st semester laboratory manual of electrical machines...

CHRISTU JYOTI INSTITUTE OF TECHNOLOGY & SCIENCE Colombonagar,Janagoan,Warangal

ANDHRA PRADESH-506167

2013-14 1st Semester

LABORATORY MANUAL of

ELECTRICAL MACHINES II

Prepared by

P.ANIL KUMAR

Assistant Professor

for

III B.Tech EEE

DEPARTMENT OF

ELECTRICAL & ELECTRONICS ENGINEERING

Electrical Machines-II Lab Manual

2

INDEX

Page No

List of experiments as per university

3

List of experiments to be conducted for this

semester

4

Cycle indicate schedule and the batch size 5-7

Laboratory Practice Safety Rules

Guidelines For Laboratory Notebook

8-10

Sl. No Experiment Name

1. OC & SC test on single phase transformer

11-16

2. Sumpners’s test on a pair of single phase transformer

17-22

3. No-load & Blocked rotor tests on three phase induction

motor

23-26

4. Separation of core losses of a single phase transformer

27-30

5. Efficiency of a three phase alternator

31-34

6. Brake test on three phase induction motor

35-38

7. Regulation of a three phase alternator by synchronous

impedance & m.m.f methods

39-43

8. V and inverted V curves of a three phase synchronous

motor

44-47

9. Equivalent circuit of a single phase induction motor

48-51

10. Determination of Xd and Xq of a Salient pole

synchronous machine

52-55

Additional Experments 11. Scott connection of Transformers. 56-60

12. Parallel Operation of Two Single Phase Transformers. 61-63


3

JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY

III Year B.Tech EEE ISem Academic year 2013-2014

L T/P/D C

0 -/3/- 2

(55602) ELECTRICAL MACHINES LAB –II

The following experiments are required to be conducted as compulsory experiments.

1. O.C. & S.C. Tests on single phase transformer.

2. Sumpner's test on a pair of single phase transformers.

3. Brake test on three phase squirrel cage induction motor.

4. No-load & blocked rotor tests on three phase Slip ring Induction motor.

5. Regulation of a three phase alternator by synchronous impedance (EMF & MMF) method.

6. V and inverted V curves of a three - phase Synchronous motor.

7. Equivalent circuit of a single phase induction motor.

8. Determination of Xd and Xq of a salient pole synchronous machine.

In addition to the above experiments, at least any two of the experiments from the

following list are required to be conducted.

1. Parallel Operation of Single Phase Transformers.

2. Separation of core losses of a single phase transformer.

3. Scott connection of Transformers.

4. Regulation of a three phase alternator by ZPF & ASA method.

5. Efficiency of a tree phase alternator.

6. Heat run test on a bank of 3 Nos of single phase delta connected transformers.

7. Measurement of sequence Impedance of a 3phase alternator.


4

Experiments Conducted by the Department:-

1. O.C. & S.C. Tests on single phase transformer .

2. Sumpner's test on a pair of single phase transformers .

3. No-load & Blocked rotor tests on three phase induction motor

4. Separation of core losses of a single phase transformer

5. Efficiency of a three phase alternator

6. Brake test on three phase induction motor

7. Regulation of a three phase alternator by synchronous impedance & m.m.f methods

8. V and inverted V curves of a three phase synchronous motor

9. Equivalent circuit of a single phase induction motor

10. Determination of Xd and Xq of a Salient pole synchronous machine

Additional Experments

1. Parallel Operation of Two Single Phase Transformers.

2. Measurement of sequence Impedance of a 3phase alternator.

3. Scott connection of Transformers.


5

FIRST CYCLE EXPERIMENTS:

Experiment No. Experiment Name

1 OC & SC test on single phase transformer

2 Sumpners’s test on a pair of single phase transformer

3 No-load & Blocked rotor tests on three phase induction motor

4 Separation of core losses of a single phase transformer

5 Efficiency of a three phase alternator

SECOND CYCLE EXPERIMENTS :

Experiment No. Experiment Name

6 Brake test on three phase induction motor

7 Regulation of a three phase alternator by synchronous impedance & m.m.f

methods

8 V and inverted V curves of a three phase synchronous motor

9 Equivalent circuit of a single phase induction motor

10 Determination of Xd and Xq of a Salient pole synchronous machine


6

LABORATORY PRACTICE

SAFETY RULES

SAFETY is of paramount importance in the Electrical Engineering Laboratories.

2.Electricity NEVER EXECUSES careless persons. So, exercise enough care and attention

in handling electrical equipment and follow safety practices in the laboratory. (Electricity

is a good servant but a bad master).

3.Avoid direct contact with any voltage source and power line voltages. (Otherwise, any such

contact may subject you to electrical shock)

4.Wear rubber-soled shoes. (To insulate you from earth so that even if you accidentally

contact a live point, current will not flow through your body to earth and hence you will be

protected from electrical shock)

5.Wear laboratory-coat and avoid loose clothing. (Loose clothing may get caught on an

equipment/instrument and this may lead to an accident particularly if the equipment

happens to be a rotating machine)

6.Girl students should have their hair tucked under their coat or have it in a knot.

7.Do not wear any metallic rings, bangles, bracelets, wristwatches and neck chains. (When

you move your hand/body, such conducting items may create a short circuit or may touch a

live point and thereby subject you to electrical shock)

8.Be certain that your hands are dry and that you are not standing on wet floor. (Wet parts of

the body reduce the contact resistance thereby increasing the severity of the shock)

9.Ensure that the power is OFF before you start connecting up the circuit.(Otherwise you will

be touching the live parts in the circuit)

10.Get your circuit diagram approved by the staff member and connect up the circuit strictly

as per the approved circuit diagram.

11.Check power chords for any sign of damage and be certain that the chords use safety

plugs and do not defeat the safety feature of these plugs by using ungrounded plugs.

12.When using connection leads, check for any insulation damage in the leads and avoid

such defective leads.

13.Do not defeat any safety devices such as fuse or circuit breaker by shorting across it.

Safety devices protect YOU and your equipment.

14.Switch on the power to your circuit and equipment only after getting them checked up

and approved by the staff member.

15.Take the measurement with one hand in your pocket. (To avoid shock in case you

accidentally touch two points at different potentials with your two hands)

16.Do not make any change in the connection without the approval of the staff member.

17.In case you notice any abnormal condition in your circuit ( like insulation heating up,

resistor heating up etc ), switch off the power to your circuit immediately and inform the

staff member.

18.Keep hot soldering iron in the holder when not in use.

19.After completing the experiment show your readings to the staff member and switch off

the power to your circuit after getting approval from the staff member.

