Rctifi Machine-1 (1)lab manual

8/10/2019 Rctifi Machine-1 (1)lab manual

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LABORATORY MANUAL

ELECTRICAL MACHINES-I

ELECTRICAL & ELECTRONICS ENGINEERING

CENTURION INSTITUTE OF TECHNOLOGY

Name:

Branch:

Semester:

Section:

Regd. No.:


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PREFACEThis Laboratory book in Electrical MachinesI has been

revised in order to be up to date with Curriculum changes,

laboratory equipment upgrading and the latest circuit

simulation.

Every effort has been made to correct all the known

errors, but nobody is perfect, if you find any additional errors or

anything else you think is an error, Please contact the Dept. ofEEE

The Authors thanked all the staff members from the

department for their valuable Suggestion and contribution

The AuthorsDepartment of EEE


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OVERVIEW

Scope of Electrical & Electronics Engineering:

The Department of Electrical & Electronics Engineering of CIT is one among the

branches instituted in 2008. While retaining its strength in traditional areas of engineering, the

department grew with time, reflecting the needs of a changing society and established new areas

of teaching & research in electrical engineering.

The syllabus of the department has tremendously augmented with many advanced

courses with focus on the following areas: Network analysis & synthesis, machine analysis &

design; control engineering; Basics of analog & digital electronics circuits; microprocessor &

micro controllers; procedural & object-oriented languages; and in-depth coverage of power

systems. State of the art infrastructure has been established in order to promote a congenial

academic environment to impart quality education.

Sincere efforts have been made to implement the Decentralized Functioning in its letter

and spirit. Student sub-committees have been set up who work along with the Lab. In-Charge,

and staff attached to the laboratory towards up-keep and effective utilization of the assigned

laboratory. Through devolution of powers, the administration in the department has been

effectively made transparent.

Department Mission

To produce Electrical & Electronics Engineers with dynamic well rounded personalities

adaptable to ever increasing demands of emerging technologies involving analytical and

practical skills so as to serve the society.

Department Vision:

o To develop the department as an academic center of excellence in the discipline of

electrical engineering.

o To establish value based research and development activities so as to encourage active

participation with industry by staff and students to take on real-time problems of

industry and to provide feasible solutions.


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o To establish tie-ups with institutions of national and international repute and to foster

building up of a wide knowledge base to keep in tune with ever increasing demands of

technologies.

Short range Goals

To bring out skilled and disciplined graduates by imparting quality education in the

field of electrical engineering.

To recruit well-qualified and experienced faculty to enhance the quality of teaching.

Setting up of well-equipped laboratories.

Encouraging the faculty to update their knowledge through quality improvement

programmes.

To promote the use of computer based resources in teaching and training.

To organize faculty orientation programmes by arranging technical talks, conducting

workshops, seminars involving experts in the respective fields.

Words from H.O.D.

The Department of Electrical Engineering at CIT is recognized among the leading centers

of teaching and research in Electrical & Electronics Engineering in the state. In every

semester along with regular theory courses students have to take at least 8 laboratory courses

which instill confidence in the student to handle practical problems in the field of

engineering. After the fourth and sixth semesters, the students are sent for Industrial Training

to various national institutes, PSUs, industries and electric utilities all over India during the

summer vacation. This gives the students the exposure to work in the industrial environment.

The department is ready to provide the industry with another young dynamic lot of

engineers well equipped with the determination and the skill to excel in whatever they choose

to do.


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Syllabus

ELECTRICAL MACHINES-I (PCEE3101)THEORY

MODULE- I[16 hours]

1. DC GENERATORS:

Construction, working principle, Armature Windings (Simplex Lap and Simplex Wave), Methods

of Excitation, Expression for EMF Induced, Armature Reaction, Commutation, Interlopes,

Compensating Windings.

2. DC GENERATOR CHARACTERISTICS:

Characteristics for Separately Excited DC Generator (No-Load and Load), Conditions for Self

Excitation, Critical Resistance and Critical Speed, Characteristics for Self Excited DC Shunt

Generator (No-Load and Load), Voltage Regulation, Parallel Operation of DC Shunt Generators

and DC Series Generators.

MODULE- II

[17 hours]

3. DC MOTOR CHARACTERISTICS:

Characteristic for Speed-Armature Current, Torque-Armature Current and Speed-Torque of (i)

Separately Excited DC Motor, (ii) DC Shunt Motor, (iii) DC Series Motor, and (iv) DC Compound

Motor, Comparison between Different types of DC Motors and their Application.

4. DC MOTOR STARTING and PERFORMANCE CHARACTERISTICS :

Necessity of a Starter, Starting of DC Shunt, Series and Compound Motors, Precautions During

Starting of DC Series Motor, Speed Control of DC Shunt and Series Motors, Classification of

Losses, Efficiency Evaluation from Direct and Indirect Methods (i) Brake Test (Direct method), (ii)

Swinburnes Test (Indirect method), (iii) Regenerative/Hopkinsons Test (Indirect method).MODULE- III

[17 hours]

5. SINGLE PHASE TRANSFORMER:

Constructional Features, EMF Equation, Turns Ratio, Phasor Diagrams at No-Load and Load

Conditions, Equivalent Circuit, Determination of Parameters From Tests (Open Circuit Test and

Short Circuit Test, Back to Back test), Voltage Regulation, Losses and Efficiency, Auto

Transformers and their application.

6. THREE PHASE INDUCTION MACHINES:

Constructional Features of Squirrel Cage Rotor type and Slip Ring/Wound Rotor type of Induction

Motors, Principle of Operation, Concept of Slip, Slip Speed, Equivalent Circuit and Phasor

Diagram, No-Load and Blocked Rotor tests, Determination of Parameters, Slip~Torque

Characteristics Losses and Efficiency. Starting of Squirrel Cage Rotor type and Slip Ring/WoundRotor type of Induction Motors, Speed Control of Induction Motors, Cogging, Crawling and

Electrical Braking of Induction Motors Induction.


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LIST OF EXPERIMENTS TO BE PERFORMED:

PCEE3108 Electrical Machines-I Lab (0-0-3)

List of Experiment: (any ten)1. Determination of critical resistance & critical speed from no load test of a

DC Shunt generator.2. Plotting of external and internal characteristics of a DC shunt generator.3. Determination of efficiency of DC machine by direct loading.4. Determination of efficiency of DC machine by Swinburnes Test.5. Determination of Efficiency and Voltage Regulation by Open Circuit and

Short Circuit test on single phase transformer.6. Speed control of DC Motor by Ward-Leonard Method.7. Study of current, voltage & frequency of a 1-ph transformer & to calculate

voltage and current of the transformer using CRO.8. Polarity test and Parallel operation of two single phase transformers.9. Back to back test of a single phase transformer.10.Load characteristics of DC (i) self (ii) separately excited DC generator.11.Calculation of earth resistivity of industrial earthing.12. Separation of core losses of a DC machine.

