valliammai engineering college semester/ee6365... · speed control of dc shunt motor (armature, ......

VALLIAMMAI ENGINEERING COLLEGE

MECHANICAL ENGINEERING

II YEAR / III SEMESTER

EE 6365 - Electrical Engineering Laboratory

(RLEGULATION - 2013)

Academic Year: 2017-2018 (Odd Semester)

Prepared By : 1. Dr.MALATHI.S, A.P (Sr.G) / EEE

2. TAMILARASAN.P, A.P (O.G) / EEE

3. ELAVARASI.R, A.P (O.G) / EEE


EE 6365 -- ELECTRICAL ENGINEERING LABORATORY

LIST OF EXPERIMENTS

1. Load test on DC Shunt & DC Series motor

2. O.C.C & Load characteristics of DC Shunt and DC Series generator

3. Speed control of DC shunt motor (Armature, Field control)

4. Load test on single phase transformer

5. O.C & S.C Test on a single phase transformer

6. Regulation of an alternator by EMF & MMF methods.

7. V curves and inverted V curves of synchronous Motor

8. Load test on three phase squirrel cage Induction motor

9. Speed control of three phase slip ring Induction Motor

10. Load test on single phase Induction Motor.

11. Study of DC & AC Starters

ADDITIONAL EXPERIMENTS:

1. Load test on DC Compound motor

2. Swinburne's Test

1


CYCLE I:

1. Load test on DC Shunt motor

2. Load test on DC Series motor

3. O.C.C & Load characteristics of Self Excited DC Shunt generator

4. O.C.C & Load characteristics of Separately Excited DC Shunt

generator

5. O.C.C & Load characteristics of DC Series generator

6. Speed control of DC shunt motor (Armature, Field control)

7. Load test on single phase transformer

8. O.C & S.C Test on a single phase transformer

CYCLE II:

9. Regulation of an alternator by EMF method.

10. Regulation of an alternator by MMF method.

11. Load test on single phase Induction Motor.

12. Load test on three phase squirrel cage Induction motor

13. Speed control of three phase slip ring Induction Motor

14. V curves and inverted V curves of synchronous Motor

15. Study of DC & AC Starters

2


S.No

Date

Name of the Experiment

Marks

Signature

3


LOAD TEST ON DC SHUNT MOTOR

4


Ex.No.1

AIM:

LOAD TEST ON DC SHUNT MOTOR

To conduct load test on DC shunt motor and to find efficiency.

APPARATUS REQUIRED:

S.No.

Apparatus

Range

Type

Quantity

1

Ammeter

(0-20)A

MC

1

2

Voltmeter

(0-300)V

MC

1

3

Rheostat

500 ohm, 2A

Wire W ound

1

4

Tachometer

(0-1500) rpm

Digital

1

5

Connecting W ires

2.5sq.mm.

Copper

Few

PRECAUTIONS:

1. DC shunt motor should be started and stopped under no load condition.

2. Field rheostat should be kept in the minimum position.

3. Brake drum should be cooled with water when it is under load.

PROCEDURE:

1. Connections are made as per the circuit diagram.

2. After checking the no load condition, and minimum field rheostat position, DPST

switch is closed and starter resistance is gradually removed.

3. The motor is brought to its rated speed by adjusting the field rheostat.

4. Ammeter, Voltmeter readings, speed and spring balance readings are noted

under no load condition.

5. The load is then added to the motor gradually and for each load, voltmeter,

ammeter, spring balance readings and speed of the motor are noted.

6. The motor is then brought to no load condition and field rheostat to minimum

position, then DPST switch is opened.

5


Spee

d N

(rpm

)

TABULAR COLUMN:

S.No.

Voltage

V

(Volts)

Current

I

(Amps)

Spring

Balance

Reading

(S1 S2)

Kg

Speed

N

(rpm)

Torque

T

(Nm)

Output

Power

Pm

(Watts)

Input

Power

Pi

(Watts)

Efficiency

%

S1(Kg) S2(Kg)

Circumference of the Brake drum = …………..cm.

MODEL GRAPHS:

y

x

Torque T (Nm)

6


VIVA QUESTIONS:

1. State the necessity of starter.

2. State the principle of DC motor.

3. How will you reverse the direction of rotation of DC motor?

4. W hy the field rheostat of DC motor is kept at minimum position while starting?

RESULT:

Thus load test on DC shunt motor is conducted and its efficiency is determined.

7


LOAD TEST ON DC SERIES MOTOR

8


Ex.No.2

AIM:

LOAD TEST ON DC SERIES MOTOR

To conduct load test on DC Series Motor and to find efficiency.

APPARATUS REQUIRED:

S.No. Apparatus Range Type Quantity

1 Ammeter (0-20)A MC 1

2 Voltmeter (0-300)V MC 1

3 Tachometer

(0-3000)

rpm

Digital

1

4 Connecting W ires 2.5sq.mm. Copper Few

PRECAUTIONS:

1. The motor should be started and stopped with load


PROCEDURE:


2. After checking the load condition, DPST switch is closed and starter resistance is

gradually removed.

3. For various loads, Voltmeter, Ammeter readings, speed and spring balance

readings are noted.