20.While performing load-tests in the Electrical Machines Laboratory using the brake-

drums:Avoid the brake-drum from getting too hot by putting just enough water into the

brake-drum at intervals; use the plastic bottle with a nozzle (available in the laboratory ) to

pour the water.(When the drum gets too hot, it will burn out the braking belts)

Do not stand in front of the brake-drum when the supply to the load-test circuit is switched

off. (Otherwise, the hot water in the brake-drum will splash out on you)

After completing the load-test, suck out the water in the brake-drum using the plastic

bottle with nozzle and then dry off the drum with a sponge which is available in the


7

laboratory.(The water, if allowed to remain in the brake-drum, will corrode it)

21.Determine the correct rating of the fuse/s to be connected in the circuit after

understanding correctly the type of the experiment to be performed: no-load test or full-

load test, the maximum current expected in the circuit and accordingly use that fuse-

rating.(While an over-rated fuse will damage the equipment and other instruments like

ammeters and watt-meters in case of over load, an under-rated fuse may not allow one

even to start the experiment)

22. At the time of starting a motor, the ammeter connected in the armature circuit overshoots,

as the starting current is around 5 times the full load rating of the motor. Moving coil

ammeters being very delicate, may get damaged due to high starting current. A switch has

been provided on such meters to disconnect the moving coil of the meter during starting.

This switch should be closed after the motor attains full speed. Moving iron ammeters

and current coils of watt meters are not so delicate and hence these can stand short time

overload due to high starting current. No such switch is therefore provided on these

meters. Moving iron meters are cheaper and more rugged compared to moving coil

meters. Moving iron meters can be used for both a.c. and d.c. measurement. Moving coil

instruments are however more sensitive and more accurate as compared to their moving

iron counterparts and these can be used for d.c. measurements only. Good features of

moving coil instruments are not of much consequence for you as other sources of errors in

the experiments are many times more than those caused by these meters.

23. Some students have been found to damage meters by mishandling in the following ways:

Keeping unnecessary material like books, lab records, unused meters etc. causing meters

to fall down the table.

Putting pressure on the meter (specially glass) while making connections or while talking

or listening somebody.

STUDENTS ARE STRICTLY WARNED THAT FULL COST OF THE METER WILL BE

RECOVERED FROM THE INDIVIDUAL WHO HAS DAMAGED IT IN SUCH A

MANNER.

Copy these rules in your Lab Record. Observe these yourself and help your friends to observe

I have read and understand these rules and procedures. I agree to abide by these rules and

procedures at all times while using these facilities. I understand that failure to follow these

rules and procedures will result in my immediate dismissal from the laboratory and additional

disciplinary action may be taken.

GUIDELINES FOR LABORATORY NOTEBOOK

The laboratory notebook is a record of all work pertaining to the experiment. This record

should be sufficiently complete so that you or anyone else of similar technical

background can duplicate the experiment and data by simply following your laboratory

notebook. Record everything directly into the notebook during the experiment. Do not use

scratch paper for recording data. Do not trust your memory to fill in the details at a later time.

Organization in your notebook is important. Descriptive headings should be used to separate

and identify the various parts of the experiment. Record data in chronological order. A neat,

organized and complete record of an experiment is just as important as the experimental

work.


8

1. Heading:

The experiment identification (number) should be at the top of each page.Your name

and date should be at the top of the first page of each day's experimental work.

2.Object:

A brief but complete statement of what you intend to find out or verify in the

experiment should be at the beginning of each experiment

3.Diagram:

A circuit diagram should be drawn and labeled so that the actual experiment circuitry

could be easily duplicated at any time in the future. Be especially careful to record all

circuit changes made during the experiment.

4.Equipment List:

List those items of equipment which have a direct effect on the accuracy of the data. It

may be necessary later to locate specific items of equipment for rechecks if discrepancies

develop in the results.

5.Procedure:

In general, lengthy explanations of procedures are unnecessary. Be brief. Short

commentaries along side the corresponding data may be used. Keep in mind the fact that the

experiment must be reproducible from the information given in your notebook.

6.Data:

Think carefully about what data is required and prepare suitable

data tables. Record instrument readings directly. Do not use calculated results in place

of direct data; however, calculated results may be recorded in the same table with the direct

data. Data tables should be clearly identified and each data column labeled and headed by the

proper units of measure.

7.Calculations:

Not always necessary but equations and sample calculations are often given to

illustrate the treatment of the experimental data in obtaining the results.

8.Graphs:

Graphs are used to present large amounts of data in a concise visual form. Data to be

presented in graphical form should be plotted in the laboratory so that any questionable

data points can be checked while the experiment is still set up. The grid lines in the notebook

can be used for most graphs. If special graph paper is required, affix the graph

permanently into the notebook. Give all graphs a short descriptive title. Label and scale

the axes. Use units of measure. Label each curve if more than one on a graph.

9.Results:

The results should be presented in a form which makes the interpretation easy. Large

amounts of numerical results are generally presented in graphical form. Tables are

generally used for small amounts of results. Theoretical and experimental results should be

on the same graph or arrange in the same table in a way for easy correlation of these results.

10.Conclusion:

This is your interpretation of the results of the experiment as an engineer. Be brief

and specific. Give reasons for important discrepancies.


9

EXP.NO. 01 DATE:

1. OC & SC TESTS ON 1- Φ TRANSFORMER

AIM: To conduct OC & SC tests on the given 1- Transformer and to calculate its

1) Equivalent circuit parameters

a). Referred to H.V side

b). Referred to L.V side

2) Efficiency at various loads.

3) Regulation at various power factors

4) Maximum Efficiency.

NAME PLATE DETAILS: 1Φ - TRANSFORMER

T/F

LV side HV side

Rated power

Rated voltage

Rated current

Frequency

APPARATURS REQUIRED:

SL.NO Name of the Apparatus Type Range Quantity

1 Ammeter MI

2 Ammeter MI

3 Voltmeter MI

4 Voltmeter MI

5 Wattmeter EDM(LPF)

6 Wattmeter EDM(UPF)

7 Dimmerstat


10

CIRCUIT DIAGRAM:

THEORY:-

Open – Circuit (OC) or No-Load Test

The purpose of this test is to determine the shunt branch parameters of the equivalent circuit of the

transformer. One of the windings is connected to supply at rated voltage, while the other winding is

kept open - circuited. From the point of view of convenience and availability of supply the test is

usually performed from the LV side, while the HV side is kept open circuited.

Voltage = V1; Current = I0 and power input = P0

Indeed the no-load current, I0 is so small (it is usually 2-6% of the rated current) and R 01 and X 01 are

also small, that V1 can be regarded as = E1 by neglecting the series impedance. This means that for all

practical purposes the power input on no-load equals the core (iron) loss i.e.,

P0 = V1 I0cos0

cos0 = P0 / V1 I0

A

V

0-1A,

MI

0-150V

,MI

2KVA

240 / 415 V

O

C

LV H

V

A

V

0-10 A

MI

0-30 V

,MI

2KVA

415 /240 V

LV

S

C

H

v

V

V

150V,1 0 A,

UPF M L

C V

M L

C V

•

•

•

•

CIRCUIT DIAGRAM: OC AND SC TESTS ON A SINGLE PHASE

TRANSFORMER

N

230/ 0-

270V

Variac 230V,

1-

φ,50Hz

AC

Supply

||

||

||

||

||

||

||

||

||

||

||

Ph

230/ 0-

270V

Variac 230V,

1-

φ,50Hz

AC

Supply

||

||

||

||

||

||

||

||

||

||

||

Ph

N

300V ,5 A L,

PF

D

P

S

T

D

P

S

T

1A

1

A

5

A

5

A


11

Iw = I0cos0, I = I0sin0

R0 = V1/ Iw , X0 = V1 / I

Short Circuit (SC) Test

This test serves the purpose of determining the series parameters of a

transformer. For convenience of supply arrangement and voltage and current to be

handled, the test is usually conducted from the HV side of the transformer while the