Text Book:

1. Electrical MachinesD P Kothari and I J NagrathTata McGraw Hill.

Reference Book(s):

2. Electrical MachineryP S BimbhraKhanna Publishers.

3. Electrical MachinesP.K.Mukherjee & S.ChakravortiDhanpat Rai Publications

4. Electrical Machines-I. - B.L.Theraja- S.Chand Publications.


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BASICS OF EXPERIMENTATION

Doing each experimental exercise in a laboratory helps in deeper understanding of physical

concepts.vis-a-vis the theory taught. THE BASIC AIM IS TO EXPERIMENT A THEORY

AND ARRIVE AT VALUE BASED CONCLUSIONS. At the beginning of each experiment,

this manual provides guidelines to perform the experiments. Conducting experiments serve the

following purposes:

To be familiar with the basic components, measuring instruments and other

equipments.

To learn the techniques of measuring basic electrical and non electrical quantities.

To realize the limitations of accuracies of measuring instruments.

To physically verify Theorems/ Laws pertaining to a topic AND ASCERTAIN HOW

FAR THE RESULTS VARY FROM THE THEORITICAL VALUES.

To get training of technical report writing.

Before coming to the laboratory, a student should become familiar with the theoretical

background and the necessary circuit diagram for conducting the experiment. Merely making the

connections and taking a reading mechanically doesnt help in developing an understanding the

matter. The student must know the changes to be made to a parameter and observe the responses

to these changes.


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General Instructions and Precautions:

Safety rules

S FETY

is of paramount importance in theElectrical

Laboratories.Since you are going to work with equipments and machines operating at high voltages, such

as 220V DC supply, 230 V, 50 Hz, AC supply or 440 V, 50 Hz, 3-Phase AC supply, you should

take utmost care to avoid electric shock hazards. Furthermore, enough care should be taken so as

to get, meaningful results without damaging any equipment or instrument.

Therefore it is important to adhere the following general instructions and precautions.

o Never work alone in the laboratory.

o Always put on shoes with rubber soles so as to provide insulation from ground.

o Dont wear loose dress while working in the laboratory.

o Power should be switched of before changing any connection.

o Familiarize yourself with the first aid instructions for electrical shocks

o Keep away from moving parts.

o Use fuse wire or MCB (miniature circuit Breaker) of proper rating.

o Use suitable wires for different parts of the circuits.

o Take down complete specifications from the name plate of the machines and

equipments. This will enable you to decide the range of all instruments to be used.

o Switch ON the supply only after connection have been checked.

o Dont touch any live terminal, while the supply is ON.


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Power Supply Systems:Following power supply systems are available in the electrical engineering laboratories:

1. 230V, 50 Hz, Single Phase Supply: It has two wires- Phase/Line wire and Neutral wire.(Fig-1).

2. 400 V, 50 Hz, 3-Phase () AC supply: Normally it has four wires- three for phase/lineand one for Neutral (Fig-2).

3. 220V, DC supply: This may be obtained either from a DC generator or a rectifier. It has

two wirespositive (+) and Negative (-).

Variable Electricity Supply:

DC Supply: Variable DC supply can be obtained by using a suitable Rheostat (Variable

Resistance) as shown in the Fig-3.

AC supply:Variable AC supply can be obtained by using an auto-transformer with a variable

tap (also known as Variac orDimmer stat) as shown in the Fig-4. For 3-Phase () AC supply we

use a 3-Phase () Variac. (Fig-4)


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Common Instruments:

Following are the important instruments and equipments used in the laboratories for

measurement of an electrical quantity. It is important to select a proper instrument with proper

range.

1.Ammeters and Voltmeters:

The basic principle of operation of these two instruments is the same. An

ammeter is used for measuring current. It has low resistance and must be connected in

series with the circuit. A voltmeter is used for measuring voltage across two points of a

circuit. It has high resistance and must be connected across (in parallel) with the two points.

2. Wattmeter:

A wattmeter is an instrument that measures the power (both dc and ac) going to

an electrical load. It has two coils called current coil and potential (or pressure) coil. The

terminals of the current coil are marked as M and L; and those of the pressure coil as C and

V. The terminals M and C are joined together to make a common terminal. The current coil

is connected in series with the load and the pressure coil across the load as shown in Fig.-5.

Sometimes, the wattmeter can give negative reading. In such a case, the

connections of either the current coil or the pressure coil are to be reserved and the reading

is to be treated as negative.

3. Tachometer:

It is used for the measurement of rotating speed in rpm (revolutions per

minute) of a machine. The tapered shaft of the tachometer is inserted into the tapered hole

in the shaft of the machine. The reading of the tachometer is proportional to the speed of

rotation of its shaft. A tachometer can be either analog type or digital type.


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4.Rheostat:

It is a variable resistance made up of a closely wound wire of high resistivity

(such as nickel-chromium-iron alloy) over a circular insulating tube. These are available

both in single tube and double-tube configurations. A rheostat is specified in terms of its

resistance and the maximum current it can carry. Normally it is 1000, 1.2A and 100,

5A. Rheostats are used as variable resistances and potential dividers.

5.Loading devices:

Commonly used loading devices are (i) lamp bank and (ii) loading rheostats.

A lamp bank consist of a number of 230V lamps (100W, 60W, 40W etc) suitably connected

and controlled by switches to provide different loads. A loading rheostat consists of a

number of identical resistive elements, suitably connected in series, parallel and

combinations thereof.


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TROUBLE SHOOTING HINTS

1. Be Sure that the power is turned ON

2. Be sure the ground connections are common

3. Be sure the circuit you build is identical to your circuit diagram (Do a node by node check)

4. Be sure that the supply voltages are correct

5. Be sure that the equipment is set up correctly and you are measuring the correct parameters

6. If steps 1 through 5 are correct then you probably have used a component with the wrong

value or one that doesnt work. It is also possible that the equipment does not work

(although this is not probable). To find your problem you must trace through the voltages in

your circuit node by node and compare the signal you expect to have. Then if they are

different use your engineering judgment to decide what is causing the different or ask your

lab assistant

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

RECOVERED FROM THE INDIVIDUAL WHO HAS DAMAGED THE INSTRUMENT IN ANY

MANNER.


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DOS IN THE LAB

1. Maintain silence in the lab.

2. Before entering the lab come prepared with the theory of the concernedexperiment.

3. Keep your other belongings in the allocated place.

4. Always come to the lab with lab manual and lab notebook.

5. Draw the items and deposit the same before leaving the room.

6. Before doing the experiment be confident about what you are doing.

7. After making the connection get it checked thoroughly by the concernedstaff (Faculty / Lab Assistant)

8. After completion of experiment return the entire instrument to the concernedstaff.

DONTS IN THE LAB

1. Dont fiddle with the control knobs / systems.

2. Dont play with electrical points.

3. Dont switch on any system without bring checked by the concerned.

4. Dont copy the reading from other.

5. Dont use pliers as hammer. i.e., Use the right tool at right place.


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TABLE OF CONTENTS

EXPT.NO. DATE NAME OF THE EXPERIMENTS

PAGENO.

TEACHERSSIGNATURE

REMAR

1.

2.

3

4.

5.

6.

7.

8.

9.


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10.

11.

12.


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LABORATORY REPORT


DEPARTMENT OF ELECTRICAL & ELECTRONIC ENGINEERING

CENTURION INSTITUTE OF TECHNOLOGY, BHUBANESWAR

EXPERIMENT NO. - 1


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AIM OF THE EXPERIMENT: - Determination of critical resistance and critical speed from

no load test of a DC shunt generator.

