electrical machines- i laboratory manual...the electrical machines-i lab evaluation can be broadly...

POTTI SRIRAMULU CHALAVADI MALLIKHARJUNARAO COLLEGE OF ENGINEERING & TECHNOLOGY

(Affiliated to JNTU, Kakinada & Approved by AICTE New Delhi) KOTTHA PETA, VIJAYAWADA- 520001.

Department of Electrical and Electronics Engineering

**********************************************************

ELECTRICAL MACHINES-I

LABORATORY MANUAL

II B.Tech II Semester

Name:……………………………………………………......

RollNumber:……………………………………………....

Department of Electrical & Electronics Engineering

CERTIFICATE

This is to certify that this book is a bonafide manual practical work done in the Electrical Machines-1 Laboratory in ........semester of………year during the year….......

Name :-……………………………..

Roll.No :-……………………………

Branch :-…………………………….

Signature of the Staff member

PROGRAM OUTCOMES

PO.I: An ability to apply knowledge of mathematics, science, and engineering.

PO.II: An ability in design and conduct experiments as well as analyze and interpret

data.

PO.III: An ability in design an integrated system and its various components and

processes, within desired needs,

PO.IV: An ability to function effectively individually and on teams, including diverse and

multi-disciplinary to accomplish a common goal.

PO.V: An ability to identify, evaluate and solve engineering problems.

PO.VI: An understanding of the responsibility of engineers to practice in professional and

ethical manner at all times.

PO.VII: An ability to communicate effectively using oral, written and graphic forms.

PO.VIII: The broad education necessary to understand the potential impact of engineering

Solutions.

PO.IX: An understanding to the need for up to date engineering tools and other

knowledge acquired through lifelong learning.

PO.X: Knowledge of contemporary issues related to engineering.

PO.XI: An ability to use modern engineering tools, skills and design techniques necessary

for the practice of engineering.

PO.XII: An understanding of engineering and management principles and apply these to

one’s own work, as a member and leader in a team, to manage projects.

PROGRAM EDUCATIONAL OBJECTIVES

PEO.I: Excel in chosen career and /or higher education

PEO.II: Exhibit professionalism, ethical attitude, communication skills, team work and

adapt to current trends by engaging in lifelong learning

PEO.III: Demonstrate technical competence in solving engineering problems that are

economically feasible and socially acceptable

COURSE OBJECTIVES

To plot the magnetizing characteristics of DC shunt generator and understand the

mechanism of self-excitation.

To control the speed of the DC motors.

Determine and predetermine the performance of DC machines.

To predetermine the efficiency and regulation of transformers and assess their

performance.

COURSE OUTCOMES

To determine and predetermine the performance of DC machines and Transformers.

To control the speed of DC motor.

To achieve three phase to two phase transformation.

ACKNOWLEDGEMENT

It is one of life’s simple pleasures to say thank you for all the help that one has extended

their support. I wish to acknowledge and appreciate EEE Faculty for their sincere efforts made

towards developing the Power Electronics Lab manual. I wish to thank students for their

suggestions which are considered while preparing the lab manuals.

I am extremely indebted to Sri. Dr. K. Nageswara Rao, Principal and Sri. Y. Rajendra

babu, HOD of Electrical and Electronics Engineering, PSCMRCET for their valuable inputs and

sincere support to complete the work.

Specifically, I am grateful to the Management for their constant advocacy and

incitement.

Finally, I would again like to thank the entire faculty in the Department and those people

who directly or indirectly helped in successful completion of this work.

V. PRAVEEN

V.MATTHEW

EEE Department

DEPARTMENT OF ELECTRICAL & ELECTRONICS ENGINEERING

2017-2018

EVALUATION PATTERN

FOR ELECTRICAL MACHINES-I LABORATORY

The Electrical Machines-I lab evaluation can be broadly classified as per the contents Internal Assessment: 25 Marks 1. Two internals will be conducted for laboratory assessment. 2. Day-to-day work in the laboratory shall be evaluated for 15 marks. 3.Internal examination for practical shall be evaluated for 10 marks conducted by the

concerned laboratory teacher. End Examination Assessment: 50 Marks 1. The end examination conducted for 50 marks with duration of 3 hours. 2. The end examination shall be conducted with external examiner and laboratory teacher.

The external examiner shall be appointed from the cluster of colleges as decided by the

University examination branch.

LIST OF EXPERIMENTS

S.NO DATE NAME OF THE EXPERIMENT PAGE NO REMARKS SIGN

1 MAGNETIZATION CHARACTERISTICS OF DC

SHUNT GENERATOR. DETERMINATION OF

CRITICAL FIELD RESISTANCE AND CRITICAL

SPEED.

2 BRAKE TEST ON DC SHUNT MOTOR.

DETERMINATION OF PERFORMANCE

CURVES.

3 SWINBURNE’S TEST AND

PREDETERMINATION OF EFFICIENCIES AS

GENERATOR AND MOTOR

4 HOPKINSON’S TEST ON DC SHUNT

MACHINES. PREDETERMINATION OF

EFFICIENCY.

5 SPEED CONTROL OF DC SHUNT MOTOR BY

FIELD AND ARMATURE CONTROL

6 O.C. & S.C. TESTS ON SINGLE PHASE

TRANSFORMER

7 SUMPNER’S TEST ON A PAIR OF SINGLE

PHASE TRANSFORMERS

8 SCOTT CONNECTION OF TRANSFORMERS

9 PARALLEL OPERATION OF SINGLE PHASE

TRANSFORMER

10 SEPARATION OF LOSSES IN A DC SHUNT

MOTOR

CYCLE-1

1. MAGNETIZATION CHARACTERISTICS OF DC SHUNT GENERATOR.

DETERMINATION OF CRITICAL FIELD RESISTANCE AND CRITICAL

SPEED.

2. BRAKE TEST ON DC SHUNT MOTOR. DETERMINATION OF

PERFORMANCE CURVES.

3. SWINBURNE’S TEST AND PREDETERMINATION OF EFFICIENCIES AS

GENERATOR AND MOTOR.

4. HOPKINSON’S TEST ON DC SHUNT MACHINES. PREDETERMINATION OF

EFFICIENCY.

5. SPEED CONTROL OF DC SHUNT MOTOR BY FIELD AND ARMATURE

CONTROL

CYCLE-2

6. O.C. & S.C. TESTS ON SINGLE PHASE TRANSFORMER

7. SUMPNER’S TEST ON A PAIR OF SINGLE PHASE TRANSFORMERS

8. SCOTT CONNECTION OF TRANSFORMERS

9. PARALLEL OPERATION OF SINGLE PHASE TRANSFORMERS

10. SEPARATION OF CORE LOSSES OF A SINGLE PHASE TRANSFORMER

SAFETY RULES

1. Do not touch any terminal or switch when it is live.

2. Keep away from all the moving parts as far as possible.

3. Wearing of shoes with rubber soles is desirable.

4. Do not use loose garments, while working in the laboratory.

5. Use sufficient long connecting leads, rather than joining two or three small

ones.