LV side is short-circuited. Since the transformer resistance and leakage reactance are

very small, the voltage Vsc needed to circulate the full load current under short circuit

is as low as 5-8% of the rated voltage. The exciting current under these conditions is

only about 0.1to 0.5% of the full load current Thus the shunt branch of the equivalent

circuit can be altogether neglected. While conducting the SC test, the supply voltage is

gradually raised from zero till the transformer draws full load current. The meter

readings under these conditions are: Since the transformer is excited at very low

voltage, the iron loss is negligible (that is why shunt branch is left out ), the power

input corresponds only to the copper loss, i.e

Vsc =Voltage, Isc = Current , Psc = Power (Copper loss)

Z 01= VSC / ISC = R 012 + X 01

2

Equivalent resistance, R01= PSC / (ISC)2

Equivalent reactance, X 01 = Z 012 – R 01

2

PROCEDURE :

OC TEST :

(1) All the connections are done as per the circuit diagram of OC test

(2) By using 1- variac apply rated voltage to the circuit.

(3) At this rated voltage note down voltmeter, ammeter & wattermeter readings.

(4) From the values we can find R0 and X0

SC TEST :

(1) All the connections are done as per the circuit diagram of SC test

(2) By using 1- variac rated current is made to flow in the circuit.

(3) At this rated current note down voltmeter, ammeter & wattermeter readings.

(4) From this values we can find out R01 & X01

PRECAUTIONS :

(1) Open circuit test is performed on LV side i.e meters are connected LV side and HV side will be

open circuited.

(2) For short circuit test is connect meters on HV side and LV side will be short circuited

(3) Rated voltage and rated current must be maintained in OC test and SC test respectively


12

(4) All the connections must be tight

TABULAR COLUMNS

Observations: OC TEST:

SC TEST:

CALCULATIONS: Efficiency vs Load %LOAD

Power factor lagging

0.2

0.4

0.6

0.8

1

25

50

75

Vo

Volts

Io

Amps

Wo

Watts

Vsc

Volts

Isc

Amps

Wsc

Watts


13

100

125

Regulation %LOAD

Power factor laging UPF Power factor leading

0.2

0.4

0.6

0.8

1

0.8

0.6

0.4

0.2

25

50

75

100

125

EQUALENT CIRCUIT:

MODEL GRAPHS

V1 =240V

R02 X02

R

0

X0 E

1

Regulation

Regulation

Pf

leading Pf lagging lea

d


14

RESULT:


15

EXP.NO. 02 DATE:

1. SUMPNER’S TEST ON A PAIR OF 1-Ф TRANSFORMER

AIM: To conduct OC & SC tests on the given 1- Transformer and to calculate its

1) Equivalent circuit parameters

a). Referred to H.V side

b). Referred to L.V side

2) Efficiency at various loads.

3) Regulation at various power factors

4) Maximum Efficiency.

NAME PLATE DETAILS:

1Φ - TRANSFORMERs

T/F T/F-1 T/F-2

LV side HV side HV side LV side

Rated power

Rated voltage

Rated current

Frequency



16


1 Ammeter MI

2 Ammeter MI

3 Voltmeter MI

4 Voltmeter MI



7 Dimmerstat

THEORY:-

Without conducting any actual loading test is the Sumpner’s test which can only

be conducted simultaneously on two identical transformers. In conducting the Sumpner’s test

the primaries of the two transformers are connected in parallel across the rated voltage

supply(V1), while the two secondaries are connected in phase opposition. As per the

superposition theorem, if V2 source is assumed shorted, the two transformers appear in open-

circuit to source V1 as their secondries are in phase opposition and therefore no current can

flow in them. The current drawn from source V1 is thus 2I0 (twice the no-load current of each

transformer) and power is 2P0 (= 2Pi , twice the core loss of each transformer). When V1 is

regarded as shorted, the transformers are series-connected across V2 and are short-circuited

on the side of primaries. Therefore, the impedance seen at V2 is 2Z and whenV2 is adjusted to

circulate full-load current (Ifl), the power fed in is 2Pc (twice the full-load copper-loss of each

transformer). Thus in the Sumpner’s test while the transformers are not supplying any load,

full iron-loss occurs in their core and full copper-loss occurs in their windings; net power

input to the transformers being(2Po+2Pc).The heat run test could , therefore, be conducted on

the two transformers, while only losses are supplied.

For each trans former the results are

Voltage =V1 , Current = I0 /2 , Core losses = P0 /2

Voltage =Vsc /2 , Current = Isc , Copper losses = Psc /2

P0 = Pi (iron-loss)

P0 = V1 I0cos0

cos0 = P0 / V1 I0


17

Iw = I0cos0, I = I0sin0

R0 = V1/ Iw , X0 = V1 / I.

Vsc =Voltage, Isc = Current , Psc = Power (Copper loss)

Z 01= 2

scV / ISC = R 012 + X 01

2

Equivalent resistance, R01= 2

scP / (ISC)2

Equivalent reactance, X 01 = Z 012 – R 01

2

CIRCUIT DIAGRAM:

PROCEDURE :

(1) Connections are done as per the circuit diagram.

(2) By using the variac rated voltage is 240V is made to apply across the low voltage side

of the transformer.

0-300V,MI

0-1A,MI

0-150V,MI

0-10A,MI

0-600V,MI

• 0 415 V 415 V

0

240 V 240V

2KVA

240/415

V

230/0-270V

Variac

300V,10A,LPF

230/ 0-

270V

Variac

C V

150V,10A,UPF

M L

M L

C V

230V,

1-

φ,50Hz

AC

Supply

||

||

||

||

||

||

||

||

||

||

||

||

N

Ph

230V,

1-

φ,50Hz

AC

Supply

||

||

||

||

||

||

||

||

||

||

||

||

N

Ph

A

A

V

V

V

||

||

||

||

||

||

||

||

||

||

NAME PLATE

DETAILS:

D

P

S

T

D

P

S

T

D

P

S

T

1 A

1 A

5 A


18

(3) Before closing the DPST switch the reading of the voltmeter connected across DPST

switch must be zero.

(4) By using the variac in H.V side rated current is made to flow in the circuit.

(5) At this instant note down all the meter readings.

(6) By using above tabulated readings the efficiency and regulation of the transformers

are calculated.

RECAITIONS:

1) The Dimmer stat should be kept at minimum O/P position initially.

2) The Dimmer stat should be varied slowly & uniformly.

