I2V2 = . . . . . . . . .

Efficiency =Output power

Input power100= . . . . . . . . .

Regulation =VNL VL

VNL100 = . . . . . . . . .

6

PROCEDURE

Connections are made as shown in the circuit diagram. The supply is switched on keeping

the autotransformer in the minimum position and at no load. Adjust the autotransformer to

get the rated voltage of the transformer. The readings of all the meters are noted down. The

secondary voltage at no load is also noted down. This value is VNL. A small load is added

on the secondary side and the meter readings are again noted. The experiment is repeated

for different values of load current till the current on the primary side equals the rated value.

The load is then reduced to zero, the autotransformer is brought back to the zero position and

the supply is switched off. The readings are then tabulated as shown and the regulation and

efficiency curves are plotted.

RESULT

Conducted load test on the given 1- transformer and plotted the regulation and efficiency

curves.

VIVA QUESTIONS

1. What do you understand by regulation of a transformer?

2. What are the other methods of testing transformers?

3. What is the disadvantage of testing a transformer using load test?

4. Is a high or low value of regulation preferred for a transformer? Give reasons.

5. What are the reasons for the drop in terminal voltage as the secondary current

is increased?

7

CONNECTION DIAGRAM

400V

3 -

50

Hz

AC

10A

D.O.LSTARTER

0-600VMI

0-10A MI 600V,10A,upf

C

M

V

L

IM

600V,10A,upf

10A

10A M

C V

L

V

AR

Y

B

B

Y

RS1 S2

MACHINE DETAILS

Voltage V - 415 VCurrent I - 7.5APower - 5HPConnection - Speed(rpm) - 1440Phase - 3

Synchronous speed =120f

P

=120 50

4

= 1500 rpm

Experiment 2 8

Experiment 2

LOAD TEST ON 3 SQUIRREL CAGEINDUCTION MOTOR

AIM

To conduct load test on the given 3- squirrel cage induction motor and plot the performance

characteristics.

APPARATUS REQUIRED

1. Voltmeter 0-600V MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.

2. Ammeter 0-10A MI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 no.

3. Wattmeter 600V,10A, upf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 nos.

4. Tachometer To measure speed

THEORY

A squirrel cage induction motor essentially consists of a stator and a rotor. The stator is a

hollow cylindrical structure with slots on the inner periphery and carries a three phase winding.

The winding can be connected in star or delta and is connected across a 3- supply.

The rotor is also a cylindrical structure with slots on the outer periphery. The slots carry

thick Al or Cu bars. These bars are short circuited at both ends by means of end rings.

When a 3- supply is given to a 3- winding displaced by 120