6. The circuit should be de-energized, while changing any connection.

7. In case of emergency or fire, switch OFF the master switch on the main panel

board.

8. Do not open or close switches or fuse slowly hesitatingly, do it quickly.

9. Do not disconnect plug by pulling a flexible cable when the switch is ON.

10. Do not throw water on live electrical equipment in case of fire, use sand

instead.

11. Familiarize yourself with the shock-chart instructions.

GENERAL PRECAUTIONS

While working in electrical machine laboratory, following general precautions must be

observed.

1. Note down the complete details given on the name plate of the particular machine. Based

on this information and the aim of the experiment, decide the proper range for all the

instruments (ammeter, voltmeter, wattmeter, rheostat etc.) to be used for the experiment.

Special care should be taken to see that the value of current, voltage, speed etc. is not

exceeded beyond the permissible limit specified on the name-plate of the machine.

2. All the connections, made as per the circuit diagram of a particular experiment should be

tight. Do not allow any loose connections.

3. Use suitable wire for connecting different parts of the circuit. For example, thin wire

should be used for connecting the voltmeters and pressure coil of wattmeter, because

current is negligible. Thick wires of sufficient cross-section should be used for the current

carrying circuits.

4. When a motor is started never apply full voltage suddenly. Increase the voltage gradually

and bring it to the rated value.

5. While loading a particular machine, switch ON the load gradually and similarly switch

OFF gradually.

6. Keep all the meters used for the experiment in their proper position.

7. Switch ON the supply, only after getting the circuit checked by the in-charge guiding the

experiment.

8. Never touch any live terminals, while the experiment is being conducted.

For better conduction of the experiment, following information is quite useful.

SUPPLY SYSTEMS

A) D.C. Supply: 220V D.C

Fig.1 Shows the supply side of a D.C. circuit

Normally 220volts D.C. Supply is available on the panel board of a table, where

experimentation is to be carried out. This supply is fed to a given circuit through a switch and

fuses provided on the panel board of the table. Switch provided for this purpose is generally

double pole, single throw knife switch, normally designated as “DPST Switch”. Fuse provided is

as per the current rating of the given circuit or machine.

B) A.C.SUPPLY: Single Phase, 230V, 50Hz & Three Phase, 400V, 50Hz

Fig.2. Shows the supply side of an A.C. System feeding to alternating current circuit.

Single

phase, 230V,

50Hz, and 3-

phase, 400V, 50Hz, A.C. Supply is normally available on the panel board of a table in the

laboratory. Similar to the D.C. Supply, the supply is fed to an A.C. circuit through a proper

“DPST Switch” or “TPST Switch” (Triple Pole Single Throw) knife switch and fuses of proper

rating.

L2

To D.C

Circuit

DPST

Knife

Switch

+

-

220V D.C.

Supply

Fuse

Fig.1. D.C.Supply System

DPST

Knife

Switc

h

220V D.C.

Supply

L

N

To A.C

Circuit

Fig.2. A.C.Supply System

Fuse

INSTRUMENTS AND THEIR SELECTION

The instruments commonly used for various experiments are; ammeters, voltmeters and

watt meters of indicating type. These instruments indicate the magnitude of a quantity being

measured on a gradated scale. The moving system of such instruments is fitted with a pointer,

which moves over the calibrated scale to indicate the reading. Measuring instruments should not

alter the circuit conditions, when these are connected in a particular circuit for measuring a

certain quantity. These instruments should draw minimum possible power for their operation.

AMMETER AND VOLTMETER

Ammeters are used for the measurement of current in electrical circuits, such as these are

connected in series with the circuit. The voltage drop across the terminals of the ammeter, while

connected in series with the circuit should be as low as possible, so that the power consumption

of the meter is small. Hence the resistance of the current coil of the ammeter should be very low.

Voltmeters are used for measuring the potential difference across any two points of the

circuit. These are connected in parallel with the circuit for the measurement of voltage. The

voltmeter should draw a very small current, when connected in a circuit, so that its power

consumption is small. Hence the resistance of the voltmeter should be very high.

Ammeters and voltmeters generally used in machine laboratory are of two types

i) Moving Coil ii) Moving Iron.

MOVING COIL AMMETER AND VOLTMETER

Permanent magnet moving coil ammeter and voltmeter are used for measurement of

current and voltage respectively in a D.C. circuit, giving most accurate results. In these

instruments, deflecting torque or deflection of the moving system is directly proportional to the

current. Hence the scale of these instruments is uniformly calibrated, thus giving more accuracy

in measurement.

Normally moving coil ammeters and voltmeters are available in dual range. For example,

1/2A, 5/10A, 10/20A, 15/30A and 75/150V, 150/300V, 300/600V etc.

RHEOSTAT:

Variable resistances are commonly used for control purposes in machine laboratory.

When the resistance of the circuit can be varied without breaking the circuit, the device is termed

as rheostat. These are specified by the current which can be safely carried by them and the

resistance of its element (maximum value obtainable).

For example: 300Ω, 1.7A; 300Ω, 2A; 200Ω, 1.7A; 200Ω, 2A; 100Ω, 2A etc.

In experimentation, these are used in two modes, i) Variable Resistance ii) Potential Divider.

Rheostat as Variable Resistance:

The following fig. shows a rheostat used as a variable resistance in a circuit.

The resistance included in the circuit is zero, when the slider of the rheostat is moved to

the terminal “A"; and it will be in maximum when the slider is brought to the terminal “B”. Thus

any resistance value between zero and its maximum can be adjusted just by moving the slider on

the rheostat.

Rheostat as Potential Divider:

The use of rheostat as potential divider has been shown in the following fig.

Rheostat As Potential Divider

Fixed 220V

D.C. Supply

Variable D.C.

Supply A

B

C

L1+

L2-

Current

Limiting

Resistance

Rheostat As Variable Resistance

Fixed 220V

D.C. Supply

B

A

C

L1+

L2-

R

Variable

Resistance

A constant D.C. Voltage of 220V is applied between the terminals “A" and “B” of the

rheostat. When the slider of the rheostat is moved to "A", the output voltage is zero, where as it

would be maximum, when the slider is moved to “B”. Thus any value of D.C. voltage between

zero to 220V can be obtained from this circuit.

FUSES

Fuse is the short metal piece inserted in the circuit, which melts when current exceeds its

rated value, thus breaks the circuit.

The fuse wire is used for the protection of the equipment and the meters provided in the

circuit. Fuse is the weakest point in the circuit. So proper fuse wire is to be used, otherwise it

serves no purpose. It is the simplest and cheapest protection.

We should not make the fuse as the strongest point, always proper fuse wire is to be used

as per the current rating of the circuit.

Fuse rating is the current which the fuse element can normally carry without overheating

or melting.