TABULAR COLUMNS

Observations: Primary Side:

Secondary Side:

CALCULATIONS: Efficiency vs Load

Power factor lagging

Vo

Volts

2Io

Amps

2Wo

Watts

2Vsc

Volts

Isc

Amps

2Wsc

Watts


19

%LOAD

0.2

0.4

0.6

0.8

1

25

50

75

100

125

Regulation: %LOAD

Power factor laging UPF Power factor leading

25

50

75

100

125

EQUALENT CIRCUIT:

MODEL GRAPHS

V1 =240V

R02 X02

R

0

X0 E

1

Regulation

Pf Pf lagging lead


20

RESULT:


21

EXP.NO.3 DATE:

NO LOAD AND BLOCKED ROTOR TEST ON 3- PHASE INDUCTION MOTOR

AIM: To conduct the no load & blocked rotor test on 3- phase induction motor

& to draw the equivalent circuit of 3- phase squirrel cage induction motor.

NAME PLATE DETAILS:

Parameters Induction Motor

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUS REQUIRED:

S.No Name of apparatus Type Range Qty.

1. Ammeter MI

2. Voltmeter MI

3. Wattmeter EDM


22

4. Tachometer digital

5. Connecting Wires

THEORY :

A 3-phase induction motor consists of stator, rotor & other associated parts. In the stator

,a 3- phase winding (provided) are displaced in space by 120. A3- phase current is fed to the

winding so that a resultant rotating magnetic flux is generated. The rotor starts rotating due to

the induction effect produced due the relative velocity between the rotor

Winding & the rotating flux.

As a general rule, conversion of electrical energy to mechanical energy takes place in to the

rotating part on electrical motor. In DC motors, electrical power is conduct directly to the

armature, i.e, rotating part through brushes and commutator. Hence, in this sense, a DC motor

can be called as 'conduction motor'.

However, in AC motors, rotor does not receive power by conduction but by induction in

exactly the same way as secondary of a two winding T/F receives its power from the primary.

So, these motors are known as Induction motors. In fact an induction motor can be taken as

rotating T/F, i.e, one in which primary winding is stationary and but the secondary is free.

The starting torque of the Induction motor can be increase by improving its p.f by adding

external resistance in the rotor circuit from the stator connected rheostat, the rheostat resist

ance being progressively cut out as the motor gathers speed. Addition of external resistance

increases the rotor impedance and so reduces the rotor current. At first, the effect of improved

p.f predominates the current decreasing effect of impedance. So, starting torque is increased.

At time of starting, external resistance is kept at maximum resistance position and after a

certain time, the effect of increased impedance predominates the effect of improved p.f and

so the torque starts decreasing. By this during running period the rotor resistance being

progressively cut-out as the motor attains its speed. In this way, it is possible to get good

starting torque as well as good running torque.

CIRCUIT DIAGRAM:


23

PROCEDURE :

NO LOAD TEST :

(1). Connections are given as per the circuit diagram.

(2). Precautions are observed and motor is started on the no load.

(3). Autotransformer is varied to have rated voltage applied.

(4). The meter readings are then tabulated.

BLOCKED ROTOR TEST :

(1). Connections are given as per circuit diagram.


24

(2). Precautions are observed and motor is started on full load or blocked rotor position.

(3). Autotransformer is varied to have rated current flowing in motor.

(4). The meter readings are then tabulated.

PRECAUTIONS :

NO LOAD TEST:

(1). Initially TPST switch is kept open.

(2). Autotransformer must be kept at minimum potential position.

(3). The machine must be started at no load.

BLOCKED ROTOR TEST:

(1). Initially the TPST switch is kept open.

(2). Autotransformer must be kept at minimum potential position.

(3). The machine should be started on full load.

FORMULA USED:

FOR NO LOAD TEST:

Wsc = √3 Vo IoCOSФ watts

Iw = Io cosФ amps

Ro= V0/ Iw Ω

Xo= Vo/Iu Ω

FOR BLOCKED ROTOR TEST:

Wsc =3I2*Ro watts

Ro1 = Wsc/3(Isc)2 Ω

Zo1 = Vsc/Isc Ω

Xo1 = √Zo1^2-Ro1^2 Ω

TABULAR COLUMNS:

NO LOAD TEST:

Voltage

Voc

Volts

Current

Ioc

Amps

Wattmeter

readings (W1)

Wattmeter

readings

(W2)

Toyal

Power

Wo

(W1-W2)

cosΦo=

Wo/

(3 Voc

Ioc)

Φo=

Voc= open circuit voltage


25

Ioc = open circuit current

BLOCKED ROTOR TEST:

Voltage

Vsc

Volts

Current

Isc

Amps

Wattmeter

readings (W1)

Wattmeter

readings

(W2)

Toyal Power

Wsc

(W1-W2)

cosΦo=

Wsc/

( 3Vsc

Isc)

Φsc=

Vsc = short circuit voltage

Isc = short circuit current

GRAPH:

RESULT: Hence by conducting the no load & blocked rotor test of 3- phase induction

motor

EXP.NO. 04 DATE:

SEPERATION OF CORE LOSSES 1- TRANSFORMER

AIM : To separate hysteresis and eddy current losses of a given 1- transformer.

NAME PLATE DETAILS:

DC Motor Alternator Transformer

Rated Power

Rated voltage


26

Rated current

Rated speed

Rated field current

APPARATUS REQUIRED:


1 Ammeter MC

2 Voltmeter MI

3 Wattmeter EDM

4 Rheostat Wire wound

5 Potential Divider Wire wound

6 Tachometer Digital

THEORY :-

Hysteresis and eddy current losses are called iron loss and take place in core of the

transformer .

Hysteresis loss is given by = Wh = KBmox1.6

f = Af

Eddy current loss also depends on the frequency f and is given by

We = KB2

mox f2

t2 =Bf

2

B max = Maximum flux density weber / m2

F = frequency cycles/ seconds

t = thickness of stamping

The iron loss will be expressed by

W i = Af +B f2

W i/ f = A + B f

, y = m x + c

This is equation of straight line y = m x + c, when y = w i / f , c = A , and m = B

and x = f.

Eddy current and Hysteresis loss can be separated when A and B are found.

The variable frequency supply is obtained from an alternator when frequency can be

varied.

CIRCUIT DIAGRAM:

360Ω

1.2A

X

XX

Z

145Ω

2.8A

145 Ω

2.8A

L A F

R

B Y

18Ω/12A

•

220V ,DC

Supply

||

||

||

||

||

||

||

||

||

||

||

+

3 Pt starter

10 A

D

P

S

T

AA

M A


27

PROCEDURE :


(2) Initially rheostat in the armature circuit of motor is kept at maximum position, the

rheostat in the field circuit of motor is kept at minimum position and the rheostats in the

field circuit (potential divider)of the alternator are kept so that minimum voltage is

applied to the field circuit of the alternator.

(3) Start the motor with the help of 3-point starter

(4) Bring the speed of the motor to the rated speed by using the rheostats of the motor.

(5) By increasing the excitation of alternator using the potential divider bring the voltage of

the alternator to the rated voltage.

(6) Apply the rated voltage to the high voltage side of the transformer by closing the DPDT

switch.

(7) Note down all the meter readings and speed.

(8) Alternator is made to run at different speeds below the rated speed and adjust the voltage

of the alternator, so that v / f ratio is constant.

(9) At each and every speed, note down the readings of voltmeter, ammeter, wattmeter and

the speed of the motor.