4. After bringing the load to initial position, DPST switch is opened.

9

Effic

ienc

y %

Torq

ue T

(Nm

)

Spee

d N

(rpm

)


TABULAR COLUMN:

S.No.

Voltage

V

(Volts)

Current

I

(Amps)

Spring

Balance

Reading

(S1 S2)

Kg

Speed

N

(rpm)

Torque

T

(Nm)

Output

Power

Pm

(Watts)

Input

Power

Pi

(Watts)

Efficiency

%

S1(Kg) S2(Kg)


MODEL GRAPH:

y3 y2 y1

T

E

N

Output Power (Watts)

VIVA QUESTIONS:

1. DC series motors should never be started on no-load. W hy?

2. W hy the DC series motors have high starting torque?

3. W hat are the applications of DC series motors?

4. W hich type of starter is used for DC series motors?

5. How will you control the speed of DC series motor?

RESULT:

Thus load test on DC series motor is conducted and its efficiency is determined.

11


12


Ex.No.3 (a) OPEN CIRCUIT CHARACTERISTICS OF SELF EXCITED

DC SHUNT GENERATOR

AIM:

To obtain open circuit characteristics of self-excited DC shunt generator and to

find its critical resistance.

APPARATUS REQUIRED:

S.No.

Apparatus

Range

Type

Quantity

1

Ammeter

(0-2)A

MC

1

2

Voltmeter

(0-300)V

MC

1

3

Rheostats

1000 ohm,0.8 A,

500 ohm , 3A

Wire W ound

1 each

4

SPST Switch

-

-

1

5

Tachometer

(0-1500)rpm

Digital

1

6

Connecting W ires

2.5sq.mm.

Copper

Few

PRECAUTIONS:

1. The field rheostat of motor should be in minimum resistance position at the time

of starting and stopping the machine.

2. The field rheostat of generator should be in maximum resistance position at the

time of starting and stopping the machine.

3. DPST switch is kept open during starting and stopping.

PROCEDURE:


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

generator field rheostat, DPST switch is closed and starting resistance is

gradually removed.

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

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

13


E o (V

olts

)

TABULAR COLUMN:

S.No.

Field Current

If (Amps)

Armature Voltage

Eo (Volts)

MODEL GRAPH:

Critical Resistance = Eo / If Ohms

If

Eo

If (Amps)

14


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

and ammeter readings are taken.

6. After bringing the generator rheostat to maximum position, field rheostat of motor

to minimum position, SPST switch is opened and DPST switch is opened.

VIVA QUESTIONS:

1. Define the term critical resistance referred to DC shunt generator.

2. W hat do you mean by residual magnetism in DC shunt generators?

3. W hat is the principle of DC generator?

4. Define the term critical speed in DC shunt generator

5. Mention the application of separately excited DC generator

RESULT:

Thus open circuit characteristics of self excited DC shunt generator are obtained

and its critical resistance is determined.

15


16


Ex. No: 3(b)

AIM:

LOAD CHARACTERISTICS OF SELF EXCITED

DC SHUNT GENERATOR

To obtain internal and external characteristics of DC shunt generator.

APPARATUS REQUIRED:


1 Ammeter

(0-2)A

(0-20) A MC

MC 1

1


3 Rheostats 1000 ohm, 0.8A

500 ohm, 2A

Wire W ound

1 Each

4 Loading Rheostat 5KW , 230V - 1

5 Tachometer (0-1500)rpm Digital 1


PRECAUTIONS:

1. The field rheostat of motor should be at minimum position.

2. The field rheostat of generator should be at maximum position.

3. No load should be connected to generator at the time of starting and stopping.

PROCEDURE:


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

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

resistance is gradually removed.

17


DETERMINATION OF ARMATURE RESISTANCE:

TABULAR COLUMN:

S.No. Voltage

V (Volts) Current

I (Amps) Armature Resistance

Ra (Ohms)

TABULAR COLUMN:

S.N

o.

Field

Current

If (Amps)

Load

Current

IL (Amps)

Terminal

Voltage

(V) Volts

Ia = IL + If

(Amps)

Eg =V + Ia Ra

(Volts)

18


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

bringing the voltage to rated voltage by adjusting the field rheostat of generator.

4. Load is varied gradually and for each load, voltmeter and ammeter readings are

noted.

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

brought to maximum position and the field rheostat of DC shunt motor to

minimum position, DPST switch is opened.

PROCEDURE TO FIND OUT ARMATURE RESSISTANCE:


2. Supply is given by closing the DPST switch.

3. Readings of Ammeter and Voltmeter are noted.

4. Armature resistance in Ohms is calculated as Ra = (Vx1.5) /I

FORMULAE:

Eg =

Ia =

Eg :

V :

Ia :

IL :

If :

V + Ia Ra (Volts) IL + If

(Amps) Generated emf

in Volts

Terminal Voltage in Volts

Armature Current in Amps

Line Current in Amps

Field Current in Amps

Ra : Armature Resistance in Ohms

19

VL,

E (V

olts

)


MODEL GRAPH:

E Vs IL

(Int Char)

V Vs IL

(Ext Char)

If, IL (Amps)

20


VIVA QUESTIONS:

1. W hat will be the value of current in open circuit condition?

2. W hat is mean by armature reaction?

3. W hat are the causes of failure of excitation in dc generators?

4. W hy shunt generator characteristics turns back when overloaded?

RESULT:

Thus the load characteristics of self excited DC shunt generator is obtained.

