ME 39-Electrical Engineering Lab Manual

EINSTEIN COLLEGE OF ENGINEERING Sir.C.V.Raman Nagar, Tirunelveli-12

Department of Electrical & Electronics Engineering

Subject Code: ME 39

“Electrical Engineering Lab”

Name : ……………………………………

Reg No : ……………………………………

Branch : ……………………………………

Year & Semester : ……………………………………

ME 39 Electrical Engineering Lab

©Einstein College of Engineering

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TABLE OF CONTENTS

S.No Date Name of the Experiment Page No.

Marks Staff Initial

Remarks

1 Open Circuit Test and Load Test on Separately

Excited Dc Generator

2 Load Test on Dc Shunt Motor

3 Load Test on Dc Series Motor

4 Speed Control of Dc Shunt Motor

5 Load Test on 3φ Squirrel Cage Induction Motor

6 Load Test on Single Phase Induction Motor

7 Regulation of Three Phase Alternator By EMF

And MMF Methods

8 V Curves and Inverted V Curves of Three Phase

Synchronous Motor

9 Load Test on Single Phase Transformer

10 Open Circuit and Short Circuit Test on Single

Phase Transformer

11 Speed Control of Three Phase Slip Ring Induction

Motor

12 Study of DC and AC Starters



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OC & LOAD TEST ON SEPERATELY EXCITED GENERATOR

NAME PLATE DETAILS:



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AIM:

To conduct the open circuit test on a given separately excited DC generator

and to draw the characteristics curves

APPARATUS REQURED:

S.No Apparatus Range Quantity

1 Ammeter (0-2A)MC

(0-20A)MC

1

2

2 Voltmeter (0-300V)MC 1

3 Rheostat 300/1.1A

210/2A

1

1

4 Tachometer - 1

5 Resistive load 5Kw 1

FORMULAE USED:

Ia= IL

Eg = VT+IaRa

Where,

VT is the terminal voltage

Ra is the armature resistance

Ex.No. OPEN CIRCUIT TEST AND LOAD TEST ON SEPARATELY EXCITED DC

GENERATOR Date:



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TABULATION:

OPEN CIRCUIT TEST

Field current If(A) Open circuit voltage

Eg(V)

To find Ra

S.No Armature current

Ia(A)

Armature voltage

Va (V)

Ra=Va/Ia(Ohms)



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Ia is the armature current

IL is the line current

Eg is the generated emf

THEORY:

In separately excited DC generator the exciting field current is supplied by a

separate source. The terminal voltage applied across the armature can be taken as

the induced voltage. Thus it is possible to obtain the open circuit voltage as a

shunt of field current. By field rheostat variation we can vary the field current.

Hence we can obtain the variations in the no load voltage. Because of the residual

flux in the magnetic poles so far, there is a small amount of emf is induced, even

when the field current is zero. Since the generated emf is directly proportional to

the flux, the open circuit characteristic is a straight line at initial position.

PROCEDURE:

NO LOAD TEST

1. Connections are made as per the circuit diagram

2. The motor is started with the help of the three-point starter and it is made to run it

rated speed when the generator is disconnected from the load by DPST switch.

3. By varying the generator field rheostat gradually, the open circuit voltage (E0) and

corresponding field current (If) readings are observed at no load condition

4. The motor is switched off by using the DPST switch after bringing all the rheostats

to initial position

LOAD TEST

1. Connections are made as per the circuit diagram



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LOAD TEST

Line

Voltage

VL (V)

Field current

If (A)

Load current

IL(A)

Armature

current Ia(A)

Armature drop

IaRa(V)

Eg= VL+IaRa



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2. The motor is started with the help of the three-point starter and it is made to run it

rated speed when the generator is disconnected from the load by DPST switch.

3. By varying the generator field rheostat gradually the rated voltage is obtained

4. The ammeter and voltmeter readings are observed at no load condition

5. The ammeter and voltmeter readings are observed for different load up to rated

current by closing the DPST switch.

6. After tabulating all the readings the load is brought to initial positions.

7. The motor is switched off using the DPST switch after bringing all the rheostat to

initial position.



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MODEL GRAPH



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MODEL CALCULATION:

RESULT:



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DISCUSSION QUESTIONS

1. Purpose of this experiment?

2. How will you bring the Dc generator to its rated speed?

3. What is mean by external resistance?

4. How will you find the armature resistance?

5. Condition of excited on open circuit?

6. What will happen it you interchange the shunt field connection?

7. What will happen in shunt generator if load is applied?

8. What is the maximum voltage in shunt generator?

9. What is commutator?

10. Write the relation between load and terminal voltage or generator voltage



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LOAD TEST ON DC SHUNT MOTOR

NAME PLATE DETAILS:



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AIM:

To conduct the load test on DC shunt motor and draw its performance

characteristic.

APPARATUS REQUIRED:

S. No Apparatus Range Quantity

1. Voltmeter (0-300)V mc 1

2. Ammeter (0-20A)mc 1

3. Rheostat 500Ω,0.8A 1set

4. Connecting wire As required

5. Tacho meter 1

FORMULAE USED:

1. Torque T=T1~T2*9.81*r*Nm

Where, (T1~T2) - Difference in the load

r – Radius of brake drum.