Fusing current is the minimum current at which the fuse element melts and thus

disconnects the circuit.

Available Fuse Wires:

SWG Current Rating in

Amperes

Approximate Fusing

Current in Amperes

40 1.5 2.5

39 2.5 4.0

35 5.0 8.0

29 10.0 16.0

25 15.0 25.0

GENERAL INSTRUCTIONS FOR CONNECTING THE CIRCUIT

When an experiment is to be conducted in an electrical laboratory, circuit diagram

concerning to the experiment must be drawn with full understanding. The rating of various

instruments needed must be ascertained from the aim of the experiment and the rating of the

equipment under test. The circuit diagram should be drawn based on the aim of the experiment.

The circuit diagram for any experiment may be split up in to two sub circuits i.e. a

series circuit and a parallel circuit. Current in the series circuit is as per the loading condition of

the machine or equipment where as current in parallel circuit is negligible. Thus thick wire must

be used for connecting a series circuit, which may consist of an ammeter, current coil of

wattmeter, a rheostat and the load, all connected in series. Flexible wires should be used for

connecting a parallel circuit which may consist of voltmeter and pressure coil of wattmeter.

To start the connections of any given circuit diagram, first complete the connections of

the series circuit, including all necessary instruments and connect it to the proper supply system

through a switch(DPST/TPST)and the fuses of proper rating. Check the connection again before

proceeding further. Next start the connections of the parallel circuit using flexible wires.

Recheck the complete circuit again and satisfy yourself about the correctness of the connections.

Then only approach your guide and after his approval, proceed with the experiment.

REPORT WRITING

Proper writing of a concise and complete report on the experiment conducted is of

extreme importance. Following general pattern may be adopted for writing the report on various

laboratory experiments.

1. Aim / Objective of the experiment - Stating clearly the list of the tests performed and

result desired

2. List of apparatus - Give complete name-plate details of the machine, list of auxiliary

equipment, such as ammeters, voltmeters etc. along with their type and range.

3. Circuit Diagram – Draw complete diagram of connections along with various instruments

with their type and range marked.

4. Theory – Give the theoretical background, mathematical expressions etc. regarding the

particular experiment.

5. Procedure – Should be given step wise and in proper sequence.

6. Observations – Should be given in a tabular form.

7. Calculations – Better to give in a separate table along with sample calculations.

8. Performance Curves – Form an important part of the report. Should be drawn on a suitable

scale. Normally the dependent variable is plotted along the ordinate, where as independent

variable along the abscissa. Free hand smooth curves should be drawn, giving due

weightage to various points.

9. Precautions – Mention important precautions taken during experimentation.

10. Result – Give the result obtained by conducting the experiment as aimed.

11. Discussion – Give summary of the results, conclusion and the comparison with the

expected theoretical results.

12. Questions – Well selected questions would be suggested on each experiment. Students are

expected to answer these in the report.

STUDY OF DC MACHINE PARTS WITH FUNCTIONS & MEASUREMENT OF

ARMATURE AND SHUNT FIELD RESISTANCE

Learning Objectives:

To identify the various parts of DC machine

To understand the functions of individual parts

To determine the armature resistance

To determine the shunt field resistance

Aim : A) To study the mechanical details and note the functions of different parts of

a DC machine

B) To measure the armature and shunt field resistance of a DC machine.

PARTS OF A DC MACHINE:

The DC machine consists of a stationary part consisting of (a) Yoke (b) Field pole

(c) Field windings (d) Brushes (e) Inter poles (f) End covers The rotating part

comprises (g) Armature core (h) Armature windings (i) Commutator (j) Shaft

Functions of Different parts:

(1).Yoke: The yoke provides a low reluctance path for the pole flux and carries half of it

(Φ/2). It also provides mechanical support to the whole machine. Cast iron is used

for small machines and fabricated steel is used for the yoke of large DC machines.

As the flux is stationary, the yoke need not be laminated. Incase Dc motor is to be

operated through power electronic devices; the yoke is laminated to reduce eddy

current losses.

(2). Field Poles: Field poles consists of pole core and pole shoe. The pole core is made

from cast steel but pole shoe is made from their laminations. The pole core

and shoe are made of laminations in some cases.

(3). Field Winding: The filed winding is provided on the pole core and is excited by DC

current to produce flux Φ.

(4). Inter Poles: These are fixed to the yoke in between the poles. The winding on the inter

poles is of few turns and is connected in series with the armature

windings. Its purpose is to ensure good commutation.

(5). Brushes: Brushes are housed in box type holder attached to the stator end cover or yoke.

The small spring keeps the brushes pressed on to the commutator surface. The

brushes are made of carbon. Copper and graphite brushes are used for low

voltage, high current DC machines. The brushes maintain contact between the

stationary external circuit and the rotating armature winding through the

commutator.

(6). Armature Core: It is built with thin laminations (0.35 to 0.5mm) of silicon steel to reduce

eddy current loss. The armature is slotted and the armature winding is

housed in the slots.

(7). Armature Winding: It consists of several coils of insulated copper wire. Each coil may

have several turns. The coils are connected in series and parallel so

as to form either a lap winding or wave winding. The ends of the

winding are also connected to the commutator risers.

(8). Commutator: It is a cylindrical structure built up of copper segments. The copper

segments are insulated from each other by 0.8mm thick mica. The

commutator is useful to convert the AC induced in the armature

conductors and supply as DC to the external circuit.

(9). Shaft: The shaft carries the armature, commutator and bearings. The end covers house

the bearings and carry the weight of the armature.

(10). Eye Bolt: It is provided to lift the machine when required.

MEASUREMENT OF ARMATURE AND SHUNT FIELD RESISTANCE

Name Plate Details:

HP : RPM :

Voltage : Excitation Voltage :

Current : Excitation Current :

Apparatus Required:

Circuit Diagram:

S.No Apparatus Range Type Qnty

1 Ammeter 0-10A MC 1 NO

2 Ammeter 0-2A MC 1 NO

3 Voltmeter 0-30V MC ! NO

4 Voltmeter 0-300V MC 1 NO

5 Rheostat 270Ω, 1.5A Wire Wound 1 NO

6 Load 2.2KW, 230V Lamp 1 NO

220V

DC SUPPLY

+

-

A - +

V

-

+

D - Double

P - Pole

S - Single

T - Throw

S - Switch

Fuse

A

AA

220V

DC SUPPLY

+

-

A - +

V -

+

Measurement of Shunt Field Resistance

D - Double

P - Pole

S - Single

T - Throw

S - Switch

Fuse

Measurement of Armature Resistance

Precautions:

1. For measuring armature resistance, initially all the load must be in OFF position.

2. For measuring shunt field resistance, initially potential divider should be in minimum

position.

Procedure:

1. Connect the circuit as per the circuit diagram

2. Switch ON the supply to the circuit

3. For measuring armature resistance, vary the resistance in steps and note down the

readings of ammeter and voltmeter.