MACHINE SPECIFICATION:Motor: Volts: Ampere: Power: RPM:

Generator: Volts: Ampere: Power: RPM:

APPARATUS REQUIRED:

Sl No Apparatus name Specification Type Quantity

1 Ammeter MC (0-1)A 1

2 Tachometer Digital (0-9999) rpm 1

3 Connecting Wires 1.5 sq.mm copper As per required

CIRCUIT DIAGRAM:


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THEORY:

Conditions for Voltage Build-Up of a Shunt Generator

The necessary conditions for voltage build-up in a shunt generator are:

There must be some residual magnetism in generator poles.

The connections of the field winding should be such that the field current strengthens the

residual magnetism.

The resistance of the field circuit should be less than the critical resistance. In other

words, the speed of the generator should be higher than the critical speed.

To obtain no-load characteristics, the generator should be driven at its rated speed by a prime-

mover and the load circuit should be open circuited. Hence the no-load characteristic is otherwise

called open circuit characteristics (OCC). It is the relation between terminal voltages (E g) with

respect to field current (If).

To Plot OCC:

The induced emf in DC generators is given by the equation volts. State P, Z, A areconstants the above equation are written as Eg= KN. If the speed of the generator also maintained

constant then Eg= K but the flux is directly proportional to thecurrent. Hence Eg=K If. From the

above equation it is clear that the induced emf is directly propositional to the field current when

speed maintained constant. The plot between the induced emf and the field current is known as open

circuit characteristics of the DC generator.The induced emf when the field current is zero is known as residual voltage. This emf is due to

the presence of a small amount of flux detained in the field poles of the generator called residual

flux. Once the OCC is obtained parameters such as critical field resistance & critical speed can be

determined.

To Determine Critical Resistance (Rc):

Critical resistance is defined as the resistance of the field circuit which will cause a self-

excited generator just to build up its EMF at a specified speed. It can be obtained from OCC by

drawing a straight line passing through the origin & tangent to the initial straight line portion of

OCC. The slope of this line gives the critical field resistance.

It should be noted that shunt generator will build up only if the field circuit resistance is less

than the critical field resistance and above that generator will fail to excite.

To Determine Critical Speed (Nc):

The critical speed of a shunt generator is the minimum speed below which it fails to excite.

Speed Critical resistance


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To find critical speed, taking any convenient point(C) on ecitation axis and erect a

perpendicular so as to cut Rsh and Rc lines at points B and A respectively. Then,

where N is the motor running speed(rated speed)

PROCEDURE:

1. Do the connections as per the circuit diagram given in the figure.

2. Keeping the motor field rheostat in its minimum position, generator field rheostat in its

maximum position and the starter in its off position, the main supply is switched ON.

3. The motor is started using the three point starter by slowly and carefully moving the

starter handle from its OFF to ON position.

4. The motor to brought to its rated speed by adjusting its rheostat and checked with the

help of a tachometer.

5. Initially the generator is driven at its rated speed. The voltmeter reading is noted down

corresponding to zero field current which is the emf reading due to residual flux.

6. Now the generator field Rheostat is varied in step and at each step the field current (If)

and the corresponding induced EMF (Eg) are recorded in the tabular column.

OBSERVATION TABLE:

SL NO Field Current If Induced EMF Eg


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GRAPHS: Plot the graphs with induced emf (Eg) in the Y axis & field current(If) in the X axis

which gives the OCC of a shunt generator.

CALCULATION:

1.Draw a straight line passing through the origin and tangent to the initial straight line portion of

OCC. Find the slope of this line. It gives the critical field resistance.

2.Draw Rsh (shunt field resistance) line on the same graph.

3.To find critical speed, taking any convenient point(C) on excitation (If) axis and erect a

perpendicular so as to cut Rsh and Rc lines at points B and A respectively. Then,

Where N is the motor running speed (rated speed)

PRECAUTION:

1. All connectionshould be made right and tight.

2. Any live terminal should not be touched while supply is on.

3. The voltmeter, ammeter and wattmeter should be carefully chosen so that their ranges are

more than maximum value to be measured.

4. Motor should not exceed rated speed.

CONCLUSION:


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SPACE FOR GRAPH


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SPACE FOR ROUGH


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LABORATORY REPORT




EXPERIMENT NO. - 2


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AIM OF THE EXPERIMENT: - Plotting of external and internal characteristics of a DC

shunt generator.

MACHINE SPECIFICATION:-

Motor: Volts: Ampere: Power: RPM:

Generator: Volts: Ampere: Power: RPM:

APPARTUS REQUIRED:-

S.No. Apparatus Range Type Quantity

1 Ammeter (0-1)A MC 1

2 Tachometer (0-1500) rpm Digital 1

3 Connecting Wires 1.5sq.mm. CopperAs per

required

CIRCUIT DIAGRAM:


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THEORY:

The speed of a DC machine operated as a generated is fixed by the prime mover. For

general purpose operation, the prime mover is equipped with a speed governor so that the speed

of the generator is practically constant. Under such condition, the generator performance deals

primarily with the relation between excitation, terminal voltage and load. These relations can be

best exhibited graphically by means of curves known as generator characteristics. These

characteristics show at a glance the behavior of the generator under differential load condition.

The following are the three most characteristics of a DC generator:

i) No-load Saturation Curve(Eo/If):

It is also called open circuit characteristics or magnetic characteristics. It gives the

relation between the no-load generated EMF in armature (E0) and the field or exciting current

(If). This characteristic is same for separatelyexcited and selfexcited generators.

ii) Internal Characteristics(Eg/IL):It practically gives the relation between the EMF (Eg) actually induced in the armature

conductors (after considering the demagnetizing effect of armature reaction) and the armature

current IL. It is also known as total characteristics.

When the generator is loaded, flux per pole is reduced due to armature reaction.

Therefore, e.m.f Eggenerator on load is less than the emf generated at no-load. As a result, the

internal characteristic drops down slightly as shown in graph.

iii) External Characteristics (Vt/IL):

It shows the relation between the terminal voltage VT and the load current IL. It is also

called performance characteristics or sometimes called voltage regulation curve.It gives the relation between terminal voltage Vtand load current IL.

V = E- IaRa

= E(IL + Ish)Ra

Therefore, external characteristics curve will lie below the internal characteristics curve

by an equal amount to drop in armature circuit [i.e., (Ia+Ish)Ra] as shown in graph.


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PROCEDURE:

There are two methods for characterizing a DC generator:

i. With load

ii. Without load

For open circuit:

1. Connections are made as per the circuit diagram.

2. After checking minimum position of motor field rheostat, maximum position of generator

field rheostat, DPST switch is closed and starting resistance(starter) is gradually

removed.

3. By adjusting the field rheostat, the motor is brought to rated speed.

4. Voltmeter and ammeter readings are taken when the SPST switch is kept open.

5. After closing the SPST switch, by varying the generator field rheostat, voltmeter and

ammeter readings are taken.

6. After bringing the generator rheostat to maximum position, field rheostat of motor tominimum position, SPST switch is opened and

7. DPST switch is opened.

For load test:


2. After checking minimum position of DC shunt motor field rheostat and maximum

position of DC shunt generator field rheostat, DPST switch is closed and starting

resistance is gradually removed.