2. Power P= VLIL watts

VL – Line Voltage

IL – Line current

3. Output power = 2πNT/60 watts

Where, N – Speed in rpm

T – Torque in Nm

4. Efficiency (η) = O/p/I/p *100%

Ex.No. LOAD TEST ON DC SHUNT MOTOR Date:



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TABULATION: S.No VL (v) IL (A) T1 (kg) T2 (kg) T1~T2 N (rpm) Torque

(NM) I/P (w)

O/P (w)

% η



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THEORY:

The shunt motor has a definite no load speed the drop in speed from no

load to full load is small is 5 to 10% of no load speed. So the motor is usually

referred to as constant speed motor. The speed for any load within the

operating range of the motor can be readily obtained by varying the field

current by means of field rheostat. The shunt motor has a lower starting

torque. If twice full load torque is required at starting then the shunt motor

draws the full load current. To start a shunt motor it should have enough

starting torque and the armature current should be within its safe limit. A there

point starter is used for the shunt motor. The efficiency curve usually of the

same shape for all motors or generator.

PROCEDURE:

i) Connections are made as per the circuit diagram.

ii) Set the rheostat at minimum position and start the motor using

starter. By varying the rheostat set the rated speed of the motor.

iii) Note down the speed, ammeter and voltmeter readings for

various load.

iv) The graph is plotted between output and various efficiency, line

current, torque and speed.



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MODEL GRAPH

PERFORMANCE CHARACTERISTICS

ELECTRICAL CHARACTERISTICS

MECHANICAL CHARACTERISTICS



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MODEL CALCULATION:

RESULT:



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DISCUSSION QUESTIONS:

1. What is the other name for DC shunt motor?

2. What is the field winding nature in DC shunt motor?

3. How will you connect the field winding in DC shunt motor?

4. What is the purpose of this experiment?

5. Relation between load & speed?

6. Relation between efficiency & load?

7. What is speed nature of shunt motor?

8. What is the starting torque nature of DC shunt motor?

9. What is the application of D shunt motor?

10. Whether we can run the DC shunt motor initially with load or without load?

11. Whether the field rheostat is kept in maximum or minimum position during initial

Condition?



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LOAD TEST ON DC SERIES MOTOR 3 point starter

NAME PLATE DETAILS:



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AIM:

To conduct the load test on DC Series motor and draw its characteristic.

APPARATUS REQUIRED:

FORMULAE USED:


T1~T2 - Difference in load

r – Radius of the break drum.

2. Input power = VLIL watts

VL – Line Voltage

IL – Line current

3. Output power = 2πNT/60 watts

N – Speed in rpm

T – Torque in Nm

4. Efficiency (η) = Output/Input *100

Ex.No. LOAD TEST ON DC SERIES MOTOR Date:


1 Voltmeter (0-300)V mc 1

2 Ammeter (0-15)A 1

3 3Point starter 1

4 Tachometer 1

5 Connecting wire 1



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TABULATION: S.No VL

(v) IL (A)

TL (kg)

T2 (kg)

T1~T2 N(rpm) Torque (nm)

I/P (w) O/P (w)

% η



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THEORY: It is early observed that at no load the motor current and hence the flux per

pole tends to zero and as a consequence the motor speed tends to increase to infinite.

This is a dangerous situation and the centrifugal force will destroy the armature flux a

series motor must never to allowed to run at no load torque increases the motor speed

drops heavily there by the KW load on the motor of this type of speed torque

characteristics and is ideally switched for function, cranes, etc., Application were as

during starting a large accelerating torque is demanded by the load is at ways on the

motor to there is no danger of under loading or no-loading.

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. Apply some load to the break drum and then start the motor.

3. Note down the speed and load current.

4. Just by increasing the load note down the voltmeter, Ammeter readings.

5. Note down the speed torque and load current various load up to the rated

current.



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MODEL GRAPH PERFORMANCE CHARACTERISTICS

ELECTRICAL CHARACTERISTICS MECHANICAL CHARACTERISTICS



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MODEL CALCULATION: RESULT:



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1. What is the starting torque nature in DC series motor?

2. What is the other name for DC series motor?

3. What is the field winding nature for DC series motor?

4. How will you connect field winding in series motor?


6. Application of DC series motor?

7. How will you differentiate torque curve between DC series, DC shunt and DC

Compound motor?

8. Whether we can run the DC series motor initially with load or without load?

9. Which starter is used for DC series motor?

10. What is the speed nature of DC series motor?



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SPEED CONTROL OF DC SHUNT MOTOR

NAME PLATE DETAILS:



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AIM:

To control the speed of the dc shunt motor by using armature control and field

control method.

APPARATUS REQUIRED:


1 Voltmeter (0-300v)mc

2 Ammeter (0-10A)mc

3 Rheostat (50Ω,5A),(500Ω,8A)

4 Connecting wire 1 set

THEORY

Field control Method:

We know that N1/Φ by decreasing the flux the speed can be

increased vice versa the flux could be changed by changing Ish with the help of a field

rheostat has to carry only a small current which means I2R losses is small so that

rheostat is small in size. This method is therefore efficient in non Interpol or machine

the speed could increase in the ratio 2:1. Any further weakening of flux effect the

commutation and hence put a limit to the maximum speed obtained with this method.

ARMATURE CONTROL METHOD:

This method is used when the speed below the no load speed are required. As

the supply voltage is normally a constant the voltage across armature is varied by a

variable resistance is series with the armature circuit. As this resistance increase a

potential difference across the armature decreased by decreasing the armature speed.