4. For measuring shunt field resistance, vary the potential divider in steps and note down

the readings of ammeter and voltmeter.

5. Tabulate the readings

6. From the readings, resistance is calculated by using the formula. R=V\I

Observations:

For Armature Resistance:

S.No

Armature

Current

(Amps)

Voltage Across Armature

(Volts)

Resistance,

R = V/ I

For Shunt Field Resistance:

Result:

S.No

Shunt Filed

Current

(Amps)

Voltage Across Shunt

Field (Volts)

Resistance,

R = V/ I

1

MAGNETIZATION CHARACTERISTICS OF DC SHUNT GENERATOR.

DETERMINATION OF CRITICAL FIELD RESISTANCE AND CRITICAL

SPEED

Exp.No:1 Date:


Aim : A) To obtain experimentally the magnetization characteristic of separately and

self excited DC shunt generator & Determine critical resistance and critical

speed.

Name Plate Details :

DC Motor DC Generator

Horse Power : KW Rating :

Voltage : Voltage :

Current : Current :

Speed : Speed :

Excitation Voltage : Excitation Voltage :

Excitation Current : Excitation Current :

Apparatus :

S.No Apparatus Range Type Quantity

1 Ammeter M.C 1 NO

2 Voltmeter M.C 1 NO

3 Rheostat Wire Wound 1 NO


5 Tachometer Digital 1 NO

To understand the significance of residual magnetism

To understand voltage build-up process

To determine Critical field resistance & Critical Speed

To understand the saturation of field poles

To understand different excitation methods

2

Circuit Diagram:

L F A

+

220V

DC SUPPLY

-

Fuse

D P S T

Switch

A

Z

ZZ AA

A

+ V

Z -

AA ZZ +

A

-

Potential

Divider

Open Circuit Characteristic of Separately Excited DC Shunt Generator

3

Procedure:

For Separately Excited :

1. Connect the circuit as per the circuit diagram.

2. Switch ON the DC supply on motor side.

3. Adjust the speed of the DC motor to rated value by varying the field rheostat

of motor.

4. Switch ON the DC supply across the field circuit of the generator.

5. Vary the field current of generator in steps and record the meter

readings until generated voltage is 125% of the rated value.

6. Switch OFF the supply after bringing rheostats to initial position.

Model Calculations:

From Graph:

Critical Resistance = RC =

Critical Speed = NC = N x

y in Volts

x in Amps

yz

xz

Where, N - Rated speed in RPM

Precautions :

1. Initially field rheostat of motor and generator are in minimum

and maximum position respectively.

4

Y

Observations :

For Separately Excited

Model Graph: Rc Rf

OCC

Induced

EMF y

Field Current

Result:

S.No

Field

Current (If)

Induced

EMF

(Eg)

Amps Volts

1

2

3

4

5

6

7

8

S.No

Field

Current (If)

Induced

EMF

(Eg)

Amps Volts

9

10

11

12

13

14

15

16

Z

x X

5

Learning objectives:

1. If the excitation is below its rated value the maximum part curve is linear and above the

rated value of excitation the curve is non-linear i.e the further increase of field current

will

not have any effect on terminal voltage of the generator.

2. The total magnetization characteristics are non-linear in nature.

3. The point of intersection of field winding resistance line with magnetization

characteristics

gives the rated no-load terminal voltage of the given generator.

4. As the steepness of the curve will increases with increase in field resistance and the

maximum value of generated emf at its terminals decreases.

Review Questions:

1. On what principle DC generator works?

2. Classify DC generators on the basis of excitation?

3. What is the standard direction of rotation of the DC generator?

4. What is meant by build – up of a generator?

5. What are the causes for failure of build-up voltage in shunt generator?

6. What are the parameters determined from the OCC curve?

7. What is critical resistance of a shunt generator? How it is determined?

8. What do you mean by critical speed of a shunt generator?

9. Why does saturation curve starts from some value higher than zero?

6

BRAKE TEST ON DC SHUNT MOTOR. DETERMINATION OF

PERFORMANCE CURVES

Exp.No:2 Date:


Aim : To determine the performance curves of DC shunt motor by conducting brake test.


DC Motor

Horse Power :

Voltage :

Current :

Speed :

Excitation Voltage :

Excitation Current :

Apparatus :


1 Ammeter MC 1 NO

2 Voltmeter MC 1 NO



To calculate efficiency by direct loading

To obtain Speed-Torque, Load-Torque characteristics

7

Circuit Diagram:

+

220 V

DC SUPPLY

-

Fuse

D - Double

P - Pole

S - Single

T - Throw

S - Switch

+ A

- -

+

V--

3 – POINT STARTER

L F A

A

Z

ZZ AA

Brake Drum

Brake Test on DC Shunt Motor

s1 s2

r

8

Procedure :


2. Switch ON the supply and start the motor on no-load and note down the

voltage and current at rated speed.

3. Step by step increase the load on the motor, and note down the meter

readings, values of spring balance and speed.

4. Repeat this procedure up to its full load current.

5. Gradually remove the load, switch OFF the supply.

Precautions :

1. Initially field rheostat should be in minimum.

2. Apply load up to its rated load current is reached.

Formulae Used:

Shaft Torque = Tsh = 9.81 (S1~ S2) R N-m

Where

S1 & S2 - Readings of spring balances

R - Radius of pulley ;N - Speed in RPM

Output Power = Po = 2πNTsh/60 Watt

Input Power = PI = VI Watt

Output Power Percentage Efficiency, %η = x 100

Input Power

9

Observations :

S.No

Voltage

( V )

Current

( I )

Speed

( N )

Spring

Balance

Torque

( T )

Output

Power

( Po )

Input

Power

( PI )

Percentage

Efficiency

( %η ) S1 S2

Voltage

(V) Amp RPM Kg Kg N-m Watt Watt %

1

2

3

4

5

6

7

8

Model graph:

:

S

p

e

e

d

Output

L

o

a

d

C

u

r

r

e

n

t

T

o

r

q

u

e

%

E

f

f

i

c

i

e

n

c

y

%η

N TSh

IL

10

Result :

Learning outcomes:

1. The fall in speed from no load to full load is small; hence these motors can be used

where a substantially constant speed is required. (Blowers, drilling machines, lathe

machines, centrifugal pumps, machine tools, etc..,)

2. From the output (Vs) speed curve, the shunt motor has a definite speed at no-load.

Hence it does not ‘run away’ when the load is suddenly thrown off.

3. From the efficiency – output curve the efficiency increases rapidly, reaches its

maximum value and then falls because of further increase in losses. Therefore to get

best performance from the D.C Motor, apply a load slightly less than the full-load.

4. From the Torque-output curve the torque developed increases linearly with the

increase in the load.

5. As this method consumes more power to calculate the efficiency, this method is

applicable only for small rating machines.