3. Under no load condition, Ammeter and Voltmeter readings are noted, after bringing the

voltage to rated voltage by adjusting the field rheostat of generator.4. Load is varied gradually and for each load, voltmeter and ammeter readings are noted.

5. Then the generator is unloaded and the field rheostat of DC shunt generator is brought to

maximum position and the field rheostat of

6. DC shunt motor to minimum position, DPST switch is opened.

For Without load test:

The external characteristic of a shunt generator can be obtained directly from its no-load

saturation curve. The following two cases are taken into account:

i) Neglecting armature reactionii) With armature reaction

Neglecting the Armature Reaction:

1. From the given data plot the OCC as shown in figure 4.26.

2. A shunt field resistance line (OS) is drawn that meets at the point A.


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3. A horizontal line intersecting the y-axis at B is drawn from the point A. OB is the

maximum no-load or open circuit voltage.

4. A point L is taken on OCC and an ordinate LMN is drawn which intersects the field

resistance line and X-axis at M and N respectively. LN, MN and LM represent the

generated emf, the terminal voltage and voltage drop in armature respectively.

5. From points L and M horizontal lines are drawn that cut the vertical axis at points D and

E respectively.

6. An armature resistance line OC is drawn.

7. A line EF parallel to line OC cutting line LD extended at F is drawn from point E. The

point F is lying on the internal characteristic.

8. Other points can be obtained and internal characteristic drawn through these points.

9. A vertical line is drawn from the point F which intersects the extended line ME at the

point G and X-axis at a point T. The point G lies on the curve representing the relation

between armature current and terminal voltage because FG=LM=CT.

10.TU is the shunt field current and it is equal to ON. OU represents yhe load currentcorresponding to armature current represented by OT and terminal voltage OE.

11.A vertical line intersecting line EG at H is drawn from U. The point H lies on the

external characteristic.

12.The other points can be obtained similarly. The curve through these points gives external

characteristic.

WITH ARMATURE REACTION:Here the voltage drop due to armature reaction, in addition to volage drop due to

armature resistance,is considered.

A right angle triangle lmn is drawn such that ln and mn represent the voltage drop in

armature and shunt field current respectively. The triangle lmn is known as the drop reactiontriangle. All the processes in section 4.31 are repeated with the following modifications to draw

the internal and external characteristic.

1. A point L is taken on the OCC and a line LM parallel to lm is drawn and the triangle

LMN is completed. The vertical lines are drawn from the points L and M which cuts

X-axis at points N and M respectively.LNMMLN and ON represent the generated

emf,terminal voltage drop in armature resistance and the shunt field current to induce

an emf represented by LN respectively. NM represents the increase in shunt field

current to counteract the damagnetising effect.

2. TU is the shunt field current which is equal to ON and OU represents the load current

corresponding to the armature current represented by OT and terminal voltage MM.


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TABULATION:

Speed= __________ rpm

SL.NO. Load

current(IL)

Terminal

Voltage(Vt)

Field

Current(If)

Average value of armature resistance (Ra)=__________

Sl. No. Ia=IL+If E= Vt + IaRa


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GRAPH:

i. Plot the OCC curve(Eg vs If) from the tabulation

ii. Plot the external characterstics or load characterstics(VTvs IL) from the table.

iii. Plot the internal characterstics or total characterstics(E vs IL) from the table

MODEL GRAPH:

CONCLUSION:


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SPACE FOR GRAPH


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LABORATORY REPORT




EXPERIMENT NO. - 3


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AIM OF THE EXPERIMENT:

Speed control of DC Motor by Ward-Leonard Method.

.

MACHINE SPECIFICATION:

DC shunt machine: -

Voltage: Current: Speed: Power:

APPARATUS REQUIRED:


1 Rheostat 200 ohm, 3A 1-Tube 02

3 Ammeter (0-1) A MC 01

4 Voltmeter (0-300) V MC 015 Tachometer (0-9999) rpm Digital 01

6 Connecting wires 2.5 sq.mm PVC LS

CIRCUIT DIAGRAM:


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THEORY:

Adjustable voltage is obtained from the system shown in above diagram. The armature of the

shunt motor M (whose speed is to be controlled) is connected directly to a d.c. generator G driven by a

constant-speed a.c. motor A. The field of the shunt motor is supplied from a constant-voltage exciter E.

The field of the generator G is also supplied from the exciter E. The voltage of the generator G can be

varied by means of its field regulator. By reversing the field current of generator G by controller FC, thevoltage applied to the motor may be reversed. Sometimes, a field regulator is included in the field circuit

of shunt motor M for additional speed adjustment. With this method, the motor may be operated at any

speed upto its maximum speed.

PROCEDURE:

1) Do the connections as per the circuit diagram given in the figure. Keep both the rheostats at

their minimum resistance positions.

2) Start the DC shunt motor with the help of three-point starter. Increase the resistance of the

rheostat connected in the field circuit. Do not change the armature circuit rheostat at all.

Observe the increase in motor speed. Record five sets of readings in table 1.Then switch off

DC supply and bring the field circuit rheostat to minimum.

3) Start the DC shunt motor with the help of three-point starter. Increase the resistance of the

rheostat connected in the armature circuit. Do not change the field circuit rheostat at all.

Observe the decrease in motor speed. Record five sets of readings in table 2. Then switch off

DC supply and bring the armature circuit rheostat to minimum.

OBSERVATION TABLE:

Table1:1

Sl No. Field Current(If) Speed(rpm)

Table 2:

Sl No. Armature Voltage Speed(rpm)


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GRAPHS: Plot the graphs for speed verses field current and speed verses armature voltage.


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PRECAUTIONS:

1) Field Rheostat should be kept in the minimum resistance position at the time of starting

and stopping the motor.

2) Armature Rheostat should be kept in the maximum resistance position at the time of

starting and stopping the motor.

3) Do not start the motor keeping the field circuit open.

4) Connection should be tight.

5) Parallax error should be avoided

CONCLUSION:


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SPACE FOR GRAPH


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SPACE FOR ROUGH


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LABORATORY REPORT




EXPERIMENT NO. - 4


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AIM OF THE EXPERIMENT: - Determination of efficiency of DC machine by

Swinburnes Test.


Volts: Ampere: Power: RPM:

APPARTUS REQUIRED:-



2 Voltmeter (0-300)V MC 1

3 Rheostat 1250, 0.8A Wire Wound 1


5 Connecting Wires 2.5sq.mm. Copper Few

CIRCUIT DIAGRAM:


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Then, Armature current, Ia= IIsh, For motor

= I + Ish, For generator

Advantages:

1) It is convenient and economical method of testing of DC machines since power required to test a large

machine is very small.

2) The efficiency of the machine can be predetermined at any load. Since stray losses are known

Disadvantages:

1) This test cannot be performed with dc series motors.

2) This test is only applicable to those machines in which flux and speed remainconstant.

3) As the test is performed on no load it is impossible to know whether at full load commutation would be

satisfactory and the temperature raise would be within specified limits or not.

4) No account is taken for change in iron losses form no load to full load on account of distribution of flux due

to armature reaction. On full load the flux distribution is very much affected due to armature reaction and is

some case to an extent that iron losses become 1.5 times of iron losses at no load..