Ex.No. SPEED CONTROL OF DC SHUNT MOTOR Date:



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TABULATION: S.No Armature control method

If= A If= A If= A Var Nrpm Var Nrpm Var Nrpm

S.No Field control method

Va= v Va= v Va= v If(A) Nrpm If(A) Nrpm If(A) Nrpm



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PROCEDURE:

The connections are made as per the circuit diagram.

ARMATURE CONTROL METHOD:

2. By adjusting the field rheostat, the field current is kept at constant value.

3. Then by varying the armature voltage, the speed is measured.

4. The graph is plotted across the different value of armature voltage and

speed.

FIELD CONTROL METHOD:

1. By adjusting the armature rheostat, the armature voltage is kept at constant

value.

2. Then by varying the field current, the different speeds are tabulated.

3. The procedure is repeated and graph is plotted between field current and

speed.



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MODEL GRAPH FIELD CONTROL METHOD

ARMATURE CONTROL METHOD



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RESULT:



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2. How many types of speed controls are there?

3. By which method we can control the speed of dc shunt motor above rated speed?

4. Explain the armature control method?

5. By which method we can control the speed of dc shunt motor below rated speed ?

6. Explain the field control method?

7. Application of DC shunts motor?

8. If you vary the armature rheostat from minimum to maximum what will happen to

the speed of the motor?

9. If you vary the field rheostat from minimum to maximum position what will

happen to the speed of the motor?

10. What type of starter is used in DC shunt motor?



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LOAD TEST THREE PHASE INDUCTION MOTOR

NAME PLATE DETAILS:



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AIM:

To conduct the load test on 3Φ induction motor and to draw its characteristic

graph.

APPARATUS REQUIRED:

S. No Apparatus Range Quantity

1 Wattmeter 600V/15A UPF 2

2 Voltmeter (0-600V)mi 1

3 Ammeter (0-10)A mi 1

4 Tachometer 1

5 Autotransformer 415V/(0-470V)0.8A 1


FORMULAE USED:

1. Input power = w1+w2 watt

W1 – Power measured in I wattmeter

W2 – Power measured in II wattmeter

2. Torque =(T1 ~ T2)*9.81*r nm

T1~ T2 – difference in weight (kg)

R – The radius of brake drum.

3. Output power = 2πNT/60 watt

N – Speed in rpm

T – Torque in nm

4. % Efficiency = (output power/input power) *100

5. % Slip = (Ns-Nr/Ns) *100

Ns – Synchronous speed of motor in rpm

Ex.No. LOAD TEST ON 3Φ SQUIRREL CAGE INDUCTION MOTOR Date:



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TABULATION:

S.No

VL V

ILA I/P (watts)

W1 (Watts) W2 (watts)

T1 (kg)

T2 (kg)

T1~T2 (kg)

T (Nm)

O/p (w)

N rpm

p.f %η % slip

act div act div



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Nr – Speed of the motor

6.Power factor = (w1+w2)/root 3 VLIL

W1+w2 – i/p power in watt

VL – line voltage in volt

IL – line current in amps

THEORY:

Induction Machines:

Induction motor is one of the most important machines, which is used in

industrial and domestic applications. These induction motors are classified into

different types namely squirrel cage induction motor and slip ring induction motor.

Where the first one is most preferable because of its rugged construction and its

performance characteristics.

Three Phase Induction Motor:

This motor has normal starting torque and adjustable speed so that speed

control can be acheived easily. Its starting torque increases with increase in the value

of rotor resistance . However maximum torque remains constant and it is independant

of the rotor resistance. But slip varies at above said condition.

Normally DOL, star-delta and autotransformer starter are used to start the

motor. This motor may sometime show a tendency to run at very low speed usually

one seventh of its normal speed. This is because of presence of the harmonics in the

sinusoidal flux wave produced by the stator mmf it is called by the name of crawling.

This motor may exhibit a peculiar behaviour in starting for certain relationship

between the numbers of stator slots equal to an integral multiple of rotor slots. The

variations of reluctance as a function of space will be introduced. This inturn creates

as aligning torque stronger than the accelerating torque with consequent failure of

motor start. This phenomenon is known as cogging.



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MODEL CALCULATIONS:



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RESULT:



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2. what are the applications of induction motor?

3. Which type of connection is applied for stator?

4. why we call this motor as squirrel cage induction motor?

5. Which starter is used for 3 phase squirrel cage induction motor?

6. What is the principle of 3 phase squirrel cage induction motor?



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LOAD TEST ON SINGLE PHASE INDUCTION MOTOR

NAME PLATE DETAILS:



Page 46 of 111

AIM:

To conduct the load test on single phase induction motor and to draw its

performance characteristics.

APPARATUS REQUIRED:


1 Ammeter (0-10)A 1

2 Voltmeter (0-300)V 1

3 Wattmeter (300V/10A) 1

4 1Φ Autotransformer (230V/10-270V) varial 1

5 Tachometer 1


FORMULAE USED:


2. Output power= 2πNT/60 watts

3. % efficiency=output/input*100

Where,

O/p is the out power in watts, I/p is the input power in watts

4. % slip=Ns-Nr/N0*100

Where, Ns – Synchronous speed, Nr – Rotor Speed

5. Power factor= W/IL VL

Ex.No. LOAD TEST ON SINGLE PHASE INDUCTION MOTOR Date:



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TABULATION S.No Volt(v) I(A) Power

(watts) Load T

(NM) N rpm

O/P P.f % η % slip T1 T2



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THEORY:

Construction ally this motor is more or less similar to a poly phase

induction motor, except that Its stator is provided with a single phase winding.