Review Questions:

1. Why brake test is performed with small machines only?

2. What is the main draw back for determining efficiency in brake test?

3. What are the applications of dc shunt motor?

11

SWINBURNE’S TEST AND PREDETERMINATION OF EFFICIENCIES AS

GENERATOR AND MOTOR

Exp.No: 3 Date:


Aim : To determine the performance curves of DC shunt motor by conducting

Swinburne’test.


DC Motor

Horse Power :

Voltage :

Current :

Speed :



Apparatus :


1 Ammeter

MC 1 NO

2 Ammeter

MC 1 NO

3 Voltmeter

MC 1 NO

4 Voltmeter

MC 1 NO

5 Rheostat Wire

Wound 1 NO

6 Tachometer

Digital 1 NO

7 Load

Resistive 1 NO

8 SPST Switch Knife

Type 1 NO

To calculate the no-load losses

To measure armature resistance

To pre-determine the efficiency as generator & as a motor at different loads

12

Circuit Diagram:

3 – POINT STARTER

Fuse

+ + A

- A AA

220V

DC

SUPPLY

D - Double

P - Pole

S - Single

T - Throw

S - Switch

+ V -

-

Drop Test ( Armature Resistance )

Variable

Resistive Load

L F A

+ Fuse SPST Switch

D - Double

P - Pole

S - Single

T - Throw

S - Switch

+ A

-

A 220V

DC SUPPLY Z

+ V

-

- ZZ AA

A

Swinburne’s Test

+

-

13

For Swinburne’s Test:

Formulae Used

No load armature current = Iao = ILo - If

Constant losses, Wc= No load input - No load copper losses.

= VILO - Iao2Ra

For Generator :

Output VIL

Percentage Efficiency, %η = x 100 = Input VIL + Total Losses

VIL

=

VIL + (Constant Losses + Copper losses)

For Motor:

Output

Percentage Efficiency, %η = x 100

Input

Input - Total losses

= x 00

Input

Procedure :


2. Close the SPST switch and start the motor, adjust the speed to reach its rated

value using field rheostat.

3. Open the switch and note down the meter readings.

4. Switch OFF the supply after bringing the rheostat to initial position.

5. Calculate the armature resistance by conducting drop test.

Precautions :

1. Make sure that the field rheostat is in the minimum position initially.

14

Observations :

S.No

No Load Voltage

(V)

No Load Current

(ILO)

Field Current

(If)

Volt Amp Amp

1

Drop Test :

S.No

Armature Voltage

(V)

Armature Current

(Ia)

Armature Resistance

(Ra)

Volt Amp Ohm

1

2

3

4

5

As a Motor :

S.No

Load

Armature

Current ( Ia )

Input

Power

Total

Losses

Output

Power

Percentage

Efficiency

Amp Watt Watt Watt %

1

Full Load

2 ¾ th

Full Load

3 ½ th

Full Load

4 ¼ th

Full Load

15

As a Generator:

S.No

Load

Armature

Current

( Ia )

Input

Power

Total

Losses

Output

Power

Percentage

Efficiency


1 Full Load

2 ¾ th Full Load

3 ½ th

Full Load

4 ¼ th

Full Load

Model Graph :

Output

%

E

f

f

i

c

i

e

n

c

y

%ηG

%ηM

16

a a

a a

a a

a a

Model Calculations :

No load input = Po = VILO

No load armature current = Iao = ILO – If

No load armature copper loss = Iao2 Ra

Constant losses, Wc= No load input – No load armature copper loss

As a Motor :

For ¾ th

load :

Line current = IL = (3/4) x Rated value

Armature current = Ia= IL – If.

Armature copper loss = I 2 R

Total losses = I 2R + Constant losses

Input Power = VIL

Output Power = Input – Total losses

Output

Percentage Efficiency = %η = x 100

Input

As a Generator :

For ½ load :

Line current = IL = (1/2) x Rated value

Armature current = Ia = IL + If

Armature copper loss = I 2 R

Total losses = I 2R + Constant losses

Output Power = VIL

Input Power = Output + Total losses

Output

Percentage Efficiency = %η = x 100

Input

Efficiencies at different loads are calculated and graph is plotted.

17

Result:

Learning outcomes:

1. The efficiencies are determined without actually applying the load. Hence the power

consumed is very less compared with direct test. So this method is economical.

2. The efficiency of the dc machine is greater when it runs as generator than as a motor.

3. At any desired load we can able to pre-determine efficiency of a dc machine.

4. The time taken to calculate efficiency is less.

5. Since the temperature variations are not considered, this method is not an exact

method of determining the efficiency accurately.

Review Questions:

1. Why Swinburne’s test is considered convenient and economical method for

testing dc shunt machines?

2. Why Swinburne’s test can not perform on dc series machines?

3. Why constant losses can be considered equal to input to a machine at no-load?

18

HOPKINSON’S TEST ON DC SHUNT MACHINES

PREDETERMINATION OF EFFICIENCY

Exp.No: 4 Date:


Aim: To pre-determine the efficiency of a pair of DC shunt machines conducting

HOPKINSON’S test.


DC Motor DC Generator

Horse Power : KW Rating :

Voltage : Voltage :

Current : Current :

Speed : Speed :

Excitation Voltage : Excitation Voltage :

Excitation Current : Excitation Current :

Apparatus :


1 Ammeter

MC 2 NO

2 Ammeter

MC 3 NO

3 Voltmeter

MC 1 NO

4 Voltmeter

MC 1 NO

5 Voltmeter

MC 1 NO


7 Rheostat

Wire Wound 1 NO


9 Load

Resistive 1 NO

10 SPST Switch Knife Type 1 NO

To measure armature resistance, To calculate the losses

To pre determine the efficiency as generator & as a motor at different loads

19

SPST Switch

3 – POINT STARTER + V -

220V

Fuse +

D - Double

P - Pole

A - +

A

-

_

A

+ +

V

-

Z A A

Z SUPPLY

T - Throw S - Single

+

-

S - Switch

ZZ AA AA

ZZ +

A

-

A F L

Circuit Diagram:

DC

HOPKINSON’S TEST

Fuse

+ + A - A AA

220V

DC SUPPLY

-

D - Double

P - Pole

S - Single

T -Throw

S - Switch

+ V -

Variable

Resistive Load

Drop Test ( Armature Resistance )

20

Procedure :

1. Note down the name plate details of both machines.


3. Before starting the motor, SPST switch is kept open.

4. The motor is started using 3-point starter and the speed of the motor is

adjusted to its rated value by varying the field rheostat.

5. The generator field rheostat is adjusted so that the voltage of generator and

supply voltage are equal.

6. Now the voltage across the SPST switch is zero.i.e.the two machines can run

parallel, the SPST switch may be closed.

7. Adjust the field rheostat of the generator step by step by keeping speed

constant and the readings of all the meters to note down.

8. Bring the generator field rheostat to read generator armature current to zero,

then open SPST switch and switch OFF the supply.