PROCEDURE

a. Make all the connections are as per the circuit diagram.

b. Keep the field rheostat in minimum resistance position.

c. Excite the motor with 220V, DC supply by closing the DPST switch and start the motor by moving the

handle of 3-point starter from OFF to ON position.

d. By adjusting the rheostats in motor armature and field bring the speed of the motor to its rated value. Note

down the readings of Ammeter and Voltmeter at no load conditione. The necessary calculation to find efficiency of machine as motor & generator at any given value of

armature current is done.

TO FIND ARMATURE RESISTANCE(Ra):

1) Connect the circuit per the circuit diagram

2) Keep the rheostat in maximum position.

3) Now excite the motor terminals by 30V supply by closing DPST switch. By varying the rheostat & motor

down the readings of Ammeter and voltmeter


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TABULATION:

Motor on NO-LOAD

Vo

VOLTS

Io

Amps

If

Amps

Ia = IOIf

Amps

Speed (N)

RPM

To find Armature Resistance (Ra)

SL.NO Armature Voltage(V)

Volts

Armature Current(I)

Amps

Armature Resistance(Ra)

Ohms

AVG.=


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PREDETERMINATION OF LOSSES AND EFFICEINCY AT DIFFERENT

LOADS:

(i) As a Motor:

SL.

NO

Load

VoltageVL

Volts

Load

CurrentIL

Amps

Armature

CurrentIa

Amps

Copper

lossesI2 aRa

Watts

Total

lossesWi + Wc

Watts

Input

PowerVL IL

Watts

Output

Power =I/P -losses

Watts

Efficiency

%

(ii) As a Generator:

SL.NO LoadVoltage

VL

Volts

LoadCurrent

IL

Amps

ArmatureCurrent

Ia

Amps

Copperlosses

I2 aRa

Watts

Totallosses

Wi+

Wc

Watts

OutputPower

VLIL

Watts

InputPower

O/p+losses

Watts

Efficiency

%


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GRAPH :Constant losses vs No load voltage

PRECAUTIONS:Before switching ON the supply it is ensured that:

1. The field rheostat is kept in minimum resistance position.2. The armature rheostat is be kept in maximum resistance position.

CONCLUSION:


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SPACE FOR GRAPH


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SPACE FOR ROUGH


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LABORATORY REPORT




EXPERIMENT NO. - 5


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AIM OF THE EXPERIMENT: -

Determination of efficiency of three phase induction motor by performing by load

test



APPARTUS REQUIRED:-

SL NO. APPARATUS SPECIFICATION TYPE QUANTITY

01 Voltmeter (0-600)V MI 01

02 Ammeter (0-10)A MI 01

03 Wattmeter (0-600)V, (0-10)A LPF Dynamometer 02

04 3-phase Auto-

Transformer

415/(0-470)V,10A 01

05 Brake Drum

Arrangement

- - -

06 Tachometer (0-9999)RPM Digital 01

07 Connecting wire 3/22 SWG PVC As required

CIRCUIT DIAGRAM:-

BRAKE TEST ON THREE PHASE SQUIRREL CAGE INDUCTION MOTOR:


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PROCEDURE:-

1. The connections are made as per the circuit diagram.

2. Power supply is obtained from the control panel and he TPST switch is closed.

4. Rated voltage of 3-phase induction motor, is applied by adjusting the autotransformer.5. The initial readings (at no-load) of ammeter, voltmeter and wattmeter are noted.

6. By increasing the load step by step, the reading of ammeter, voltmeter and wattmeter.

Also note down the reading of load on each step.

7. Step1 to 6 is repeated till the ammeter shows the rated current of 3-phase induction

motor.

8. Decrease the load, bring auto-transformer to its minimum voltage position.

9. Switch off the supply.

10. Calculate the torque and slip from formula, and draw the graph (torque in Y-axis and slip

in X-axis).

Note: If any of the wattmeter readings shows negative on no load or light loads, switch of the

supply & interchange the terminals of pressure coils/current coils (not both) of that wattmeter.

Now, again starting the motor (follow above procedure for starting), take readings.


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OBSERVATION:-

SL.

NO

V

(volt)

I

(A)

Speed

(rpm)

Spring Balance Torque =

[(S1S2) *9.81 * R]

N-m

I/P=

(V*IL)Or

(W1 +

W2)

watt

O/P=

2 NT60

(watt)

Efficiency,

%

=

%Slip,

S1

(Kg)

S2

(Kg)

CALCULATION: FORMULA:

Torque, T = (S1S2) * 9.81 *R (Nm) Input power, Pi= (W1+ W2) Watt

Output power, Po=

Watt Efficiency, = * 100

Slip = (NsN) / Ns *100 Radius =


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PRECAUTION:

1. TPST switch should be at open position.

2. 3-phase autotransformer should be at minimum voltage position.3. There should be no-load at the time of starting (Loosen the belt on the brake drum).

4. Brake drum should be filled with water.

CONCLUSION:


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SPACE FOR ROUGH


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55

LABORATORY REPORT




EXPERIMENT NO. -6


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AIM OF THE EXPERIMENT: -

Determination of Efficiency and Voltage Regulation by Open Circuit and Short Circuit

test on single phase transformer.


Voltage Ratio:

Current:

Power:

Frequency:

APPARATUS REQUIRED:-

SL

NO.

APPARATUS SPECIFICATION TYPE QUANTITY

01 Voltmeter (0-150-300)V MI 02



04 Wattmeter (0-230)V/0-10A Dynamometer 01

05 Variac 0-270V,10A - 01

06 Connecting wires 2.5 sq.mm PVC As required


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CIRCUIT DIAGRAM:-

CIRCUIT FOR OPEN CIRCUIT TEST

CIRCUIT FOR SHORT CIRCUIT TEST


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THEORY:

Open-circuit or No-load Test:

This test is performed to determine core or iron loss, W 0and parameters R0 and X0. This

test is helpful in determination of magnetizing component Imand iron less component Iw and so

no-load resistance R0being given as V1/Iw and no-load reactance X0given as V1/Im.

In this test secondary (usually high voltage) winding is left open, all metering instruments

(ammeter, voltmeter and wattmeter) are connected on primary side and normal rated voltage is

applied to the primary (low voltage) winding, as illustrated above in circuit diagram.

Iron loss, Pi= Input power on no-load = W0watts (wattmeter reading)

No-load current =I0amperes (ammeter reading)

Applied voltage = V0 (Voltmeter reading)

No-Load P.F. cos 0= W0/ V0I0

Angle of lag, 0= cos

-1

Wo/V0IoIw = I0cos 0and Im = I0sin 0

R0= V1/ Iw and X0=V1/ Im

Caution: Since no load current I0 is very small, therefore, pressure coils of wattmeter and the

voltmeter should be connected such that the current taken by them should not flow through the

current taken by them should not flow through the current coil of the watt meter.

2. Short-circuit or Impedance Test:

This test is performed to determine the full-load copper loss and equivalent resistance

and reactance referred to secondary side.

In this test, the terminals of the secondary winding(usually the low voltage) are short

circuited, all meters (ammeter, voltmeter and wattmeter) are connected on primary side and a

low voltage, usually 5 to 10 % of normal rated primary voltage at normal frequency is applied to

the primary, as shown in fig above. The applied voltage to the primary, say V sis gradually

increased till the ammeter indicates the full load current of the side in which it is connected. The

reading Wsof the wattmeter gives total copper loss (iron losses being negligible due to very low

applied voltage resulting in very small flux linking with the core) at full load. Let the ammeter

reading be Is.