21


22


Ex.No:3(c)

OPEN CIRCUIT CHARACTERISTICS OF SEPARATELY EXCITED DC SHUNT GENERATOR

AIM:

To obtain open circuit characteristics of separately excited DC shunt generator.

APPARATUS REQUIRED:

S.No.

Apparatus

Range

Type

Quantity

1

Ammeter

(0-2)A

MC

1

2

Voltmeter

(0-300)V

MC

1

3

Rheostats

500 ohm,, 2A, 250 ohm ,1.5A

Wire W ound

1 Each

4

Tachometer

(0-1500)rpm

Digital

1

5

Connecting W ires

2.5sq.mm.

Copper

Few

PRECAUTIONS:

1. The field rheostat of motor should be in minimum resistance position at the time

of starting and stopping the machine.

2. The field rheostat of generator should be in maximum resistance position at the

time of starting and stopping the machine.

PROCEDURE:


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

generator field rheostat, DPST switch is closed and starting resistance is

gradually removed.

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

4. By varying the generator field rheostat, voltmeter and ammeter readings are

taken.

5. After bringing the generator rheostat to maximum position, field rheostat of motor

to minimum position, DPST switch is opened.

23


E o (V

olts

)

TABULAR COLUMN:

S.No.

Field Current

If (Amps) Armature Voltage

Eo (Volts)

MODEL GRAPH:

If (Amps)

24


RESULT:

Thus open circuit characteristics of separately excited DC shunt generator is

obtained.

25


26


Ex.No:3(d) LOAD CHARACTERISTICS OF SEPARATELY EXCITED

DC SHUNT GENERATOR

AIM: To obtain internal and external characteristics of DC separately excited DC shunt

generator.

APPARATUS REQUIRED:


1 Ammeter

(0-2)A

(0-20) A MC

MC 1

1


3 Rheostatsb 500 ohm , 2A, 250 ohm,1.5A

Wire W ound

1 Each

4 Loading Rheostat 5KW , 230V - 1

5 Tachometer (0-1500)rpm Digital 1


PRECAUTIONS:


2. The field rheostat of generator should be at maximum position.


PROCEDURE:


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

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

resistance is gradually removed.


bringing the voltage to rated voltage by adjusting the field rheostat of generator.

4. Load is varied gradually and for each load, voltmeter and ammeter readings are

noted.

27


DETERMINATION OF ARMATURE RESISTANCE:

TABULAR COLUMN:

S.No. Voltage

V (Volts) Current

I (Amps) Armature Resistance

Ra (Ohms)

TABULAR COLUMN:

S.No. Field

Current

If (Amps)

Load

Current

IL (Amps)

Terminal Voltage

(V) Volts

Ia = IL + If

(Amps)

Eg =V + Ia Ra

(Volts)

28


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

brought to maximum position and the field rheostat of DC shunt motor to

minimum position, DPST switch is opened

PROCEDURE TO FIND ARMATURE RESISTANCE:


2. Supply is given by closing the DPST switch.

3. Readings of Ammeter and Voltmeter are noted.

4. Armature resistance in Ohms is calculated as Ra = (Vx1.5) /I

FORMULAE:

Eg =

Ia =

Eg :

V :

Ia :

IL :

If :

Ra :

V + Ia Ra (Volts) IL + If

(Amps) Generated emf

in Volts

Terminal Voltage in Volts

Armature Current in Amps

Line Current in Amps

Field Current in Amps

Armature Resistance in Ohms

29

VL,

E (V

olts

)


MODEL GRAPH:

E Vs IL

(Int Char)

V Vs IL

(Ext Char)

If, IL (Amps)

30


RESULT:

Thus load characteristics of separately excited DC shunt generator is obtained.

31


32


Ex.No: 4

LOAD CHARACTERISTICS OF DC SERIES GENERATOR

AIM: To obtain the load characteristics of DC series generator.

APPARATUS REQUIRED:

S.No.

Apparatus

Range

Type

Quantity

1

Ammeter

(0-20) A

MC

2

Voltmeter

(0-300)V

MC

1

3

Rheostat

500 ohm , 3A

Wire W ound

1

4

Loading Rheostat

5KW , 230V

-

1

5

Tachometer

(0-1500)rpm

Digital

1

6

Connecting W ires

2.5sq.mm.

Copper

Few

PRECAUTIONS:



PROCEDURE:


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

maximum position of DC shunt generator field rheostat, DPST switch is

closed and starting resistance is gradually removed.


bringing the voltage to rated voltage by adjusting the field rheostat of

generator.

4. Load is varied gradually and for each load, voltmeter and ammeter readings

are noted.

33


TABULAR COLUMN:

S.No

V (Volts)

IL (Amps)

Eg (Volts)

MODEL GRAPH:

34


FORMULAE:

Eg = V + Ia Ra + Ia Rse (Volts)

Eg : Generated emf in Volts

V : Terminal Voltage in Volts

Ia : Armature Current in Amps

Ra : Armature Resistance in Ohms

Rse : Series field Resistance in Ohms

RESULT:

Thus load characteristics of DC series generator are obtained.