Precautions :

1. Initially the parallel switch is in open position.

2. Initially field rheostat of motor and generator must be at minimum and

maximum positions respectively.

Formulae Used:

Input Power to the set = Total losses in both the machines

Input power to the set – Copper losses of motor and generator

Stray losses = 2

For Motor :

Percentage Efficiency, %η =

For Generator :


Input Power - Losses

Input Power

Output Power

Output Power + Losses

21

Observations :

S.No

Line

Voltage

(VL)

Line

Current

(IL)

Motor Current Readings

Generator Current Readings

Armature

Current

(IAM)

Field

Current

(IFM)

Input

Current

(ILM)

Armature

Current

(IAG)

Field

Current

(IFG)

Output

Current

(ILG)

Volt Amp Amp Amp Amp Amp Amp Amp

1

Drop Test :

S.No

Armature Voltage

(V)

Armature Current

(Ia)

Armature Resistance

(Ra)

Volt Amp Ohm

1

2

3

4

5

As a Motor :

S.No

Load

Armature

Current

( Ia )

Input

Power

Total

Losses

Output

Power

Percentage

Efficiency


1 Full

Load

2 ¾ th Full

Load

3 ½ th Full

Load

4 ¼ th Full

Load

22

As a Generator :

S.No

Load

Armature

Current

( Ia )

Input

Power

Total

Losses

Output

Power

Percentage

Efficiency


1 Full

Load

2 ¾ th Full

Load

3 ½ th Full

Load

4 ¼ th Full

Load

Model Graph :

Load Current

%

E

f

f

i

c

i

e

n

c

y

%ηG

%ηM

23

AG AG FG AM AM FM S

AG AG

Model Calculations :

Input Power to the set = VIL

Input Power to the set = Total Losses in both the machines

VIL = I 2R + VI + I

2R + VI + 2W

VIL -[ I 2R + VI + I

2R + VI ]

Stray Losses, Ws = AG AG FG AM AM FM

2

Load Current of generator, ILG = IAG – IFG

Input Power to the Motor = VILM (Where, ILM = IAM + IFM)

Output Power of the Generator = VILG

Armature Copper Loss of Generator = I 2R

Field Copper Loss of Generator = IFG2RFG (or) VIFG

Armature Copper Loss of Motor = IAM2RAM

Field Copper Loss of Motor = VIFM

For Motor :

Motor Input Power = VILM

Losses = Armature Copper Loss + Field Copper loss + Ws

Motor Input Power - Losses


For Generator :

Generator Output Power = VILG

Motor Input Power

Losses = Armature Copper Loss + Field Copper loss + Ws

Generator Output Power


Generator Output Power + Losses

Result :

24

Learning outcomes:

1. From the experiment, observed that the power drawn from the supply mains is less.

2. This method is more accurate in determining the efficiency than Swinburne’s test since

the temperature effect is included in the copper losses.

3. From the characteristics it has been observed that the efficiencies of motor and

generator are almost equal for s because of the stray losses are assumed to be same for

both the machines.

Review Questions:

1. What condition must be fulfilled before connecting two shunt machines back-

to-back?

2. What are the merits of Hopkinson’s test?

3. What happens if SPST switch is closed before connecting the machines in

parallel?

4. Usually at how much percentage of load maximum efficiency of machine

occurs?

5. What is the draw back of Hopkinson’s test?

25

SPEED CONTROL OF DC SHUNT MOTOR BY FIELD AND ARMATURE

CONTROL

Exp.No: 5 Date:


Aim : To control the speed of DC shunt motor by

1) Field Control method 2) Armature Control method


DC Motor

Horse Power :

Voltage :

Current :

Speed :



Apparatus :


1 Ammeter MC 1 NO

2 Voltmeter MC 1 NO




To understand the speed control by flux control method

To understand the speed control by armature control method

To understand the significance of Starter of dc motor

26

Circuit Diagram:

3 – POINT STARTER

L F A

+

220V

DC SUPPLY

Fuse

D - Double

P - Pole Z A

S - Single

T - Throw +

S - Switch V

- ZZ AA

+ A

-

Speed Control of DC Shunt Motor

-

27

Procedure :


2. Switch On the supply and start the motor using starter.

3. To increase the speed we use field control method.

In this, keep the voltage across armature terminals constant and vary the field

current up to rated value using field rheostat and note down the speed for

various values of field current

4. To decrease the speed we use armature control method.

In this, keep the field current constant and vary the voltage across the

armature terminals by using armature rheostat and note down the speed for various

values of armature voltages.

5. Switch OFF the supply after the motor is brought to the initial state.

Precautions :

1. Initially the rheostats should be at minimum positions.

2. Vary the rheostats up to the rated field current and armature voltage.

Observations :

Field Control Method

Va = (Constant)

Armature Control Method

If = (Constant)

S.No

Armature

Voltage

Speed

(N)

Volt RPM

S.No

Field

Current (If)

Speed

(N)

Amp RPM

1

2

3

4

5

6

7

8

28

Model Graph :

S

p

e

e

d

Result:

Learning objectives:

1. The addition of resistance in the armature path causes to decrease the voltage across the

armature hence decrease in speed of the motor.

2. The addition resistance in the field path causes to decrease the field current hence increase

in speed of the motor.

Review Questions:

1. What are the speed controlling methods of dc shunt motor?

2. Is there any change in armature current in armature control method?

3. Is there any change in armature current in flux control method?

4. Why is field control considered superior to armature resistance control

for dc shunt motor?

5. What will effect the change in supply voltage on the speed of dc shunt

motor?

6. Why starters are used for dc motors?

7. Why NVC is provided in dc motor starter?

If = (Constant)

V = (Constant)

Armature

Voltage

29

O.C. & S.C. TESTS ON SINGLE PHASE TRANSFORMER

Exp.No: 6 Date:

AIM:- To find equivalent circuit parameters, regulation and efficiency of a Single

Phase Transformer by conducting OC & SC tests.

NAME PLATE DETAILS:

Transformer Autotransformer

APPARATUS:-

S.No. APPARATUS TYPE RANGE/RATING QUANTITY

30

CIRCUIT DIAGRAM :

31

PROCEDURE:-

Open Circuit Test:

1. Connect the circuit as per the circuit diagram. 2. Autotransformer is set to zero Output voltage position and switch on the

supply.

3. Adjust the autotransformer till the voltmeter reads rated voltage of

Transformer Primary.

4. Note down the readings of wattmeter, voltmeter and ammeter in table1 5. Calculate Zo and Ro from the readings.

Short Circuit Test:


2. Autotransformer is set to zero output voltage position and switch on the

supply

3. Adjust the autotransformer till the ammeter reads rated current of

Transformer primary

4. Note down the reading of wattmeter, ammeter & voltmeter in table 2

5. Calculate the total resistance & Leakage reactance from the SC Test

results.