Full load copper loss, Psc = I2

sR1= Wsc

Equivalent resistance referred to primary, R1 = Wsc/I2

s

Equivalent impedance referred to primary = Z1= Vs/Is

Equivalent impedance referred to primary, X1= [(Z'1)2(R'1)

2']

1/2


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Voltage regulationis the measure of how well a power transformer can maintain constant

secondary voltage given a constant primary voltage and wide variance in load current. The lower

the percentage (closer to zero), the more stable the secondary voltage and the better

the regulation it will provide.

PROCEDURE:

OPEN CIRCUIT TEST:


2. After checking the minimum position of Autotransformer.

3. Auto transformer variac is adjusted get the rated primary voltage.

4. Voltmeter, Ammeter and Wattmeter readings on primary side are noted.

5. Auto transformer is again brought to minimum position and DPST switch is

opened.

SHORT CIRCUIT TEST:


2. After checking the minimum position of Autotransformer.

3. Auto transformer variac is adjusted get the rated primary current.

4. Voltmeter, Ammeter and Wattmeter readings on primary side are noted.

5. Auto transformer is again brought to minimum position and DPST switch is

opened.

CALCULATION:

Open Circuit Test:

Sl.

No.

Voltage

(V0)

Current

(I0)

Power

(Po)

Power factor,

Cos=


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Short Circuit Test:

Sl.

No.

Voltage

(Vsc)

Current

(Isc)

Power

(Psc)

Power factor,

Cos=

CALCULATION:IW= I0 COS 0

I= I0Sin0

R0=V1/IW

X0 = V1/I

Z01 = VSC/ISC

RO1=PSC/I2

SC

X01=

EFFICIENCIES:

1) At full load and at rated power factor

( )

2) for half full load and rated PF

( )


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SPACE FOR GRAPH


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63

MODEL GRAPHS:

Efficie

nc

%

Output power (Watts)

Power factor

% lagging

% leading


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LABORATORY REPORT




EXPERIMENT NO. - 7


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AIM OF THE EXPERIMENT: - Polarity test and Parallel operation of two single phase

transformers.


Voltage Ratio: Current: Power: Frequency:

APPARATUS REQUIRED:-

SL

NO.


01 Voltmeter (0-125-250)V MI 02




CIRCUIT DIAGRAM:-


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Circuit diagram for subtractive polarity

Circuit diagram for additive polarity


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THEORY:-

Two transformers are said to be connected in parallel if the primary

windings are connected to supply bus bars & secondary windings are connected to the load bus

bars shown in the figure. While connecting two or more transformers in parallel, following

conditions must be satisfied:1. The voltage ratio must be the same.

2. The per unit impedance of each machine on its own base must be the same.

3. The polarity must be the same, so that there is no circulating current between the

transformers.

4. The phase sequence must be the same and no phase difference must exist between thevoltages of the two transformers.

By parallel operation we mean two or more transformers are connected to the same supply bus

bars on the primary side and to a common bus bar/load on the secondary side. Such requirement

is frequently encountered in practice. The reasons that necessitate parallel operation are as

follows:

1. Non-availability of a single large transformer to meet the total load requirement.

2. The power demand might have increased over a time necessitating augmentation of the

capacity. More transformers connected in parallel will then be pressed into service.

3. To ensure improved reliability. Even if one of the transformers gets into a fault or is

taken out for maintenance/repair the load can continued to be serviced.

4. To reduce the spare capacity. If many smaller size transformers are used one machine can

be used as spare. If only one large machine is feeding the load, a spare of similar rating

has to be available. The problem of spares becomes more acute with fewer machines in

service at a location.5. When transportation problems limit installation of large transformers at site, it may be

easier to transport smaller ones to site and work them in parallel.

PROCEDURE:

a) Polarity test:

- connect the circuit as shown in the diagram.

- Switch on the single phase a.c. supply.

- Record the voltages V1, V2 and V3. In case V3 V1 polarity

is additive.

- Switch off the a.c. supply

b) Turn Ratio Test:

- Connect the circuit as shown in the diagram.

- Switch on the a.c. supply.


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- Record voltage V1 across primary and V2 across various tappings of secondary.

- If V1>V2 then transformer is step down.

- If V2> V1 then transformer is step up.

- Switch off a.c. supply.

C) Parallel Operation :

a. connect the circuit as shown in the diagram.

b. Note down the readings of all ammeters and voltmeters for given load.

c. Repeat the above test for different values of load.

OBSERVATIONS:

Subtractive-Polarity

Sl No V1 V2 V3= V2

-V1

Additive Polarity

Sl No V1 V2 V3= V2

+V1

Turns Ratio Test:

S.NO. V1 V2 Turns Ratio

(V1/V2)


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TABULATION:-

SL NO. READING OF

AMMETER A1

IN AMP

READING OF

AMMETER

A2IN AMP

READING OF

AMMETER

A3IN AMP

A1+A2 PERCENTAGE

OF ERROR

01

02

03

04

05

06

07

08

09

10

PRECAUTION:-

Polarity/turns ratio must be checked.

Connection should be right & tight.

Voltmeter & ammeter should be carefully chosen so that their ranges are more than

maximum value to be measured.

Supply should be switched on after ensuring correctness of connection.

CONCLUSION:-


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SPACE FOR ROUGH


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LABORATORY REPORT




EXPERIMENT NO. - 8


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AIM OF THE EXPERIMENT: - Determination of parameters of 3- induction motor no load

test & Blocked Rotor Test.


Volts:

Ampere:

Power:

RPM:

Frequency:

APPARTUS REQUIRED:

SL

NO.






05 Wattmeter (0-600)V, (0-10)A LPF Dynamometer 02

06 3-phase Auto-

Transformer

415/(0-470)V,10A - 01

07 Brake Drum

Arrangement

- - -

08 Connecting wire 3/22 SWG PVC As required


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Procedure:

No-load test:

1. Connect the circuit as shown in the diagram.

2. The variac should be at zero voltage and motor should be unloaded.

3. Switch on the three phase a.c. supply.

4. Start the motor at reduced voltage and slowly increase the supply voltage using auto

transformer up to rated voltage.

5. Observe the direction of rotation and to reverse the direction of rotation change the phase

sequence.

6. Take the readings of all the meters.

7. Switch off

8. the supply.

Block Rotor test:

1. Block the rotor by mechanical load.

2. Slowly increase the voltage to allow the full rating current to flow.

3. Take the readings of all the meters and calculate the parameters using formulae.



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OBSERVATION:

No-load test:

SL

NO.

VOLTMETER

READING VO

(in volt)

AMMETER

READING IO

(in amp)

WATTMETER READING (in watts)

W1 W2 Total Power(W1+W2)

Block Rotor test:

SL

NO.