35


36


Ex. No: 5

AIM:

SPEED CONTROL OF DC SHUNT MOTOR

To obtain speed control of DC shunt motor by

a. Varying armature voltage with field current constant.

b. Varying field current with armature voltage constant

APPARATUS REQUIRED:


1 Ammeter (0-20) A MC 1

2 Voltmeter (0-300) V MC 1

3 Rheostats 500 0hm, 2A, 50 ohm ,3.5A Wire W ound E 2

4 Tachometer (0-3000) rpm Digital 1


PRECAUTIONS:

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

starting and stopping the motor.

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

of starting and stopping the motor.

PROCEDURE:


2. After checking the maximum position of armature rheostat and minimum position

of field rheostat, DPST switch is closed

(i) Armature Control:

1. Field current is fixed to various values and for each fixed value, by varying the

armature rheostat, speed is noted for various voltages across the armature.

(ii) Field Control:

1. Armature voltage is fixed to various values and for each fixed value, by adjusting

the field rheostat, speed is noted for various field currents.

2. Bringing field rheostat to minimum position and armature rheostat to maximum

position DPST switch is opened

37


Spee

d N

(rpm

)

Spee

d N

(rpm

)

TABULAR COLUMN:

(i) Armature Voltage Control:

S.No.

If1 = If2 = If3 = Armature

Voltage

Va ( Volts)

Speed

N

(rpm)

Armature

Voltage

Va ( Volts)

Speed

N

(rpm)

Armature

Voltage

Va ( Volts)

Speed

N

(rpm)

(ii) Field Control:

S.No.

Va1 = Va2 = Va3 = Field Current

If (A)

Speed

N (rpm) Field Current

If (A)

Speed

N (rpm) Field Current

If (A)

Speed

N (rpm)

MODEL GRAPHS:

If1 If2

If3

Va3

Va1

Va2

Va (Volts) If (Amps)

38


RESULT:

Thus the speed control of DC Shunt Motor is obtained using Armature and Field

control methods.

39


Effic

ienc

y %

Reg

ulat

ion

R %

LOAD TEST ON A SINGLE PHASE TRANSFORMER

MODEL GRAPHS:

R

Output Power (Watts)

40


Ex. No: 6 LOAD TEST ON A SINGLE PHASE TRANSFORMER

AIM:

To conduct load test on single phase transformer and to find efficiency and

percentage regulation.

APPARATUS REQUIRED:

S.No.

Apparatus

Range

Type

Quantity

1

Ammeter

(0-10)A

(0-5) A

MI

MI

1

1

2

Voltmeter

(0-150)V

(0-300) V

MI

MI

1

1

3

Wattmeter

(300V, 5A)

(150V, 5A)

UPF

UPF

1

1

4

Auto Transformer

1phase,(0-260)

V -

1

5

Resistive Load

5KW , 230V

-

1

6

Connecting W ires

2.5sq.mm

Copper

Few

PRECAUTIONS:

1. Auto Transformer should be in minimum position.

2. The AC supply is given and removed from the transformer under no load

condition.

PROCEDURE:


2. After checking the no load condition, minimum position of auto transformer and

DPST switch is closed.

3. Ammeter, Voltmeter and W attmeter readings on both primary side and secondary

side are noted.

4. The load is increased and for each load, Voltmeter, Ammeter and W attmeter

readings on both primary and secondary sides are noted.

5. Again no load condition is obtained and DPST switch is opened. 41

EE

63

65

- El

ec

tric

al

En

gin

ee

rin

g L

ab

or

ato

ry

42

S.No.

Load

Primary

Secondary

Input

Power

W1 x MF

Output

Power

W2 x MF

Efficiency

%

%

Regulation

V1

(Volts)

I1

(Amps)

W1

(Watts)

V2

(Volts)

I2

(Amps)

W2

(Watts)

FORMULAE:

Output Power = W 2 x Multiplication factor

Input Power = W 1 x Multiplication factor

E f f i c i e n c y % O u t p u t P o w e r I n p u t P o w e r

1 0 0 %

Regulation R % VNL VFL Secondary

VNL

100%

RESULT:

Thus the load test on single phase transformer is conducted.

43


OPEN CIRCUIT TEST

SHORT CIRCUIT TEST

44


Ex. No: 7

AIM:

OPEN CIRCUIT & SHORT CIRCUIT TEST ON A

SINGLE PHASE TRANSFORMER

To predetermine the efficiency and regulation of a transformer by conducting

open circuit test and short circuit test and to draw equivalent circuit.

APPARATUS REQUIRED:


1

Ammeter

(0-2)A

(0-5) A MI

MI 1

1

2 Voltmeter

(0-150)V,

(0-300)V

MI

1 Each

3

Wattmeter

(150V, 5A)

(300V, 5A) LPF

UPF 1

1

4 Connecting W ires 2.5sq.mm Copper Few

PRECAUTIONS:

1. Auto Transformer should be in minimum voltage position at the time of closing &

opening DPST Switch.

PROCEDURE:

OPEN CIRCUIT TEST:


2. After checking the minimum position of Autotransformer, DPST switch is closed.

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

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

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

opened.