A centrifugal switch is used in some type of motor in order to cut out a

winding, used in some type of motor, in order to cut out a winding, used in

some type of motors for starting squirrel cage rotor, when fed from a single

phase only alternating. One which alternates along one phase axis only. Now,

alternating or pulsating flux acting on a stationary squired cage rotor cannot

produce rotation that is why a single phase motor is not self starting.

PROCEDURE:


2. Set the rated voltage in the voltmeter by varying the auto transformer and

note down the no load readings.

3. By increasing the load, note down the various loaded readings.



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MODEL CALCULATION:



Page 50 of 111

RESULT:



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2. Whether single phase induction motor self starting motor?

3.What are the starting methods of single phase induction motor?



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REGULATION OF ALTERNATOR BY EMF AND MMF METHOD



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NAME PLATE DETAILS:



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AIM :

To predetermine the regulation of three phase alternator by EMF and MMF

method.

APPARATUS REQUIRED:

S.NO Name of the

Apparatus Type

Range

Quantity

1

2

3

4

5

6

7

8

9

Ammeter

Ammeter

Ammeter

Ammeter

Voltmeter

Voltmeter

Rheostat

Rheostat

Tachometer

MC

MC

MC

MI

MI

MC

Wire wound

Wire wound

(0-2)A

(0-10)A

(0-5)A

(0-10)A

(0-600)V

(0-150V)

(500,1.2A)

(300,1.7A)

1

1

1

1

1

1

1

1

1

PRECAUTION:

The motor field rheostat should be kept at the minimum

resistance position while starting.

The Alternator field Potential divider should be in the

maximum voltage position.

Initially all switches are in open position.

Ex.No. REGULATION OF THREE PHASE ALTERNATOR BY EMF AND MMF METHODS Date:



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TABULATION :

OPEN CIRCUIT TEST:

S.NO Field current (If)

Open circuit

Voltage (V)

Open circuit Phase

voltage (Vo(ph))

Amps Volts volts

SHORT CIRCUIT TEST :

S.NO Field current (If)

Short circuit current (120 to 150% of

rated current) (Isc)

Amps Amps

TO FIND THE ARMATURE RESISTANCE(Ra)

S.NO

Armature current

(Ia)

Armature voltage

(Va)

Armature resistance

Ra = Va /Ia

Amps Volts Ohms

Average value of Ra =



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PROCEDURE FOR BOTH EMF AND MMF METHOD:

Connections are given as per the circuit diagram.

The supply is given by closing the DPST switch.

The motor is started to run at its rated speed by varying the motor field

rheostat.

The open circuit test is conducted by varying the potential divider for

various values of field current and all the meter readings are noted

down.

By closing the TPST switch the short circuit test is conducted with the

rated armature current which has been set by adjusting the potential

divider and corresponding field current is noted down.

By giving connection as per the circuit diagram for stator resistance

test the stator windings is loaded gradually and all the meter readings

are noted down for different values of load.

The supply is switched off after bringing the load gradually to its initial

position.

FORMULAE USED:

EMF METHOD :

1. Armature resistance,Ra = 1.6Rdc

Rdc is the resistance in the DC supply

2. Synchronous impedence,Zs = open circuit voltage (E1(ph)) / short circuit

current (Isc)

3. Synchronous reactance,Xs = )( 22 RaZs

4. Open circuit voltage,Eo = 22 rated IaXs) sin rated (V IaRa) cos(V

(For lagging power factor)

5. Open circuit voltage, Eo = 22 IaXs) - sin rated (V IaRa) cos (Vrated

(For leading power factor)

6. Open circu it voltage, Eo = 22 (IaXs) IaRa) (Vrated

(For unity power factor)

7. Percentage regulation= )(100* methodsandMMFForbothEMFV

VratedEorated



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RESULTANT TABULATION FOR REGULATION THREE PHASE

ALTERNATOR BY EMF AND MMF METHODS

S.No

PERCENTAGE OF REGULATION

Power factor

EMF method MMF Method Vector Diagram

Lagging Leading Unity Lagging Leading Unity Lagging Lead

ing Unity

1 0.2 - - -

2 0.4 - - -

3 0.6 - - -

4 0.8 - - -

5 1.0 - - -



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THEORY:

EMF METHOD

This method is otherwise called Behn Eschenberg method or pessimistic

method. In this method armature reaction is treated as additional voltage drop by

introduction of a fictitious reactance called armature reaction reactance ,Xa i.e., the

reaction is replaced by reactance. Under short circuit test a small amount of field

current is necessary to circulate the full load current through the windings. The

induced Emf corresponding to this excitation is more under actual load. Hence this

method is called pessimistic method.

MMF METHOD

This method is otherwise called as Ampere turns method or optimistic method.

In this method leakage reactance is treated as additional reaction. The regualtion

determined by this method is less than the actual value. The field current taken from

the short circuit characteristics refers to unsaturated condition. But under normal load

the magnetic circuit is saturated and the mmf required for leakage drop is much more.

Therefore regulation calculated by mmf method is less.