VOLTMETER

READING VO

(in volt)

AMMETER

READING IO

(in amp)

WATTMETER READING (in watts)

W1 W2 Total Power

(W1+W2)

CALCULATION:For No-Load:

VL= input line voltage

P = Total Power

I0 = input line current

VP= input phase voltage

= VLI0

I0 Amps and I0 AmpsRc =

and X=


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Blocked Rotor Test / Short Circuit Test:

Psc = total power input during this test (P)

Isc = Line Current on short circuit (I)

Vsc = line voltage on short circuit (V)

Psc = [where = circuit power factor]Equivalent Resistance of the rotor refer to stator (R01) =

Equivalent impedance of the rotor refer to stator (Z01) =

Equivalent reactance of the rotor refer to stator (X01) = Precaution:

1. All connectionshould be made right and tight.

2. Any live terminal should not be touched while supply is on.

3. The voltmeter, ammeter and wattmeter should be carefully chosen so that their ranges are

more than maximum value to be measured.

4. Motor should exceed rated speed.

Conclusion:


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SPACE FOR ROUGH


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LABORATORY REPORT




EXPERIMENT NO.9


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THEORY:-

Induction motor is a machine which converts AC electrical energy into mechanical

energy. In this motor the rotor does not receive electric power by conduction but by induction in

exactly as the secondary of 2winding transformer receives its power from the secondary. Thatis why such motors are known as rotating transformer. When you give three phase supply to the

three phase stator winding then it is called as three phase induction motor. The effect of applying

load on the speed, slip, stator current, power factor, efficiency and torque are discussed below:

EFFECT ON SPEED:When the induction motor is on no load the speed is slightly below the synchronous

speed. The current due to induced emf in the rotor is responsible for torque production requiredat no-load, as the load is increased the rotor speed is slightly reduced. The emf induced in

the rotor and hence the current increases to produce higher torque required until the torque is

equal to the torque required by the load on the motor.

EFFECT ON SLIP:Synchronous speed depends upon of frequency stator supply voltage and number of poles

for which that motor winding is made. Therefore if poles and frequency are constant,

synchronous speed is constant. Thus with increase in load on the motor, rotor speed decreases,slip will increase. %slip = (NsN /Ns) *100

EFFECT ON STATOR CURRENT:Current drawn by the stator is determined by two factors. One component is the

magnetizing current required to maintain the rotating field. The second component produces a

field which is equal and opposites to that formed by the rotor currents. The rotor current

increases with loads, the stator current will also therefore increases with load. Power factor of aninduction motor on no load is very low because of the high value of magnetizing current. With

load the power factor increases because the power component of the current is increased.

EFFECT ON TORQUE:The torque will increases with increase in loads, with increase in output.


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PROCEDURE:-

1. The connections are made as per the circuit diagram.

2. Power supply is obtained from the control panel and he TPST switch is closed.

4. Rated voltage of 3-phase induction motor, is applied by adjusting the autotransformer.5. The initial readings (at no-load) of ammeter, voltmeter and wattmeter are noted.

6. By increasing the load step by step, the reading of ammeter, voltmeter and wattmeter.

Also note down the reading of load on each step.

7. Step1 to 6 is repeated till the ammeter shows the rated current of 3-phase induction

motor.

8. Decrease the load, bring auto-transformer to its minimum voltage position.


10. Calculate the torque and slip from formula, and draw the graph (torque in Y-axis and slip

in X-axis).

Note: If any of the wattmeter readings shows negative on no load or light loads, switch of the

supply & interchange the terminals of pressure coils/current coils (not both) of that wattmeter.

Now, again starting the motor (follow above procedure for starting), take readings.


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OBSERVATION:-

SL.NO V

(volt)

I

(A)

Speed

(rpm)


[(S1

S2

) *

9.81 * R]

N-m

I/P=

(V*IL

)

Or

(W1 + W2)

watt

O/P=

2 NT60

(watt)

Efficiency,

%=

%Slip,

S1

(Kg)

S2

(Kg)

CALCULATION: FORMULA:

Torque, T = (S1S2) * 9.81 *R (Nm) Input power, Pi= (W1+ W2) Watt

Output power, Po=

Watt Efficiency, = * 100

Slip = (NsN) / Ns *100 Radius =


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PRECAUTION:

1. TPST switch should be at open position.

2. 3-phase autotransformer should be at minimum voltage position.

3. There should be no-load at the time of starting (Loosen the belt on the brake drum).

4. Brake drum should be filled with water.

CONCLUSION:


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SPACE FOR GRAPH


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SPACE FOR ROUGH


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LABORATORY REPORT




EXPERIMENT NO.10


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AIM OF THE EXPERIMENT: - Determination of Torque-Speed Characteristics of D.C.

Shunt motor.



APPARTUS REQUIRED:-



2 Voltmeter (0-300)V MC 1

3 Rheostat Wire Wound 1


5 Connecting Wires 2.5sq.mm. Copper Few

CIRCUIT DIAGRAM:

THEORY:


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89

The shunt motor has a definite no load speed hence it does not run away when load is

suddenly thrown off provided the field circuit remains closed. The drop in speed from no-load to

full-load is small hence this motor is usual referred to a constant speed motor. The efficiency

curve is usually of the same shape for all electric motors and generators. The shape of efficiency

curve and the point of maximum efficiency can be very considerable by the designer, though it is

advantageous to have an efficiency curve which is fairly flat. So that there is little change in

efficiency between load and 25% overload and to have the maximum efficiency as near to the

full load as possible. From the curves it is observed that is certain value of current is required

even when output is zero. The motor input under no-load conditions goes to meet the various

losses, occurring within the machine. As compared to other motors a shunt motor is said to have

a lowest starting torque. But this should not be taken off mean that is shunt motor is incapable of

starting heavy load. Actually it means that series and compound motor as capable of starting

heavy load with les excess of current inputs over normal values then the shunt motor and the

consequently the depreciation on the motor will be relatively less.

Speed (N) of a DC shunt motor can be expressed as

The motor when connected across constant voltage supply draws constant field current. The flux

which is proportional to the field current is thus constant. When the motor is loaded, armaturecurrent (Ia) increases with the increase in load causing an increase in armature drop (I aRa).

Generally, the armature resistance Ra is very small and hence the drop IaRa is quite small

compared to the applied voltage (V). This causes quite small drop in the speed on loading.

If the speed of the shunt motor is plotted against armature current, the characteristic will beobtained as shown in figure.

The torque developed is proportional to the product of flux and armature current IaT Ia

As is constant, T Ia


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TABULATION:

SL.N

O.

V

(volt)

I

(A)

Speed

(rpm)


[(S1

S2

) *

9.81 * R]

N-m

I/P=

(V*IL

)

watts

O/P=

2 NT60

(watts)

Efficiency,

%=

S1

(Kg)

S2

(Kg)

FORMULAE:

Torque T = (S1- S2) x R x 9.81 Nm Radius of the Brake drum, R = cm.Input Power Pi= VI Watts Output power, Po=

Watt

Efficiency, = * 100


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SPACE FOR GRAPH


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SPACE FOR ROUGH


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94

LABORATORY REPORT




EXPERIMENT NO. - 11


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AIM OF THE EXPERIMENT: Back to Back test on two single phase transformers.