45


TABULAR COLUMN:

OPEN CIRCUIT TEST:

Vo

(Volts) Io

(Amps) Wo

(Watts)

SHORT CIRCUIT TEST:

Vsc

(Volts) Isc

(Amps) Wsc

(Watts)

EQUIVALENT CIRCUIT:

ISCo

R

Ro1 Xo1

Vo

Ro Xo

L O A ZL = ZL/K2 D

N

46


c

2 1/2

o sc

SHORT CIRCUIT TEST:


2. After checking the minimum position of Autotransformer, DPST switch is closed.

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

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

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

opened.

FORMULAE:

Core loss: W o = VoIo cosφ o

W0

cos φ o V0 I o

I = Io cos φ o (Amps) I = Io sin φ o (Amps)

V0

Ro = ------- I

V0

Xo = ------- I

Wsc

Ro2 = ------- Is

2

Vsc

Zo2 = ------- Isc

Xo2 = ( Zo2 - Ro2 )

R02

Ro1 = ------- K2

X02

Xo1 = ------- K2

V2

K= ------- = 2 V1

Percentage Efficiency: for all loads and p.f.

E f f i c i e n c y η % = O u t p u t P o w e r x × K V A r a t i n g × 1 0 0 0 × c o sφ

= I n p u t P o w e r O u t p u t p o w e r + l o s s e s

x KVA rating 1000 cosφ =

( x KVA rating 1000 cosφ )+ W + x 2 W

47

Effic

ienc

y %


MODEL GRAPHS:

Output power (Watts)

% lagging

Power factor

% leading

48


Percentage Regulation:

x × I (R cos ± X sin ) x 100 R% = sc o2 o2

V2

+ = lagging - = leading

W here X is the load and it is 1 for full load, ½ for half load, ¾ load, ¼ load etc.. and the

power factor is, upf, o.8 p.f lag and 0.8 p.f lead

VIVA QUESTIONS:

1. W hy the S.C. test is performed on HV side?

2. W hy the O.C. test is performed on LV side?

3. W hat transformers are rated in kVA?

4. How the eddy current loss can be reduced?

RESULT:

Thus the efficiency and regulation of a transformer is predetermined by

conducting open circuit test and short circuit test and the equivalent circuit is drawn.

49


50


Ex. No: 8(a)

REGULATION OF ALTERNATOR BY EMF METHOD

AIM:

To predetermine the regulation of alternator by EMF method.

APPARATUS REQUIRED

Sl.No.

Name

Range

Type

Quantity

1

Voltmeter

(0-600V)

MI

1

2

Ammeter

(0-2)A

(0-10)A

MI

MI

1 each

3

Rheostat

300Ω/3A,

750Ω/2A

Wire wound

1 each

4

Connecting wires

As required

FORMULA open circuit voltage

Zs = at constant field current

short circuit current

Rac = 1.6 x Ra

XS = √ ZS2 – Rac2

ZS → Synchronous impedance (Ω)

XS → Synchronous Reactance (Ω)

Rac → Effective Resistance (Ω)

EO = √ (Vcosφ + IaRac)2 + (Vsinφ ± IaXS)2

(+ → lagging p.f and - →leading p.f)

V → rated voltage (volts)

Ia → rated armature current (volts)

Rac → effective resistance (Ω)

Cosφ→ power factor 51


52


E0 – V

% Regulation = ---------- x 100 %

V

PRECAUTIONS

TPST switch must be kept open.

Motor side rheostat must be kept in minimum position and alternator side

rheostat in maximum position.

PROCEDURE

OPEN CIRCUIT TEST

Make the connections as per the circuit diagram.

Switch on the supply.

Start the motor –alternator set by using starter.

Adjust the field rheostat of the motor to get the rated speed.

Increase the alternator field current in convenient steps and note down all the

meter readings upto 125% of the rated voltage.

Bring back the rheostat to the original position.

SHORT CIRCUIT TEST

Close the TPST switch and adjust the potential divider such that the maximum

full load current flows through the armature winding.

Note down all the meter readings.

Bring back the rheostats to original position and switch off the supply.

53


If2

(Amperes) Isc

(Amperes)

TABULATION

OPEN CIRCUIT TEST SHORT CIRCUIT TEST

Sl.No If

(Amperes) Open circuit voltage

E0 ( Volts)

Cosφ

% Regulation leading

Lagging

0

0.2

0.6

0.8

1

MODEL GRAPH

54


RESULT:

Thus the regulation of alternator was determine by using EMF method.

55


56


Ex. No:8(b)

REGULATION OF ALTERNATOR BY MMF METHOD

AIM To pre-determine the regulation of alternator by mmf method.

APPARATUS REQUIRED:

Sl.No. Name Range Type Quantity

1

2

3

4

5

Voltmeter

Ammeter Ammeter

Rheostat

Connecting wires

(0-600V)

(0-2A)

(0-10A)

300Ω/3A,

750Ω/2A

MI

MC,

MI

Wire wound

FORMULA

Ifr = √ If 2 + If 2 + 2 If1 If2 Cos (90±φ) 1 2

+ → lagging p.f and - →leading Pf

If1 → field current required to generate rated terminal voltage

If2 → field current required to circulate rated short circuit current

Ifr → resultant field current

E0 → The generated emf corresponding to Ifr (from graph)

E0 – V

% Regulation = ---------- x 100 %

V

PRECAUTIONS:

TPST switch must be kept open.