6. Calculate voltage regulation & efficiency from the test results.

PRECAUTIONS:

1. Connections should be tight, avoid loose connections. 2. Correct meters should be selected from name plate details.

3. While doing the experiment that the readings for meter should not exceed

rated value

4. Note down readings without parallax error.

32

OBSERVATIONS :

OC Test :

S.No No-Load Voltage

Vo in volts

No-Load current

Io in amps

Wattmeter

reading Wo in watts (Wi)

SC Test:

S.No. Short-circuit

voltage Vsc in

Volts

Short-Circuit current

Isc in amps

Wattmeter

reading

Wsc in watts

(Wc)

CALCULATIONS :

OC Test:

No-Load Power Factor (Cos Ø) =

Wo

VoIo

No- Load Power Factor Angle (Øo) = Cos-1(

Wo )

VoIo

Working component of No-Load current (Iw) = Io Cos Øo Magnetizing Component of No-load current (Iµ) = Io Sin Øo

Shunt branch resistance (Ro) = Vo

Iw

Shunt Branch Reactance (Xo) = Vo

Iµ

33

2 2

SC Test:

Equivalent impedance referred to secondary is (Zo2 )=

Equivalent Reactance referred to secondary is (Xo2) =

Vsc

Isc

(Zo )2

(Ro )

2

Where Ro2 = Wsc

(Isc)2

Equivalent resistance referred Primary is (Ro1) = Ro2

K 2

Equivalent reactance referred to primary is (Xo1) = Xo2

K 2

To find % Voltage regulation :

At 0.8 PF lagging %VR =

At 0.8 PF Leading %VR =

At Unity Power factor: %VR =

V2

V2

I 2 (Ro2 CosØ2 ) X 100

V2

X100

X100

To Find efficiency :

At x load: η =

xV2 I2CosØ2

X100 xV I CosØ x2Wcu Wi

2 2 2

I 2 (Ro2 CosØ2 Xo2 SinØ2 )


34

Io

Iµ Iw

Xo

Ro

1.0pf

0.8pf

0.6pf

0.4pf

0.2pf

EQUIVALENT CIRCUIT : R1 X1

115V 230V

MODEL GRAPHS :

Efficiency in %η

Short Circuit current in amps

RESULTS

+ Regulation X=1

X=3/4

X=1/2

X=1/4

Leading pf Unity Lagging pf

-ve Regulation

35

SUMPNER’S TEST ON A PAIR OF SINGLE PHASE TRANSFORMERS

Exp.No: 7 Date:

AIM :

To find equivalent circuit parameters, regulation & efficiency of two identical

Transformers by conducting sumpner’s test.

NAME PLATE DETAILS:

Transformer -1 Transformer -2 Autotransformer

APPARATUS REQUIRED:-

S.No. APPARATUS TYPE RANGE QTY

1. Voltmeter 1

2. Voltmeter 1

3. Ammeter 1

4. Ammeter 1

5. Wattmeter 1

6. Wattmeter 1

36

CIRCUIT DIAGRAM :

PROCEDURE:


2. Keep the switch ‘s’ Open and autotransformer 2 at zero position 3. switch on the supply and vary the autotransformer-1, such that voltmeter indicates

rated voltage.

4. At this position note down V1, A1,W1 readings in table-1

5. Now close switch ‘S’ and adjust autotransformer-2, such that ammeter A2 reads

rated current at this position note down V2, A2, W2 readings in table-2

6. Calculate these equivalent circuit parameters regulation and efficiency from the

readings.

PRECAUTIONS:

1. Connections should be tight, avoid loose connections.

2. Correct rated meter should be selected from the name plate details.

3. While doing the experiment, See meter reading should not exceed rated

values.

4. Note down the readings without parallax error.

37

(

2

Observations:

S.No. Vo in Volts Io in Amps Wo in Watts

S.No. Vsc in Volts Isc in Amps Wsc in Watts

CALCULATIONS: Io

2

Wo

=

2

No-Load Power Factor (Cos Ø) = Wo

VoIo

No- Load Power Factor Angle (Øo) = Cos-1 Wo ) VoIo

Iron loss or Working component of No-Load current (Iw) = Io Cos Øo

Magnetizing Component of No-load current (Iµ) = Io Sin Øo Vo

Shunt branch resistance (Ro) = Iw

Shunt Branch Reactance (Xo) = Vo

Iµ

SC Test:

Vsc

2

Wsc

2

Equivalent impedance referred to secondary is (Zo2 )=

Equivalent resistance referred to secondary is (Ro2) =

Equivalent Reactance referred to secondary is (Xo2) =

Vsc

Isc

Wsc

Isc2

(Zo2 )

(Ro )2

Equivalent resistance referred Primary is (Ro1) = Ro2

K 2

Equivalent reactance referred to primary is (Xo1) =

Where K = V2

V1

Xo2

K 2

2

38

Io

Iµ Iw

Xo

Ro

To find % of Voltage regulation :

At 0.8 PF lagging;

%VR = 2

At 0.8 PF Leading

%VR = 2

X100

X100

At Unity Power factor:

%VR = I 2 (Ro2 CosØ2 ) X 100

V2

To Find efficiency :

At x load:

Efficiency η =

xV2 I 2 CosØ2

X100

Equivalent Circuit:

R1 X1

115V 230V

Table

S.No Efficiency η Out put

Lagging Leading Power factor Cos ᴓ



xV I CosØ x 2Wcu Wi 2 2 2

V

V

39

1.0pf

0.8pf

0.6pf

0.4pf

0.2pf

MODEL GRAPHS

Efficiency in %η

Short Circuit current in amps

RESULT:

Viva voice :

1. How can you determine the efficiency of a transformer ?

2. What are the difference in sumpener’s test and open circuit and short circuit tests

?.

3. which windings of the transformers are connected in parallel in this test ? 4. How the secondary windings of the transformers are connected for conducting the

sumpner’s test?

5. What do you mean by phase opposition in reference to sumpner’s test on

transformers?

6. How much voltage is applied on the primary side while conducting the sumpner’s

test?

7. How much voltage is applied on the secondary side while performing the

sumpner’s test on transformers?

+ Regulation X=1

X=3/4

X=1/2

X=1/4

Leading pf Unity Lagging pf

-ve Regulation

40

3

2

SCOTT CONNECTION OF TRANSFORMERS

Exp.No: 8 Date:

AIM : To Convert 3-Phase supply into single phase supplies by the method of scott

connection and to verify the following criteria.

1. Teaser transformer primary has Times the turns of main primary. But

volt/turn is the same. Their secondaries have the same turns, which results in

equal secondary terminal voltages.

2. If main primary has N1 turns and main secondary has N2 turns, then main

transformer ratio is N2/N1. However, the transformation ratio of teaser will be

equal to 1.15 times of transformation ratio of main.

3. if the load is balanced on one side, it is balanced on the other side as well

4. Under ;balanced load condition, main transformer rating is 15% greater than that

of the teaser.