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MODEL CALCULATION:



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PROCEDURE TO DRAW THE GRAPH FOR EMF METHOD:

Draw the open circuit characteristics curve (Generated voltage per phase

Vs Field current)

Draw the short circuit characteristics curve (Short circuit current Vs Field

current)

From the graph find the open circuit voltage per phase (E1(ph)) for the

rated short circuit current (Isc).

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

regulation.

PROCEDURE TO DRAW THE GRAPH FOR MMF METHOD:

Draw the open circuit characteristics curve (Generated voltage per phase Vs

Field current)

Draw the short circuit characteristics curve (Short circuit current Vs Field

current)

Draw the line OL to represent Ir′ which gives the rated generated voltage

(V).

Draw the line LA at an angle (90º±ф) to represent Ir′′ which gives the

rated full load

current (Isc) on short circuit [(90 + ф) for lagging power factor and (90 -

ф) for leading

power factor ].

Join the points O and A and find the field current ( If by measuring the

distance OA

that gives the open circuit voltage (Eo) from the open circuit

characteristics.

Find the percentage regulation by using suitable formula.



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RESULT:



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DISCUSSION QUESTIONS: 1. Full form of EMF?

2. Full form of MMF?


4. In which machine this experiment is performed?

5. What is meant by alternator?

6. What is meant by voltage regulation?

7. In which field current is greater, open circuit or short circuit?

8. In which regulation is greater, EMF method or MMF method?

9. What is meant by unity power factor?



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V AND INVERTED V CURVES OF THREE PHASE SYNDHRONOUS MOTOR

NAME PLATE DETAILS:



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AIM:

To draw the V and inverted V curves of three phase synchronous motor.

APPARATUS REQUIRED :

S.NO Name of the Apparatus Type Range Quantity

1

2

3

4

5

6

Ammeter

Ammeter

Voltmeter

Power factor meter

Rheostat

Tachometer

MC

MI

MI

Double element

Wire wound

(0-2)A

(0-10)A

(0-600)V

(500V,10A)

(500,1.2A)

1

1

1

1

1

1

FORMULAE USED:

Cos ф=Ia(min)/Ia

THEORY:

V curve and Inverted V curve of synchronous motor:

Synchronous motor is constant speed motor, which are not self starting in

nature. So that we have to start this motor by any one of the following starting

methods,

1. Pony motor method starting

2. DC exciter starting

3. Auto induction start (or) Damper winding method of starting

By construction there is no difference between synchronous generator and

synchornous motor. It is capable of being operated under wide range of power factor

hence it can be used for power factor correction.

4. The value of excitaiton for which back EMF is equal to applied voltage

is known as 100% excitation. The other two possible excitations are

over excitation and under excitation if the back emf is more or less to

the applied voltage respectively

Ex.No. V AND INVERTED V CURVES OFTHREE PHASE SYNCHRONOUS MOTOR Date:



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TABULATION: Armature voltage:

S.No

Without Load With load(1/4) With load (1/2)

Excitation

current

(If)

Armature

current

(Ia)

Power

factor.

(cos

ф)

Excitation

current

(If)

Armature

current

(Ia)

Power

factor.

(cos

ф)

Excitation

current

(If)

Armature

current

(Ia)

Power

factor.

(cos

ф)

Amps Amps Amps Amps Amps Amps



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PRECAUTION:

1. connections are made as per circuit diagram

2. At initial condition, the field rheostat is kept at maximum position.

3. set the voltage at 150V by varying the auto transformer, such that the load

current is greater than the rated current (DPST open)

4. The DC supply is given to field winding by closing DPST switch (the load

current decreases)

5. Then open the DPST switch and set rated amps (7 amps) by varying auto

transformer, close (DPSTS)

6. Note the Ammeter value, The field rheostat is varied (max to min), the load

current decreases and at one point the load current increases up to initial value

note the ammeter readings

7. Apply load, till ½ load (3.5 amps) and repeat step 6 note the readings. For ¾

load (Apply load till ¾ load (5.2 amps) and repeat step 6 note the readings)

8. Release the load, bring rheostat position to maximum condition, open DPST

switch and switch off the power supply.



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MODEL CALCULATION:



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RESULT:



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1. In which motor we perform this experiment?

2. What is the speed nature of 3-phase synchronous motor?

3. What is the propose of this experiment?

4. What is the characteristic of v curve?

5. What is the characteristic of Λ curve?

6. What are the different range of loads used in this experiment?

7. How will you apply load in this experiment?

8. Application of synchronous motor?

9. What is the armature current nature when load is applied in V curve?

10. What is the field current nature when load is applied in Λ curve?



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Page 75 of 111

LOAD TEST ON SINGLE PHASE TRANSFORMER

NAME PLATE DETAILS:



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AIM:

To conduct a load test on a single-phase transformer to determine the

efficiency and regulation of single-phase transformer.

APPARATUS REQUIRED:


1 Voltmeter (0-300V)MI 1

(0-150V)MI 1

2 Ammeter (0-5A)MI 1

(0-10A)MI 1

3 Autotransformer 230V/(0-270)V8A 1

4 Load rheostat 230V/2-5KW 1

5 Wattmeter 300V/10A(UPF) 1

150V/20A(LPF) 1

6 Transformer Step down 230:115 1

7 Connecting wire

FORMULAE USED:

i) % Efficiency =w2/w1*100

ii) % Regulation up = V02-V2/V2*100

iii) % Regulation down= V02-V2/V02*100

Where

V02- Secondary terminal voltage at no load condition

V2- Secondary terminal voltage at load condition

W1- Wattmeter reading at primary side.