Motor side rheostat must be kept in minimum position and alternator side

rheostat in maximum position.

57


58


PROCEDURE

OPEN CIRCUIT TEST


Switch on the supply.

Start the motor –alternator set by using starter.

Adjust the field rheostat of the motor to get the rated speed.

Increase the alternator field current in convenient steps and note down all the

meter readings upto 125% of the rated voltage.

Bring back the rheostat to the original position.

SHORT CIRCUIT TEST

Close the TPST switch and adjust the potential divider such that the maximum full

load current flows through the armature winding.

Note down all the meter readings .

Bring back the rheostats to original position and switch off the supply.

59


If2

(Amperes) Isc

(Amperes)

TABULATION

OPEN CIRCUIT TEST SHORT CIRCUIT TEST

Sl.No If

(Amperes) Open circuit voltage

E0 ( Volts)

Cosφ

Lagging pf Leading pf

Ifr E0 %R Ifr E0 %R

0

0.2

0.6

0.8

1

MODEL GRAPH

%Regn

leading lagging

%Regn

60


RESULT Thus the regulation of alternator was determined using MMF method.

61


NAME PLATE DETAILS

3ǾSYNCHRONOUS MOTOR DC EXCITATION

62


Ex No:9

V AND INVERTED V CURVE OF THREE PHASE SYNCHRONOUS MOTOR

AIM

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

APPARATUS REQUIRED

S.No Name of the apparatus Type Range Quantity

1 Ammeter MI (0-5)A 2

2 Voltmeter MI (0-600)V 2

3 Ammeter MC (0-2)A 1

4 Rheostat 500Ω,2A 1

5 Wattmeter UPF 600V,5A 2

PRECAUTION

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

(2) The motor should be started without load.

(3) Initially TPST switch is in open position.

PROCEDURE

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

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

(3) Close the TPST switch.

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

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

motor.

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

synchronous motor, close the DPST switch.

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

current and the power factor for various values of excitation.

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

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

63


GRAPH:

64


RESULT:

The V-curves and inverted V-curves of the 3 phase synchronous motor

have been drawn.

65


66


Ex. No:10

LOAD TEST ON 3φ SQUIRREL CAGE INDUCTION MOTOR

AIM

To determine the performance characteristics of the given 3φ squirrel cage induction

motor by conducting load test.

APPARATUS REQUIRED

Sl.No. Apparatus Range Type Quantity

1 Voltmeter (0-600V) MI 1

2 Ammeter (0-10A) MI 1 3 Wattmeter UPF Dynamometer 2

4 Tachometer (0-600,10A) Analog 1 5 Connecting wires

FORMULA

Input power = W 1 x MF1 + W 2 x MF2 (watts)

Torque (T) = ( S1 ~ S2 ) x 9.81 x r (N-m)

Output power = 2ΠNT / 60 watts

Efficiency = output power / input power x 100%

S1, S2= spring balance readings in Kg.

R = radius of the brake drum in m (circumference / 2Π)

N = Actual speed of the rotor in rpm

T = Torque

NS = Synchronous speed rpm

67


68


PRECAUTIONS

There should be no load at the time of starting.

Auto transformer must be kept at minimum position

PROCEDURE


Switch on the supply and adjust the auto transformer to get the rated voltage and

note down the no load readings.

Adjust the loads and for various loads note down the corresponding meters

reading till the rated current is reached.

Unload the motor, bring back the auto transformer to minimum position and

switch off the supply.

RESULT

Thus the load test on three phase squirrel cage induction motor was performed

and performance characteristics were obtained.

69


70


Ex. No: 11

SPEED CONTROL OF THREE PHASE SLIP RING INDUCTION MOTOR

AIM:

To conduct the speed control test on three phase slip ring induction motor.

APPARATUS REQUIRED:

S.No Apparatus Range Type Quantity

1 Voltmeter (0-600) V MI 1

2 Ammeter (0-10)A MI 1

3 Connecting W ires As required

PROCEDURE


2. Note down the resistance in each phase using Multimeter.

3. Switch ON the A.C power supply.

4. Then the speed of the motor is taken for each resistance per phase.

5. The graph was drawn between resistance and speed

FORMULA

71


TABULAR COLUMN:

Sl.No Speed

(rpm) Resistance

(Ohms) Slip

MODEL GRAPH

speed

Resistance Vs Speed

Resistance

72


RESULT

Thus the speed control of three phase slip ring induction motor was performed

and the characteristics curves were drawn.

73


74


EX.NO:12

LOAD TEST ON SINGLE PHASE INDUCTION MOTOR

AIM To determine the performance characteristic of a given single phase capacitor

start induction motor by conducting load test.