5. The currents in either of the two halves of the main primary are the vector sum of

KI2M and 0.58KI2T(or 0.5IIT)

Main Transformer Teaser Transformer Autotransformer

APPARATUS REQUIRED:-


1. Voltmeter

2. Ammeter

3. Ammeter

4. Multi meter

41

CIRCUIT DIAGRAM :

42

PROCEDURE:

1. Connect the Circuit as per the circuit diagram 2. Keep the secondary of both teaser and main Transformers open and voltage is

applied with 3-Phase autotransformer until rated voltage is appeared across the

secondary.

3. Note down the input and output voltages of teaser and main transformers and

also combined voltage in table-1 with multi meter.

4. Load the secondary of main Transformer and teaser Transformer equally then

note down voltages in table-1 and ammeter readings in table-2.

5. Calculate the Transformation ratios of teaser and main Transformer.

PRECAUTIONS:

1. Connections should be tight, avoid loose connections.

2. Correct rated meters should be selected from the name plated details. 3. while doing the Transformer experiment see that the meter readings should not

exceed its rated value.


5. While giving the connections identify the tapping on the Transformer.

6. The Load on the both the Transformers should not exceed the rated value.

Observations:

Table -1

S.No Primary voltage Secondary voltage Veification

Teaser

T/F VPT

in Volts

Main

T/F VPM

in Volts

Teaser

T/F TST

in Volts

Main

T/F TSM

in Volts

Combined

VSC in

Volts

VSC =

V 2

ST

Volts

V

SM

2 in

Table -2 S.No Primary current Secondary current Verification

I1 in

Amps

I2 in

Amps

I3 in

Amps

Teaser

T/F

IT = I4

Main T/F

IM = I5(A)

Combined

IC = IO

IC =

I 2

M

amps

I

T

2 in

43

Calculations:

Main Transformer turns ratio (K

M) =

VSM

V

Teaser Transformer turns ratio (K

T) =

PM

VST K M

VPT KT

Result:

Viva voce: 1. What is the aim of scott connections of Transformers? 2. How many transformers are needed for scott connection?

3. What are the special conditions to be satisfied by the transformer to be used for scott

connection.?

4. Where does the scott connections find it use?

5. If the two transformers are used in scott connections are identical, then how many primary

turns of the teaser transformer are actually used?

6. What phase difference should exist in the two secondary voltages if two identical

transformers connected in scott connection?

44

PARALLEL OPERATION OF SINGLE PHASE TRANSFORMERS

Exp.No: 9 Date:

AIM:-

To operate the single phase Transformers in parallel and to supply load sharing of

each Transformer.

NAME PLATE DETAILS:

Transformer Autotransformer

APPARATUS:-


1. Transformer core 115/230V, 1-Ø,2KVA 2

2. Voltmeter MI (0-150)V 1

3. Voltmeter MI (0-500)V 1

4. Ammeter MI (0-5)A 1

5. Ammeter MI (0-10)A 1

6. Resistive load 220V, 10A 1

7. Autotransformer 1-Ø (0-230)/270V, 15A 1

45

CIRCUIT DIAGRAM :

46

PROCEDURE:-

POLARITY TEST:

1. The circuit ;is connected as per the circuit diagram.

2. Rated voltage is to be applied to the windings of the Transformer with the help

of autotransformer.

3. If the voltmeter connected across secondary side reads zero the polarity of the

Transformers connected in subtractive.

4. if the voltmeter reading is twice the rated value then two Transformers are sid

to be in additive polarity.

LOAD TEST:

1. Connect the circuit as per the circuit diagram

2. Rated voltage is applied to Transformer with the help of Autotransformer.

3. The load on the secondaries of the two Transformers is varied in steps and ammeters

readings are noted.

4. Repeat the steps upto 4 to 5 readings.

PRECAUTIONS:

1. Before starting are after Completion of the experiment autotransformer should be kept

in zero position.

2. The polarity should be checked carefully before paralleling the Transformers

3.While loading, the Transformers should be taken so that, the load curret does not

exceed rated value.

OBSERVATIONS:

S.No Current supplied by Transformer I1 in

Amps

Current Supplied by

Transformer I2 in amps

Total Current I3

in Amps

Verification

I I 2

I 2

3 1 2

RESULTS:

QUESTIONS : -

1. When is the parallel operation of transformer is required.

2. What is the condition to be satisfied before paralleling two transformers.

3. How much circulating current can be tolerated for parallel operation of transformers?

4. What will happen if two transformers are connected in parallel with wrong polarity?

47

SEPARATION OF LOSSES IN A DC SHUNT MOTOR

Exp.No: 10 Date:

Aim: To separate the hysteresis & eddy current losses from stray losses of a DC shunt Motor.

Apparatus:

Ammeter-(0-2)A, MC – 1 no.

Voltmeter – (0-300)V, MC– 1 no.

Rheostat- 350Ω/ 1.2A–1 no., 50Ω/ 5A–1no

3-PointStarter - 5 HP – 1 no.

Tachometer.

Connectingwires

NamePlateDetails:

DC Motor

KW-

Voltage-

Current– RPM –

WDG – Exc. –

Circuit Diagram:

Procedure:


2. Keep both field and armature rheostats at minimum position Maximum position

respectively and start the motor by using starter and bring to rated speed by adjusting field

rheostat.

3. Note down all the meter readings, repeat this by varying armature rheostat. The field

current to be kept constant.

4. Adjust the field to another suitable value and repeatstep-3

5. Find the armature resistance by conducting the experiment.

Precautions:

1. Check all the apparatus before making connections.

2. Field rheostat should be in minimum position.


4. Don’t touch any wire, terminals or apparatus when the supply is ON.

5. Start the machine without any load (mechanical or electrical).

N

N +

Tabular column:

Underfullexcitation:

Under half excitation:

S.No

Va

Ia

Speed (N) I 2R

a a

Tota

lLoss

W(stra

ylosse

W/N

Theoretical Calculations:

Total Losses = VaIa(under no loadcondition)Armature

resistanceRa= 2

IaRa= Copper Losses 2

Total Losses =Ia Ra+IronLosses +FrictionLosses

IronLosses (20 to 30%) =HysteresisLosses + EddyCurrent Losses

FrictionLosses(10to 20%) = MechanicalLosses +WindageLosses

(WindageLossesarenegligible)

Copper Losses (30 to 40%)

StrayLosses=IronLosses +FrictionLossesW(StrayLosses) = AN +B 2

CN+ D 2

Where AN + 2 BN =FrictionLosses

CN+ D 2

= IronLosses

S.No

Va

Ia

Speed (N) I 2Ra

a

Tota

lLoss

W(stra

ylosse

W/N

CN=HysteresisLosses

2 DN =Eddy current losses

Graphs:(Speed(N) vsW/Nratio).

Result:

electrical machines- i laboratory manual...the electrical machines-i lab evaluation can be broadly...

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