W2- Wattmeter reading at secondary side.

Ex.No. LOAD TEST ON SINGLE –PHASE TRANSFORMER Date:



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TABULATION: S.No VL IL W1 (watts) VL IL W2 (watts) % η % reg

up % reg down observed Actual observed Actual

MODEL GRAPH



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THEORY

A transformer is a device by means of which electric power can be

transformed from one circuit to another circuit without change in frequency either by

step up or step down the voltage. The transformer works on the principle of mutual

induction if the coil is connected in a source or alternating voltage a flux is step up on

laminated core most of which it is linked mutually induced emf of the coil where AC

supply is fed is called primary winding and from which the energy is drawn out is

called secondary winding.

PROCEDURE:

i) Connections are made as per the circuit diagram.

ii) By varying the autotransformer set the rated voltage on the primary

side.

iii) At on load condition the input and output voltage current and power

are noted.

iv) As the load is measured is step-by-step using a load rheostat take all

the input, output reading up to the rated current.



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MODEL CALCULATION:



Page 80 of 111

RESULT:



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1. What is the other name of single phase transformer?


3. What is the application of single phase transformer?

4. What is the principle of transformer?

5. What is the relationship between efficiency and load?

6. What is the relation between load and regulation?

7. Which type of load is used in this experiment?

8. Relationship between load & output power?

9. How will you set the primary winding voltage?

10. What will be the efficiency at zero load?



Page 82 of 111



Page 83 of 111

OC TEST ON SINGLE PHASE TRANSFORMER

NAME PLATE DETIALS:



Page 84 of 111

AIM:

To conduct the Oc test and Sc test on single phase transformer and to

draw the equivalent Circuit diagram

APPARATUS REQUIRED:

FORMULAE USED:

1. OC Test

W0=V0I0 cos Φ0

Iw= I0 cos Φ0

Iµ= I0 sin Φ0

R0=V0/Iw

X0=V0/ Iµ Where, W0_-no load power I0 -no load current V0 -no load voltage Iw -working current component Iµ -Magnetizing current component R0 - circuit resistance X0 - circuit reactance Cos Φ0-PF between no load current and voltage

Ex.No. OPEN CIRCUIT AND SHORT CIRCUIT TEST ON SINGLE PHASE TRANSFORMER Date:


1 1Φ Auto transformer 230V/(0-270V)8A 1

2 Voltmeter (0-150V)MI 1

(0-300V)MI 1

3 Ammeter (0-2A)MI 1

(0-5A)MI 1

4 Wattmeter 300V/5A UPF 1

300V/5A LPF 1

5 Step down transformer 230/115V 1



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SC TEST ON SINGLE PHASE TRANSFORMER

NAME PLATE DETIALS:



Page 86 of 111

2. SC Test

Wsc=Vsc Isc cos Φsc

R01=Vsc/Isc2

Z01=Vsc/Isc

X01= square root of Za2-Ra

2

Where

Wsc= Short circuit power

Vsc =Short circuit voltage

Isc=Short circuit current

R01=Total effective resistance

Z01=total effective impedance

X01=total effective reactance

% Regulation

1) % lagging power factor= Isc [R01 cos Φ0+X01 sin Φ0]*100/V0

2) % leading power factor= Isc [R01 cos Φ0-X01 sin Φ0]*100/V0

3) Efficiency=x*KVA*PF/[x*KVA*PF]+W0+x2 Vsc



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TABULATION: S.No Vo(V) Io(A) Wo

div Actual(mf= )

S.No Vsc(V) Isc(A) Wsc

div Actual(mf= )

S.No cosΦ sinΦ % of

lagging regulation

p.f

% of lagging

regulation p.f

Efficiency η

X=0.25 X=0.5 X=0.75 X=1



Page 88 of 111

THEORY:

Open circuit test:

The purpose of this test is to determine no load loss or core

loss and no load current I0 which is helpful one winding in open circuited and a

voltage usually noted voltage at rated frequency is applied to the other winding

the voltage power and current terminals of this are measured with normal voltage

applied to the primary normal flux will setup in the core hence normal iron loss

will occur which will be recorded in the wattmeter. As the primary and nill in the

secondary. Hence the wattmeter reading represents practically under no load

condition.

Short Circuit test:

In this test one winding is short circuited across its terminals

and reduced voltage is applied to the other winding. A low winding voltage at

correct frequency is applied to the primary and its continuously increases till full

load and flux in the primary and secondary since in this test the primary and

secondary percentage at normal flux is produced. It is also a small percentage of

the normal voltage hence core losses are very small with the result that the

wattmeter reading represents the full load copper losses or I2R loss in the whose

transformed. We also obtain the equivalent circuit transformer under short-

circuited condition.

PROCEDURE:


2. The autotransformer is varied up to rated voltage. Note the no load reading

from which the

equivalent circuit impedance parameter. R0 and X0 are calculated.

3. The SC readings are noted from the sc test from which the equivalent circuit

parameter X0

and R0 are determined.