APPARATUS REQUIRED:

S.No Apparatus Range Type Quantity

1 Voltmeter (0-300) V MI 1

2 Ammeter (0-10)A MI 1

3 Connecting W ires As required

4 Wattmeter 300V,10A upf 1

FUSE RATING

Fuse rating = 125% of rated current = 125/100 * 7.5

≈ 10A

FORMULA USED:

1) Torque ,T = (S1~S2)*9.81*R N.m

2) Output power = 2π NT/60*W

3) Effecting (η%) = 0/P Power/I/p Power*100

4) Slip (%S) = NS – N/NS*100

5) Power factor = Cos φ=W /VI

75


76


PRECAUTION

1) Before switching on the supply the variac is kept in minimum position.

2) Initially these should be on no load while starting the motor.

PROCEDURE

1) Connections are given as per the circuit diagram.

2) Switch on the supply at no load condition.

3) Apply the rotor voltage to the motor using the variac and note down the readings

at ammeter and wattmeter.

4) Vary the load in suitable steps and note down all the meter readings till fill load

condition.

GRAPH

1) Output Power Vs speed

2) Output power Vs Torque

3) Output power Vs Effecting

4) Output power Vs slip

5) Output power Vs Power factor

RESULT Thus the load test on the single phase induction motor has been conducted

and its performance characteristics determined.

77


78


Ex. No: 13

STUDY OF D.C & A.C MOTOR STARTERS

AIM:

To study the different kinds of D.C &A.C motor starters

APPARATUS REQUIRED:

Sl No. Name of the apparatus Quantity

1 Two Point starter 1

2 Three Point starter 1

3 Four Point starter 1

4 DOL Starter 1

5 Auto transformer Starter 1

6 Star-Delta Starter 1

7 Rotor Resistance Starter 1

THEORY :

The value of the armature current in a D.C shunt motor is given by Ia = ( V – Eb )/ Ra

Where V = applied voltage. Ra = armature resistance. E b = Back .e.m.f .

In practice the value of the armature resistance is of the order of 1 ohms and at the instant of starting the value of the back e.m.f is zero volts. Therefore under starting conditions the value of the armature current is very high. This high inrush current at the time of starting may damage the motor. To protect the motor from such dangerous current the D.C motors are always started using starters.

The types of D.C motor starters are

i) Two point starters

ii) Three point starters

iii) Four point starters.

79


80


The functions of the starters are

i) It protects the from dangerous high speed.

ii) It protects the motor from overloads.

i) TWO POINT STARTERS: ( refer fig 1)

It is used for starting D.C. series motors which has the problem of over speeding due to the loss of load from its shaft. Here for starting the motor the control arm is moved in clock-wise direction from its OFF position to the ON position against the spring tension. The control arm is held in the ON position by the electromagnet E. The exciting coil of the hold-on electromagnet E is connected in series with the armature circuit. If the motor loses its load, current decreases and hence the strength of the electromagnet also decreases. The control arm returns to the OFF position due to the spring tension,. Thus preventing the motor from over speeding. The starter also returns to the OFF position when the supply voltage decreases appreciably. L and F are the two points of the starter which are connected with the motor terminals.

ii) THREE POINT STARTER: ( refer fig 2 )

It is used for starting the shunt or compound motor. The coil of the hold on electromagnet E is connected in series with the shunt field coil. In the case of disconnection in the field circuit the control arm will return to its OFF position due to spring tension. This is necessary because the shunt motor will over speed if it loses excitation. The starter also returns to the OFF position in case of low voltage supply or complete failure of the supply. This protection is therefore is called No Volt Release (NVR).

Over load protection:

When the motor is over loaded it draws a heavy current. This heavy current also flows through the exciting coil of the over load electromagnet (OLR). The electromagnet then pulls an iron piece upwar6.ds which short circuits the coils of the NVR coil. The hold on magnet gets de-energized and therefore the starter arm returns to the OFF position, thus protecting the motor against overload. L, A and F are the three terminals of the three point starter.

iii) FOUR POINT STARTER:

The connection diagram of the four point starter is shown in fig 3. In a four point starter arm touches

the starting resistance, the current from the supply is divided into three paths. One through the starting resistance and the armature, one through the field circuit, and one through the NVR coil. A protective resistance is connected in series with the NVR coil. Since in a four point starter the NVR coil is independent of the of the field circuitt connection , the d.c motor may over speed if there is a break in the field circuit. A D.C motor can be stopped by opening the main switch. The steps of the starting resistance are so designed that the armature current will remain within the certain limits and will not change the torque developed by the motor to a great extent.

81


82


STUDY OF INDUCTION MOTOR STARTERS

AUTO –TRANSFORMER STARTING

An auto transformer starter consists of an auto transformer and a switch as shown in the fig. When the switch S is put on START position, a reduced voltage is applied across the motor terminals. When the motor picks up speed, say to 80 per cent of its rated speed, the switch is put to RUN position. Then the auto-transformer is cut out of the circuit and full rated voltage gets applied across the motor terminals.

The circuit diagram in the fig is for a manual auto-transformer starter. This can be made push button operated automatic controlled starter so that the contacts switch over from start to run position as the motor speed picks up to 80% of its speed. Over-load protection relay has not been shown in the figure. The switch S is air-break type for small motors and oil break type for large motors. Auto transformer may have more than one tapping to enable the user select any suitable starting voltage depending upon the conditions.

Series resistors or reactors can be used to cause voltage drop in them and thereby allow low voltage to be applied across the motor terminals at starting. These are cut out of the circuit as the motor picks up speed.