(10) Perform the experiment up to 80% of the rated speed and graphs are drawn between


28

(i) Wi / f Vs f (ii) losses Vs f

TABULAR FORM :

S.no Voltage

(V)

Wattmeter

reading (W)

Speed

(rpm) f = PN / 120

V/f Wi / f

1

2

3

4

5

6

7

8

9

10

11

12

MODEL GRAPH

PRECAUTIONS :

(1) Care must be taken about the v / f value constant so that the flux density is maintained

constant.

(2) The rheostat in the field circuit of motor should be minimum position, the rheostat in the

armature circuit of motor should be maximum position and potential divider of alternator

should give voltage to the alternator at the time of starting.

f

W / f

A


29

RESULT : Separate hysteresis and eddy current losses of a given 1- transformer are

obtained as follows:

Eddy current losses=

Hysteresis losses =

Total Core losses =

EXP.NO. 05 DATE:

5. EFFICIENCY OF A THREE PHASE ALTERNATOR

Aim:-To conduct a suitable test on the given alternator and to determine the efficiency of a

three phase alternator.

Name Plate Details:-

Serial Number Parameters DC Shunt Motor Alternator

1 Rated Voltage

2 Rated Current

3 Rated Speed


30

4 Rated Power

5 Rated Field Current

ApparatusRequired:-

Serial Number Item Type Range Quantity

1 Voltmeter MI&MC

2 Ammeter MI&MC

3 Rheostat Wire wound


5 Potential Divider wirewound

6 Connecting

Wires

Theory:-

Just as in case of generator the input to the alternator is not readily measured .The

direct measurement of efficiency of actual loading is accompanied by different difficulties of

providing the necessary power and finding suitable load .Efficiency is therefore determined

by measuring the losses of the machinery .The losses in alternator are as follows :-

a) Electrical Losses: - This includes field loss, armature winding loss, and brush contact

loss. The copper loss in the field circuit is obtained by adding If2Rf loss of field

winding and the electrical loss of field rheostat or more simply by multiplying the

excitation voltage by current. This loss is constant for any given voltage and power


31

factor but varies with to. The maintenance of rated voltage at low lagging power factor

needs comparatively large field current and gives the maximum field loss.

The armature copper loss in the stator winding is determined on

the basis of armature resistance whether the ohm or the effective resistance should be

used depends on the treatment of stray load loss.

The electrical loss at the brush contacts between brushes and slip

ring is usually quite small and is often neglected.

b) Core Loss: - Due to the eddy currents and hysteresis caused by the flux resulting

from the combined rotor and stator field such losses occur in the pole face and

armature teeth and core. This loss is assumed to be independent of load but varies

with excitation, if the excitation is factor then this loss changes also. It is equal to the

difference of power required to drive the alternator with and without the field excited.

c) Friction and Winding Loss: - It includes ventilation loss (power requirement to

include the cooling air) and loss due to bearing and brush friction. Since the speed is

constant so this loss for particular machine remains constant .It is equal to the

mechanical power required to drive the alternator at rated speed with no excitation.

d) Load or Stray Power Loss: - Loss is due to armature leakage flux which causes eddy

current and hysteresis loss in the iron surrounding the armature conductors in addition

core loss caused by distortion of the magnetic field under load conditions. It may

however be included in the efficiency calculation by using the effective value of R

instead of the dc R.

Procedure:-

i. Couple the dc motor and alternator, run the dc motor above at the rated speed

(Synchronous speed of alternator). For the dc motor record terminal voltage Vo,

armature current Ia ,

For known value of armature circuit resistance Ra

V1I1 = friction and wind age loss of motor +friction and wind age loss of alternator

+ core loss + Ia2Ra...

V1I1=Fwm +Fwa +core + Ia2Ra.

X=V1I1-Ia12Ra

Fw=W1=0.35X

ii. Couple the alternator mechanically with dc motor, run the dc motor again at Ns

with alternator field unexcited .Record V2I2 values

V2I2=X + W2 + Ia22Ra

W2 = V2I2-(X+Ia22Ra)

iii. Field core loss is equal to the product of voltage applied to field winding and

normal field current.

W3=IfVf

iv. Run the dc motor at rated speed, perform three- phase Symmetrical short circuit

test on alternator with short circuit current equal to the rated current of alternator

Record V3, I3 values.

V3I3=X +W4 +Ia32Ra

X


32

W4=V3I3-(X + Ia32Ra)

Total Loss=W1+W2+W3+W4

Efficiency = 𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟

𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟 + 𝑡𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠𝑠

Output =KVA rating X power factor

For maximum efficiency

Output = xscosφ

X = 𝑊1+𝑊2 +𝑊3

𝑊4

Total Loss=2x2W4

Maximum Efficiency =𝑜𝑢𝑡𝑝𝑢𝑡

𝑂𝑢𝑡𝑝𝑢𝑡 +𝑇𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠

Observation:-

V1= I1= Ia1=

V2= I2= Ia2=

VF= IF= Ra=

V3= I3= Ia3=

Calculation:-

V1=

I1=

Ia1=

Ra=

X=V1I1-Ia12Ra

Fw=W1=0.35X

V2I2=X + W2 + Ia22Ra

W2 = V2I2-(X+Ia22Ra)

W3=IfVf

V3I3=X +W4 +Ia32Ra

W4=V3I3-(X + Ia32Ra)

Total Loss=W1+W2+W3+W4

Efficiency = 𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟

𝐾𝑉𝐴 𝑟𝑎𝑡𝑖𝑛𝑔 𝑋 𝑝𝑜𝑤𝑒𝑟 𝑓𝑎𝑐𝑡𝑜𝑟 + 𝑡𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠𝑠

Output =KVA rating X power factor

For maximum efficiency

Output = xscosφ

X = 𝑊1+𝑊2 +𝑊3

𝑊4


33

Total Loss=2x2W4

Maximum Efficiency =𝑜𝑢𝑡𝑝𝑢𝑡

𝑂𝑢𝑡𝑝𝑢𝑡 +𝑇𝑜𝑡𝑎𝑙 𝑙𝑜𝑠𝑠

Result: - Suitable test is conducted and

The efficiency of three phase alternator is at full load

Maximum Efficiency of three phase alternator is

EXP.NO. 6 DATE:

BRAKE TEST ON 3–Φ SQUIRREL CAGE INDUCTION MOTOR

AIM: To draw the performance characteristics of 3-phase squirrel cage induction motor by

conducting load test.

NAME PLATE DETAILS:

Parameters Induction Motor

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUS REQUIRED:

S.No Name of apparatus Type Range Qty.

1. Ammeter MI

2. Voltmeter MI


34

3. Wattmeter EDM

4. Tachometer digital

5. Connecting Wires

THEORY:

A 3-phase induction motor consists of stator and rotor with the other associated parts. In the

stator, a 3-phase winding is provided. The windings of the three phase are displaced in space

by 120º.A 3-phase current is fed to the 3-phase winding. These windings produce a resultant

magnetic flux and it rotates in space like a solid magnetic poles being rotated magnetically.