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MODEL GRAPH EQUIVALENT CIRCUIT:



Page 90 of 111

MODEL CALCULATION:



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Page 94 of 111

RESULT:



Page 95 of 111

DISCUSSION QUESTUIONS:

1. Write the purpose of this experiment?

2. What are the main parameters of the equivalent circuit?

3. What is the other name of O.C Test?

4. What is the other name of S.C Test?

5. What is the purpose of O.C Test?

6. What is the purpose of S.C Test?

7. Why transformer power rating is in KVA?



Page 96 of 111



Page 97 of 111

SPEED CONTROL OF 3Ф SLIP RING INDUCTION MOTOR

NAME PLATE DETAILS:



Page 98 of 111

AIM:

To Conduct the experiment for the speed control of 3Ф slip ring induction

motor by Stator Voltage Control

APPARATUS REQUIRED:

THEORY:

The slip ring or wound rotor motor is an induction machine where

the rotor comprises a set of coils that are terminated in slip rings. These are metal

rings rigidly mounted on the rotor, and combined with brushes (as used with

commutators), provide continuous unswitched connection to the rotor windings.

In the case of the wound-rotor induction motor, external

impedances can be connected to the brushes. The stator is the same as is used with a

standard squirrel cage motor. By changing the impedance connected to the rotor

circuit, the speed/current and speed/torque curves can be altered.(Slip rings are also

often used in alternators as well as in synchro angular data-transmission devices,

among other applications.) The slip ring motor is used primarily to start a high inertia

load or a load that requires a very high starting torque across the full speed range. By

correctly selecting the resistors used in the secondary resistance or slip ring starter, the

motor is able to produce maximum torque at a relatively low supply current from zero

speed to full speed. This type of motor also offers controllable speed.

Ex.No. SPEED CONTROL OF 3Ф SLIP RING INDUCTION MOTOR Date:

S.No Apparatus Range Quantity 1 Voltmeter (0-600V)MI 1 2 Tachometer Digital/Analog 1 3 3Ф Auto transformer - 1

4 Connecting Wires Few



Page 99 of 111

TABULATION:

S.No Voltage(volts) Speed(rpm)

MODEL GRAPH



Page 100 of 111

Motor speed can be changed because the torque curve of the motor is

effectively modified by the amount of resistance connected to the rotor circuit.

Increasing the value of resistance will move the speed of maximum torque down. If

the resistance connected to the rotor is increased beyond the point where the

maximum torque occurs at zero speed, the torque will be further reduced. When used

with a load that has a torque curve that increases with speed, the motor will operate at

the speed where the torque developed by the motor is equal to the load torque.

Reducing the load will cause the motor to speed up, and increasing the load will cause

the motor to slow down until the load and motor torque are equal. Operated in this

manner, the slip losses are dissipated in the secondary resistors and can be very

significant. The speed regulation is also very poor.

PROCEDURE:

1. Connections are given as per the circuit diagram

2. Keep the 3Ф autotransformer in minimum position and switch ON the power

supply.

3. Start the 3Ф sip ring induction motor by using auto transformer

4. By varying the auto transformer and change the voltage then the speed of the motor

can be controlled.

RESULT:



Page 101 of 111



2. Other name of induction motor?

3. What type of starter is used in induction motor?

4. Which type of connection is applied for stator?

5. Which type of connection is applied for rotor?

6. Relation between voltage and speed?

7. How can the direction of rotation can be revered?

8. Define slip?

9. Does the starter is required for induction motor?

10. Application of induction motor.

11. What is the nature of torque in induction motor?



Page 102 of 111



Page 103 of 111



Page 104 of 111

Three point starter

A “3-point starter” is extensively used to start a D.C shunt motor. It not only

overcomes the difficulty of a plain resistance starter, but also provides additional

protective features such as over load protection and no volt protection. The diagram of

a 3-point starter connected to a shunt motor is shown in figure. Although, the circuit

looks a bit clumsy at a first glance, the basic working principle is same as that of plain

resistance starter The starter is shown enclosed within the dotted rectangular box

having three terminals marked as A, L and F for external connections. Terminal A is

connected to one armature terminal Al of the motor. Terminal F is connected to one

field terminal F1 of the motor and terminal L is connected to one supply terminal as

shown. F2 terminal of field coil is connected to A2 through an external variable field

resistance and the common point connected to supply (-ve). The external armatures

resistances consist of several resistances connected in series and are shown in the

form of an arc. The junctions of the resistances are brought out as terminals (called

studs) and marked as 1, 2,.. .12. Just beneath the resistances, a continuous copper strip

also in the form of an arc is present. There is a handle which can be moved in the

clockwise direction against the spring tension. The spring tension keeps the handle in

the OFF position when no one attempts to move it. Now let us trace the circuit from

terminal L (supply + ve). The wire from L passes through a small electro magnet

called OLRC, (the function of which we shall discuss a little later) and enters through

the handle shown by dashed lines. Near the end of the handle two copper strips are

firmly connected with the wire. The furthest strip is shown circular shaped and the

other strip is shown to be rectangular. When the handle is moved to the right, the

circular strip of the handle will make contacts with resistance terminals 1, 2 etc.

progressively. On the other hand, the rectangular strip will make contact with the

continuous arc copper strip. The other end of this strip is brought as terminal F after

going through an electromagnet coil (called NVRC). Terminal F is finally connected

to motor field terminal Fl.