MACHINE SPECIFICATIONS:

Voltage Ratio: Current: Power: Frequency:

APPARATUS REQUIRED:

Sl. No. Name Specificatons Type Quantity

1 Voltmeter (0-150-230) MI 2

2 Ammeter (0-1) MI 1

3 Ammeter (0-5) MI 1

4 Wattmeter (0-230)V, (0-5)A MI 2

5 Variac (0-270)V, 5A - 26 Connecting Wires 2.5 sq.mm PVC As Reqd.

CIRCUIT DIAGRAM:


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THEORY:

Though the efficiency and regulation of the transformer can be

determined from open-circuit and short-circuit tests accurately but for determination of

temperature rise it is necessary that the transformer be put on full load for a number of

hours. Transformers of smaller output can be loaded artificially by means of water

loads or lamp loads but it may be very difficult to arrange suitable loads for loading

transformers of large rating. Further there is tremendous wastage of electrical energy. In

Sumpners test the power required from the supply is that necessary for supplying

the iron and copper losses of both transformers. For this test two similar transformers

are required. The circuit diagram for performing Sumpners test is shown in the above figure.

The p r i mar y wi nd i ngs ( us ua l l y l ow vo l t age wi nd i ngs ) o f t he t wo

transformers are connected in parallel across a single phase supply with a

Voltmeter V1, Ammeter A1 and Wattmeter W1 in the circuit, as shown in the above figure.

The supply voltage V1 must be equ al t o th e ra ted vol tag e o f th e pr ima ry

wi nd i ngs . The s econdar y wi nd i ngs o f t he t r ans f o r mer s a r e connec t ed

t oge t he r s o t ha t t he i r po t en t i a l s a r e i n oppos i t i on t o eac h o t he r . Ther e f o r e

t he r e w i l l be no- c i r cu l a t i ng cu r r en t i n t he l oop f o r med by t he s econdar i e s

b ec aus e t h e i r i nd uced EMFs a re equa l a nd i n o pp os i t io n . Ther e i s an

aux i l i a r y l ow vo l t age t r ans f o r mer ( 1 - phas e va r i ac ) wh i ch can be ad j us t ed

t o g i ve a va r i ab l e vo l t age and henc e cu r r en t i n t he s econdar y l oop c i r cu i t .

A Voltmeter V2, Ammeter A2 and Wattmeter W2 are connected in secondary circuit.

OPERATION:

The secondary of the transformers are in phase opposition. With switch S1 closed and

Switch S2 open. There will be no circulating current (I2=0) in the secondary loop circuit. It isbecause the induced EMFs in the secondary are equal and in opposition. This situation is just like

an open circuit test. Therefore, the current drawn from the supply is 2Iowhere Io is the noload

current of each transformer. The reading of wattmeter W1 will be equal to the core losses of the

two transformers.

W1= core losses of the two transformers

Now Switch S2 is also closed and output voltage of the variac is adjusted till full load

current I2 flows in the secondary loop circuit. The full load secondary current will cause full-load

current I1(= KI2) in the primary circuit. The primary current I1 circulates in the primary winding

only and will not pass through W1. Note that full load currents are flowing through the primary

and secondary windings. Therefore reading of wattmeter W2will be equal to the full load copperlosses of the two transformers.

W2= full load copper losses of the two transformers


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Advantages:1. The power required to carry out the test is small.2. The transformers are tested under full-load conditions.3. The iron losses and full load copper losses are measured simultaneously.4. The secondary current I2can be adjusted to any current value. Therefore we can find

the copper loss at full load or at any other load.5. The temperature rise of the transformers can be noted.

PROCEDURE:1 . Connect as per the c i r cui t d iagram.2 . C l o s e t h e D P S T s w i t c h ( S 1 ) . Adjust the variac of the auto transformer

connected to transformer 1 to get the rated voltage.

3. Note down the read ing of ammeter , vol tmeter & wattmeter of tr ansformer1.4. Close the SPST switch if the voltmeter connected across the SPST switch

reads zero. If not the interchange the terminals of second transformer secondary to get

zero reading at SPST switch.

5. Adjust the variac of the auto transformer connected to transformer 2 to get therated current. Note down the reading of ammeter, voltmeter & wattmeter oftransformer2. While doing so, the values shown by V1, I1 and W1 should not deviate

from their earlier readings.6. Bring the auto transformer variac to zero position & switch off the suppl y.

TABULATION:

Primary side:

SL.No. Voltmeter(V1) Ammeter(A1) Wattmeter(W1)

Secondary side:

SL.No. Voltmeter(V2) Ammeter(A2) Wattmeter(W2)


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CALCULATION:

Core losses Wi=W1/2 Watts

Copper losses, Wc=W2/2*X2(Watts)

Where, X=percentage of Load

Total losses=Wc+WiWatts

Output power=KVA*100*X*p.f Watts

Input power=Output power + losses Watts

Efficiency=Output/Input*100


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SPACE FOR GRAPH


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SPACE FOR ROUGH


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LABORATORY REPORT




EXPERIMENT NO. - 12


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AIM OF THE EXPERIMENT:

Separation of losses of dc motor.


Voltage: Current: Power: RPM:

APPARATUS REQUIRED:




3 Ammeter (0-1/2) A MC 01

4 Ammeter (0-5/10) A MC 01

5 Voltmeter (0-300) V MC 016 Voltmeter (0-5) V MC 01



CIRCUIT DIAGRAM:


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THEORY:

In a DC motor, the no load input power supplies for the following losses:

1. Constant loss consisting of the iron losses or core loss and the mechanical loss due tofriction and wind age.

2. Armature copper loss and field copper loss (usually negligible).

In this experiment, the no load test is conducted on a DC motor in order to obtain the constant

losses. The mechanical loss is separated from the constant losses and hence the iron losses aredetermined. The constant losses are calculated as follows:-

Constant losses = No load inputArmature Cu loss (I2

aRa)i.e. Wc = V0I0Ia2 Ra

The mechanical loss Wmis found from the graph.

Hence the core losses or iron losses Wi = WcWm

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- load4. 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).

9. Stop the motor10.Measure the armature resistance by voltmeter-ammeter method using the circuit diagram

as shown in Fig.

11.Tabulate the readings.


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TABULATION:

Sl.

No.

No Load

Voltage

(Vo)

Volts

No

load

current

(Io)

Amps

No load

Input

Power

Wo=

VoIo

Watts

Field

Current

If

Amps

Armature

Current

Ia= Io - If

Amps

Armature

Cu Loss

I2

aRa

Watts

Constant

loss

Wc=

WoI2

aRa

Watts

Iron

loss

Wi =

Wc

Wm

Watts

CALCULATION:

No load input power Wo = VoIo Watts

Armature current Ia = IoIf Amps

Armature Copper loss = I2aRaWatts

Constant losses Wc = VoIoIa2Ra Watts

Mechanical loss = Wm(from graph) Watts

(friction and windage)

Core losses or Iron losses Wi = WcWm Watts

PRECAUTIONS:

1) Field Rheostat should be kept in the minimum resistance position at the time of starting

and stopping the motor.

2) Armature Rheostat should be kept in the maximum resistance position at the time of

starting and stopping the motor.

3) Do not start the motor keeping the field circuit open.


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SPACE FOR ROUGH


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Centurion University of Technology and Management

CUTM/EXAM/EX-008

Application for Compensatory Lab Classes

Name of the student:Regd. No.: Branch:Section:College_ID:

Date and laboratory for which remained absent

SL

NO

LABRORORY DATE EXP NOSIGNATURE OFCONCERNED

TEACHER WITHREMARKS

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Rctifi Machine-1 (1)lab manual

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