CIRCUIT DIAGRAM:

PROCEDURE:

1.Connections are given as per circuit diagram.

2.3-Ф induction motor is started with DOL starter.

3. If the pointer of one of the wattmeter readings reverses, interchange the current coil

terminals and

take the reading as negative.

4.The no load readings are taken.


35

5. The motor is loaded step by step till we get the rated current and the readings of the

voltmeter,

ammeter, wattmeters, spring balance are noted.

PRECAUTIONS:

1.TPST switch is kept open initially.

2.There must be no load when starting the load.

FORMULAE USED:

1) % slip= (Ns-N/Ns)*100

2) Input Power = (W1+W2)watts

3) Output Power = 2∏NT/60 watts

4) Torque = 9.81*(S1-S2)*R N-m

5) % efficiency = (o/p power/i/p power)* 100

OBSERVATIONS:

S.NO

Line

Voltage

volts

Input

Current

Amps

Wattmeter Reading

Spring Control

Speed

W1*4

watts

W2*2

watts

S1 S2

1

2

3

4

5

6

CALCULATIONS:

Speed

S1- S2

T

(S1-

S2)9.81

Out put

power

2𝜋NT/60

Input

power W1+ W2

Slip Ns − 𝑁

Ns

Power

factor 𝑖/𝑝

3𝑉𝐼

ɳ


36

GRAPHS:

1) Output Power vs Efficiency

2) Output Power vs Torque

3) Output Power vs Speed

4) Output Power vs %s


37

RESULT: Hence the load test on Squirrel cage Induction motor is performed and

performance characteristics are drawn.

EXP.NO. 7 DATE:

REGULATION OF 3–Φ ALTERNATOR BY SYNCHRONOUS IMPEDANCE

AND MMF METHODS

AIM:

To predetermine the regulation of 3-phase alternator by EMF and MMF methods and

also draw the vector diagrams.

NAME PLATE DETAILS:

Parameters DC Shunt Motor Alternator

Rated Power

Rated Voltage

Rated Current

Rated Speed

Rated field current



1 Ammeter MC


38

2 Ammeter MI

4 Voltmeter MI

5 Rheostat Wire

wound

6 Potential Divider Wire

wound


THEORY:

The regulation of a 3-phase alternator may be predetermined by conducting the Open

Circuit (OC) and the Sort Circuit (SC) tests. The methods employed for determination of

regulation are EMF or synchronous impedance method, MMF or Ampere Turns method and

the ZPF or Potier triangle method. In this experiment, the EMF and MMF methods are used.

The OC and SC graphs are plotted from the two tests. The synchronous impedance is found

from the OC test. The regulation is then determined at different power factors by calculations

using vector diagrams. The EMF method is also called pessimistic method as the value of

regulation obtained is much more than the actual value. The MMF method is also called

optimistic method as the value of regulation obtained is much less than the actual value. In

the MMF method the armature leakage reactance is treated as an additional armature reaction.

In both methods the OC and SC test data are utilized.

CIRCUIT DIAGRAM:


39

PROCEDURE: (FOR BOTH EMF AND MMF METHODS)

1. Note down the name plate details of the motor and alternator.

2. Connections are made as per the circuit diagram.

3. Switch ON the supply by closing the DPST switch.

4. Using the Three point starter, start the motor to run at the synchronous speed by

adjusting the motor field rheostat.

5. Conduct Open Circuit test by varying the potential divider for various values of field

current and tabulate the corresponding Open Circuit Voltage readings.

6. Conduct Short Circuit test by closing the TPST switch and adjust the potential divider

to set the rated armature current and tabulate the corresponding field current.

7. The Stator resistance per phase is determined by connecting any one phase stator

winding of the alternator as per the circuit diagram using MC voltmeter and ammeter

of suitable ranges.

PROCEDURE TO DRAW GRAPH FOR EMF METHOD:

1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS

Field current).

2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field

current)

3. From the graph find the open circuit voltage per phase (E1 (ph) for the rated short

circuit current (Isc).

4. By using respective formulae find the Zs, Xs, Eo and percentage regulation.

PROCEDURE TO DRAW GRAPH FOR MMF METHOD:


40

1. Draw the Open Circuit Characteristic curve (Generated Voltage per phase VS

Field current).

2. Draw the Short Circuit Characteristics curve (Short circuit current VS Field

current)

3. Draw the line OL to represent

PRECAUTIONS:

(i) The motor field rheostat should be kept in the minimum resistance position.

(ii) The alternator field potential divider should be kept in the minimum voltage

position.

(iii) Initially all switches are in open position.

FORMULAE:

1. Armature Resistance Ra = Ω

2. Synchronous Impedance Zs = O.C. voltage

S.C. current

3. Synchronous Reactance Xs = √ Zs2 – Ra

2

4. Open circuit voltage for lagging p.f = √(VcosΦ + IaRa)2 + (VsinΦ + IaXs)

2

5. Open circuit voltage for leading p.f. = √(VcosΦ + IaRa)2 + (VsinΦ – IaXs)

2

6. Open circuit voltage for unity p.f = √(V + IaRa)2 + ( IaXs)

2

7. Percentage regulation = (Eo – V)/V

TABULAR COLUMNS

OPEN CIRCUIT TEST:

S.No.

Field Current (If) Open Circuit Line

Voltage (VoL)

Open circuit Phase

Voltage (Voph)

Amps Volts Volts

1

2

3

4

5

6

7

8

9

10

11

SHORT CIRCUIT TEST:

S.No.

Field Current (If)

Short Circuit Current (120%

to 150% of rated current)

(ISC)

Amps Amps


41

1

MODEL GRAPH:

RESULT:

Thus the regulation of 3-phase alternator has been predetermined by the EMF and

MMF methods.


42

EXP.NO. 8 DATE:

V AND INVERTED V CURVESOF 3–Φ SYNCHRONOUS MOTOR

AIM To draw the V and inverted V curves of a 3 phase Synchronous Motor.

NAME PLATE DETAILS:

Parameters Synchronous Motor

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUS REQUIRED:

S.no Name of

Apparatus

Range Type Quantity


43

1 Ammeter MI

2 Voltmeter MI

3 Wattmeter EDM

4 Rheostat Wire Wound


6 Connecting

Wires

THEORY:

The variation of field current effects the power factor at which the synchronous motor

operates. For a syn motor, the armature current phasor is given by Ia=V-E where V is the

applied voltage .From the above equation it is clear that the magnitude and phase angle of

phasor Ia

depends upon the value of DC excitation. When the syn. Motor is operated at constant load

with variable field excitation, it is observed that:

a) When the excitation is low, the armature current is lag in nature & the magnitude is

comparatively high.

b) If the excitation is gradually increased, the magnitude of Ia is gradually decreasing and the

angle of lag is gradually reduced.

c) At one particular excitation, the magnitude of Ia corresponding to that load in minimum

and vector will be in phase with V vector.

d) If the excitation is further increased, the magnitude of Ia again gradually increased and Ia

,vector goes to leading state and the angle of load is also gradually increased.

CIRCUIT DIAGRAM:


44

PROCEDURE:

(1) Note down the name plate details of the motor.