Ex.No. STUDY OF DC AND AC STARTERS Date:



Page 105 of 111



Page 106 of 111

Working principle

Let us explain the operation of the starter. Initially the handle is in the OFF

position. Neither armature nor the field of the motor gets supply. Now the handle is

moved to stud number 1. In this position armature and all the resistances in series gets

connected to the supply. Field coil gets full supply as the rectangular strip makes

contact with arc copper strip. As the machine picks up speed handle is moved further r

to stud number 2. In this position the external resistance in the armature circuit is less

as the first resistance is left out.All resistances will be left out when stud number 12

(ON) is reached. In this position, the electromagnet (NVRC) will attract the soft iron

piece attached to the handle. Even if the operator removes his hand from the handle, it

will still remain in the ON position as spring restoring force will be balanced by the

force of attraction between NVRC and the soft iron piece of the handle. The no volt

release coil (NVRC) carries same current as that of the field coil. In case supply

voltage goes off, field coil current will decrease to zero. Hence NVRC will be

deenergised and will not be able to exert any force on the soft iron piece of the handle.

Restoring force of the spring will bring the handle back in the OFF position.

The starter also provides over load protection for the motor. The other

electromagnet, OLRC overload release coil along with a soft iron piece kept under it,

is used to achieve this. The current flowing through OLRC is the line current IL

drawn by the motor. As the motor is loaded, Ia hence IL increases. Therefore, IL is a

measure of loading of the motor. Suppose we want that the motor should not be over

loaded beyond rated current. Now gap between the electromagnet and the soft iron

piece is so adjusted that for the iron piece will not be pulled up.

However, if rated I I force of attraction will be sufficient to pull up iron

piece. This upward movement of the iron piece of OLRC is utilized to de-energize

NVRC. To the iron a copper strip (Ä shaped in figure) is attached. During over

loading condition, this copper strip will also move up and put a short circuit between

two terminals B and C. Carefully note that B and C are nothing but the two ends of

the NVRC. In other words, when over load occurs a short circuit path is created

across the NVRC. Hence NVRC will not carry any current now and gets reenergized.



Page 107 of 111

Direct on-line starter



Page 108 of 111

The moment it gets deenergised, spring action will bring the handle in the OFF

position thereby disconnecting the motor from the supply. Three-point starter has one

disadvantage. If we want to run the machine at higher speed (above rated speed) by

field weakening (i.e., by reducing field current), the strength of NVRC magnet may

become so weak that it will fail to hold the handle in the ON position and the spring

action will bring it back in the OFF position. Thus we find that a false disconnection

of the motor takes place even when there is neither over load nor any sudden

disruption of supply.

In electrical engineering, a direct on line (DOL) or across the line starter

starts electric motors by applying the full line voltage to the motor terminals. This is

the simplest type of motor starter. A DOL motor starter also contain protection

devices, and in some cases, condition monitoring.

A direct on line starter can be used if the high inrush current of the motor does

not cause excessive voltage drop in the supply circuit. The maximum size of a motor

allowed on a direct on line starter may be limited by the supply utility for this reason.

For example, a utility may require rural customers to use reduced-voltage starters for

motors larger than 10 kW.DOL starting is sometimes used to start small water pumps,

compressors, fans and conveyor belts. In the case of an asynchronous motor, such as

the 3-phase squirrel-cage motor, the motor will draw a high starting current until it

has run up to full speed. This starting current is commonly around six times the full

load current, but may as high as 12 times the full load current. To reduce the inrush

current, larger motors will have reduced-voltage starters or variable speed drives in

order to minimise voltage dips to the power supply.

DOL reversing starter

A reversing starter can connect the motor for rotation in either direction. Such

a starter contains two DOL circuits—one for clockwise operation and the other for

counter-clockwise operation, with mechanical and electrical interlocks to prevent

simultaneous closure.[1] For three phase motors, this is achieved by transposing

anytwo phases. Single phase AC motors and direct-current motors require additional

devices for reversing rotation.



Page 109 of 111



Page 110 of 111

Overload relays

A starter will contain protective devices for the motor. At a minimum this

would include a thermal overload relay. The thermal overload is designed to open the

starting circuit and thus cut the power to the motor in the event of the motor drawing

too much current from the supply for an extended time. The overload relay has a

normally closed contact which opens due to heat generated by excessive current

flowing through the circuit. Thermal overloads have a small heating device that

increases in temperature as the motor running current increases.There are two types of

thermal overload relay. In one type, a bi-metallic strip located close to a heater

deflects as the heater temperature rises until it mechanically causes the device to trip

and open the circuit, cutting power to the motor should it become overloaded. A

thermal overload will accommodate the brief high starting current of a motor while

accurately protecting it from a running current overload. The heater coil and the

action of the bi-metallic strip introduce a time delay that affords the motor time to

start and settle into normal running current without the thermal overload tripping.

Thermal overloads can be manually or automatically resettable depending on their

application and have an adjuster that allows them to be accurately set to the motor run

current.

Loss of voltage protection

Starters using magnetic contactors usually derive teh poer supply for the

contactor coil from the same source as the motor supply. An auxiliary contact from

the contactor is used to maintain the contactor coil energized after the start command

for the motor has been released. If a momentary loss of supply voltage occurs, the

contactor will open and not close again until a new start command is given. this

prevents restarting of the motor after a power failure. This connection also provides a

small degree of protection against low power supply voltage and loss of a phase.

However since contactor coils will hold the circuit closed with as little as 80% of

normal voltage applied to the coil, this is not a primary means of protecting motors

from low voltage operation.

RESULT:



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Documents

ME 39-Electrical Engineering Lab Manual