(2) Connections are made as per the circuit diagram..

(3) Close the TPST switch.

(4) By adjusting the autotransformer from the minimum position to the maximum

position the rated supply is given to motor. The motor starts as an induction

motor.

(5) In order to give the excitation to the field for making it to run as the synchronous

motor, close the DPST switch.

(6) By varying the field rheostat note down the excitation current, armature current

and the power factor for various values of excitation.

(7) The same process has to be repeated for loaded condition.

(8) Later the motor is switched off and the graph is drawn.

PRECAUTION:

(1) The Potential barrier should be in maximum position.

(2) The motor should be started without load.

(3) Initially TPST switch is in open position.

OBSERVATION TABLE:


45

S.NO IF

Amps

V

Volts

Ia

Amps

W1

Watts

W2

Watts

W

W1+ W2

Watts

COSΦ=

W/( 𝟑 VL

IL)

1

2

3

4

5

6

7

Power Factor:

CosΦ=(W/ 3 VLIL)

Where IL= Ia+ IF

MODEL GRAPHS:


46

The graph is drawn for-

(1) Armature current Vs Excitation current.

(2) Power factor Vs Excitation current.

RESULT: The determination of V and inverted V curves of three phase synchronous motor

was obtained.

EXP.NO.09 DATE:


47

EQUIVALENT CIURCUIT AND PRE-DETERMINATION OF PERFORMANCE

CHARACTERISTICS OF 1Ф INDUCTION MOTOR

AIM:

To draw the performance characteristics of a single phase induction motor by

conducting the no-load and blocked rotor test.

NAME PLATE DETAILS:

Parameter 1Ф -Induction Motor

Rated Power

Rated Voltage

Rated Current

Rated Speed

APPARATUS REQUIRED:

S.No Name of

Apparatus

Range Type Qty.

1 Voltmeter MI

MI

2 Ammeter MI

MI

3 Wattmeter UPF EDM

LPF EDM

4 Connecting

wires

THEORY:

A 1-Ф induction motor consists of stator,rotor and other associated parts.In the rotor of a

single phase winding is provided.The windings of a 1- Ф winding(provided) are displaced in

space by 120º.A single phase current is fed to the windings so that a resultant rotating

magnetic flux is generated.The rotor starts rotating due to the induction effect produced due

to the relative velocity between the rotor winding and the rotating flux.

CIRCUIT DIAGRAM:


48

PROCEDURE:

NO LOAD TEST:

1. Connections are given as per the circuit diagram.

2. Precautions are observed and the motor is started at no load.

3. Autotransformer is varied to have a rated voltage applied.

BLOCKED ROTOR TEST:

1. Connections are given as per the circuit diagram.

2. Precautions are observed and motor is started on full load or blocked rotor position.

3. Autotransformer is varied to have rated current flowing in motor.

4. Meter readings are the noted.

PRECAUTIONS:


49

NO LOAD TEST:

Initially TPST Switch is kept open.

Autotransformer is kept at minimum potential position.

The machines must be started on no load.

BLOCKED ROTOR TEST:

Initially the TPST Switch is kept open.

Autotransformer is kept at minimum potential position.

The machine must be started at full load(blocked rotor).

Reff = 1.5*Rdc

FORMULAE:

NO LOAD TEST:

cos Ф = Wo/VoIo

Iw = Io cosФ

Im = Io sin Ф

Ro = Vo/Iw

Xo = Vo/Im

BLOCKED ROTOR TEST:

Zsc = Vsc/Isc Ω

Rsc = Wsc/Isc2 Ω

Xsc = √(Zsc2

– Rsc2) Ω

TABULAR COLUMNS

NO LOAD TEST:

S.No. Vo(volts) Io(amps) Wo(watts)

1

BLOCKED ROTOR TEST:


50

S.No. Vsc(volts) Isc(amps) Wsc(watts)

1

EQUALENT CIRCUIT:

RESULT: Thus the pre-determination of Equivalent circuit parameters and

efficiency of 1-phase induction motor was obtained as follows

EXP.NO.10 DATE:


51

SLIP TEST ON 3–Φ ALTERNATOR

AIM:To measure Direct Axis (Xd) and Quadeature Axis (Xq) synchronous reactance of

Synchronous machine by performing SLIP Test.

NAME PLATE DETAILS:

PARAMETERS DC Shunt Motor Alternator

Rated Power

Rated Voltage

Rated Current

Rated Speed

Rated field current

APPARATUS REQUIRED:

S.no Name of

Apparatus

Range Type Quantity

1 Ammeter MI

2 Voltmeter MI

3 Variac

4 Rheostat Wire Wound


6 Connecting

Wires

THEORY:

In a salient pole alternator, the reactance of magnetic circuit along is along its quad stator

axis. The alternator is driven by auxiliary prime mover at a speed slightly less than the

synchronous speed under these conditions. The armature current is when the armature current

mmf is in line with the field poles. The reactance by the magnetic field current is minimum.

The ratio of maximum voltage to minimum current gives the direct axis impedance and the

ratio of minimum voltage to maximum current gives the armature axis impedance.

The values of Xd & Xq are determined by conducting the slip-test. The syn. machine is

driven by a separate prime mover at a speed slightly different from synchronous speed. The

field winding is left open and positive sequence balanced voltages of reduced magnitude

(around 25% of the rated value) and of rated frequency and impressed across the armature

terminals. Here, the relative velocity b/w the field poles and the rotating armature mmf wave

is equal to the difference b/w syn. speed and the rotor speed i.e, the slip speed . When the

rotor is along the d-axis, then it has a position of min reluctance, min flux linkage and max

flux produced links with the winding.then Xd = (max. armature terminal voltage/ph) / (min.

armature current/ph)As the current is small then Vt

will be high as drop will be small.When the rotor is along q-axis, then it is max, then the flux

linkage would be max.Then The min flux produced links with winding. So max emf. Xq =

(min. armature terminal voltage/ph) / (max. armature current/ph)

CIRCUIT DIAGRAM:


52

PROCEDURE:


53

1. Note down the name plate details of motor and alternator.

2. Connections are made as per the circuit diagram.

3. Give the supply by closing the DPST switch.

4. Using the three point starter, start the motor to run at the synchronous speed by

varying the motor field rheostat at the same time check whether the alternator field

has been opened or not.

5. Apply 20% to 30% of the rated voltage to the armature of the alternator by adjusting

the autotransformer.

6. To obtain the slip and the maximum oscillation of pointers the speed is reduced

slightly lesser than the synchronous speed.

7. Maximum current, minimum current, maximum voltage and minimum voltage are

noted.

8. Find out the direct and quadrature axis impedances.

PRECAUTIONS:

1. The motor field rheostat should be kept in minimum.

2. The direction of the rotation due to prime mover and the alternator on the motor

should be the same.

3. Initially all the switches are kept open.

TABULAR COLUMNS

To find the Direct Axis and Quadrature axis impedances:

S.NO Vmax Vmin Imax Imin

1

OPEN CIRCUIT TEST:

S.No.

Field Current (If) Open Circuit Line

Voltage (VoL)

Open circuit Phase

Voltage (Voph)

Amps Volts Volts

1

SHORT CIRCUIT TEST:


54

S.No.

Field Current (If)

Short Circuit Current (120% to

150% of rated current) (ISC)

Amps Amps

1

FORMULAE USED:

1. Rac=1.6Rac Ω

2. Zd = Vmax/Imin Ω

3. Zq = Vmin/Imax Ω

4. Xd = √Zd2 – Rd

2 Ω

5. Xq = √Zq2 – Rd

2 Ω

6. Id = Ia sinФ amps

7. Iq = Ia cos Ф amps

8. %Reg = (Eo-V/V)*100

Where,

Zd = direct axis impedance in Ω

Zq = quadrate axis impedance in Ω

Xd = direct axis reactance in Ω

Xq = quadrate axis reactance in Ω

Id = direct axis current in amps

Ia = quadrate axis current in amps

RESULT: Hence by performing slip test we find the values of Xd= and Xq= .

ADDITIONAL EXPERIMENT NO:-1 DATE:


55

SCOTTCONNECTION

AIM : To convert three phase system to two phase system with the help of scott

Connection

NAME PLATE DETAILS:

Rated power

Rated voltage

Rated current

Frequency

APPARATURS REQUIRED: SL.NO Name of the Apparatus Type Range Quantity

1 Ammeter

2 Ammeter

3 Voltmeter

4 Voltmeter

5 Wattmeter

6 Wattmeter

7 Dimmerstat

THEORY :- Phase conversion from three to two phase is needed in special cases, such as in

supplying 2-phase electric arc furnaces.

The concept of 3/2-phase conversion follows from the voltage phasor diagram of

balanced 3-phase supply shown in Fig 1. If the point M midway VBC could be located , then

VAM leads VBC by 90o. A 2-phase supply could thus be obtained by means of transformers;

one connected across AM, called the teaser transformer and the other connected across the

lines B and C. since VAM= (3/2) VBC , the transformer primaries must have 3 N1/2 (teaser)

and N1 turns; this would mean equal voltage/turn in each transformer. A balanced 2-phase

supply could then be easily obtained by having both secondaries with equal number of turns,

N2. The point M is located midway on the primary of the transformer connected across the

lines B and C. The connection of two such transformers, known as the Scott connection, is


56

shown in Fig. 1(a), while the phasor diagram of the 2-phase supply on the secondary side is

shown in Fig. 1(c).

The neutral point on the 3-phase side, if required, could be located at the point N

which divides the primary winding of the tertiary in the ratio 1 : 2 (refer Fig.)

LOAD ANALYSIS:-

A

C B M

N

(b)

_

Va

_

Vb (c)

_

Ia

_

Ib

A

_

IA

B

_

Ic

_

Vb + _

N2 b1 b2 / Ib

C

_

IB

M N1 / 2 N1 / 2

_

IBC

_

IA / 2

_

IA / 2

+

_

_

Va N2

a1

a2

3 N1 / 2

N _

IA

Teaser Transformer

1(a)


57

If the secondary load currents are IA and IB , the currents can be easily found on

the 3-phase side fig.1(a).

_ _

IA = (2N2 / 3N1) x Ia = (2 Ia / 3) (for N1 / N2 = 1)

_ _ _

IBC = N2 / N1 Ib = Ib (for N1 / N2 = 1)

_ _ _

IB = IBC - IA / 2

_ _ _

Ic = - IBC - IA / 2

The corresponding phasor diagram for balanced secondary side load of unity power

factor is drawn in fig. (2) from which it is obvious that the currents drawn from the 3-

phase system are balanced and cophasal with the star voltages. The phasor diagram for the

case of an unbalanced 2-phase load is drawn in fig (3)

A

C B

IA

IBC

IA / 2 IB

IC

- IA / 2

- IBC

Vb

Ib

Ia Va

a

b

Fig.(3)

A

B C

IA = 23

IBC =1 - IBC

- IA / 2 - IA / 2 = 1 / 3

Ic IB = 1 + 1/ 3 = 2 / 3

Vb Ib 1

Va

Ia

1

Fig.(2)


58

PROCEDURE :

V

V

V

0 – 300

V,MI

0 – 300

V,MI

0 – 600

V,MI

0

0

41

5

24

0 Main

Transformer

2 KVA

415 /

240 V

50

%

0 0

24

0

Teaser

Transformer

2 KVA,415 / 240

86.6

%

V

0–600

V,MI

CIRCUIT DIAGRAM:

SCOTT CONNECTION

415V, 3-,

50Hz,

AC Supply

B

||

||

||

||

||

||

||

||

||

||

||

||

||

||

||

||

||

415V, 3-,

50Hz,

AC Supply

Y

R

T

P

S

T

10

A

10

A

10

A


59


(2) By using 3- auto transformer apply different voltages to the circuit.

(3) Note down the all the meter readings.

(4) Observe different meter readings.

TABULAR FORM :

S.NO 3 - SUPPLY 2 - SUPPLY

VRY in

volts

VYB

in volts

VBR

in volts VPh in volts VPh in volts VL in volts

RESULT:

ADDITIONAL EXPERIMENT NO:-2 DATE:


60

Parallel Operation Of Two Single Phase Transformers AIM:-

To operate the given two 2KVA, 230/110V single phase Transformers in parallel and stud y

the

load sharing between them when supplying resistive load .

NAME PLATE DETAILS:

1Φ - TRANSFORMERs

T/F T/F-1 T/F-2

HV side LV side HV side LV side

Rated power

Rated voltage

Rated current

Frequency



1 Ammeter MI

2 Ammeter MI

3 Voltmeter MI

4 Voltmeter MI



7 Dimmerstat

THEORY:


61

PROCEDURE :-

a) Make connections as for circuit diagram, keep the load switch and switch S open .

b) Switch on the mains , see the volt meter reading of V1 , if this reading is 460V(double

the secondary voltage of both the machines) then switch of and inter change the

connections of secondary of any transformer . if reads zero then the switch S can be

closed , this way the polarities can be checked since wrong polarity will short circuit

the transformers if operated in parallel .

c) Close switch S and then close the load switch.

d) For various values of load current , record terminal voltage ,current in two secondary’s

, power supply by the two transformers and the total power,(do not exceed 10 A for

total current)

e) Switch of load and switch of main.

f) Determine the equivalent reactance’s and resistance’s of both transformers referred

to HV winding by SC test


62

CAULATIONS :-For a given load current IL at an angle ф the current and power

supply by each

transformer can be found out by the following formula

IA= (IL)X(ZB)/(ZA+ZB)

IB = (IL)X(ZA)/(ZA+ZB)

If S is the load KVA, then the KVA shared by the transformers can be found out by

SA= (S)X(ZB)/(ZA+ZB)

SB = (S)X(ZA)/(ZA+ZB)

Check the result obtained with the Theoretical calculations .

RESULTS:-

a) With the help of phasor diagram verify if IA = IB= I.

b) Check if the load shared is proportional to the KVA capacities of the respective

transformers

c) From the results state if RA /XA =RB /XB

st semester laboratory manual of electrical machines...

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