STAR- DELTA METHOD OF STARTING:

The startor phase windings are first connected in star and full voltage is connected across its

free terminals. As the motor picks up speed, the windings are disconnected through a switch and they are reconnected in delta across the supply terminals. The current drawn by the motor from the lines is reduced to as compared to the current it would have drawn if connected in delta.The motor windings, first in star and then in delta the line current drawn by the motor at starting is reduced to one third as compared to starting current with the windings delta-connected.

In making connections for star-delta starting, care should be taken such that sequence of supply

connections to the winding terminals does not change while changing from star connection to delta connection. Otherwise the motor will start rotating in the opposite direction, when connections are changed from star to delta. Star-delta starters are available for manual operation using push button control. An automatic star – delta starter used time delay relays(T.D.R) through which star to delta connections take place automatically with some pre-fixed time delay. The delay time of the T.D.R is fixed keeping in view the starting time of the motor.

83


FULL VOLTAGE OR DIRECT –ON-LINE STARTING

When full voltage is connected across the stator terminals of an induction motor, large current is drawn by the windings. This is because, at starting the induction motor behaves as a short circuited transformer with its secondary, i.e. the rotor separated from the primary, i.e. the stator by a small air- gap.

At starting when the rotor is at standstill, emf is induced in the rotor circuit exactly similar to the

emf induced in the secondary winding of a transformer. This induced emf of the rotor will circulate a very large current through its windings. The primary will draw very large current from the supply mains to balance the rotor ampere-turns. To limit the stator and rotor currents at starting to a safe value, it may be necessary to reduce the stator supply voltage to a low value. If induction motors are started direct-on-line such a heavy starting current of short duration may not cause harm to the motor since the construction of induction motors are rugged. Other motors and equipment connected to the supply lines will receive reduced voltage. In industrial installations, however, if a number of large motors are started by this method, the voltage drop will be very high and may be really objectionable for the other types of loads connected to the system. The amount of voltage drop will not only be dependent on the size of the motor but also on factors like the capacity of the power supply system, the size and length of the line leading to the motors etc. Indian Electricity Rule restricts direct on line starting of 3 phase induction motors above 5 hp.

RESULT:

Thus the construction and working of different starters for starting D.C series, shunt, compound and three phase induction motors are studied.


MODEL GRAPHS:

86


Ex No : 14

AIM:

LOAD TEST ON DC COMPOUND MOTOR

To conduct load test on DC compound motor and to find its efficiency.

APPARATUS REQUIRED:


1 Ammeter (0-20)A MC 1


3 Rheostat 500, 2A Wire Wound 1

4 Tachometer (0-1500) rpm Digital 1

5 Connecting Wires 2.5sq.mm. Copper Few

PRECAUTIONS:

1. DC compound motor should be started and stopped under no load condition.

2. Field rheostat should be kept in the minimum position.


PROCEDURE:


2. After checking the no load condition, and minimum field rheostat position, DPST

switch is closed and starter resistance is gradually removed.

3. The motor is brought to its rated speed by adjusting the field rheostat.

4. Ammeter, Voltmeter readings, speed and spring balance readings are noted under

no load condition.

5. The load is then added to the motor gradually and for each load, voltmeter, ammeter,

spring balance readings and speed of the motor are noted.

6. The motor is then brought to no load condition and field rheostat to minimum

position, then DPST switch is opened.

87


TABULAR COLUMN:

S.No.

Voltage

V

(Volts)

Current

I

(Amps)

Spring

Balance

Reading

(S1 S2)

Kg

Speed

N

(rpm)

Torque

T

(Nm)

Output

Power

Pm

(Watts)

Input

Power

Pi

(Watts)

Efficiency

%

S1(Kg) S2(Kg)



RESULT:

Thus load test on DC compound motor is conducted and its efficiency is determined.

89


Model Graph

90


EXP.NO: 15 SWINBURNE’STEST DATE:

AIM:

To predetermine the efficiency o the D.C. machine when it act as

(i) Motor

(ii) Generator

APPARATUS REQUIRED:-

Sl.No. Name of the apparatus Range Type Quantity

1. Ammeter (0 -5) A MC 1

2. Ammeter (0 - 2) A MC 1

3. Voltmeter (0 - 300)V MC 1

4. Rheostat 500 ohm, 2 A Wire wound 1

5. Tachometer Digital 1

PRECAUTION:

1. The field rheostat should be kept at minimum resistance position.

2. There should be no load at the time of starting the

experiment.

PROCEDURE:

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

2. The DPST switch is closed.

3. The motor is started with the help of three point starter.

4. The field rheostat of the motor is adjusted to bring the motor speed to the

rated value.

5. The no load current, voltage and shunt field current are

noted.


Line

Current,

IL

(A)

Field

current

If

(A)

Ia =

IL -If (A)

2

Ra

Constant

Loss

Total

Loss

(watts)

Input

Power

(watts)

Output

Power

(watts)

Efficiency

%

TABULAR COLOUMN

S.N o

Voltage, V (volts)

Field current, If

(A) No load current, I0

(A)

For generator

Line

Current,

IL

(A)

Field

current

If

(A)

Ia =

IL

+If

(A)

Wcu=I 2

a

Ra

Constant

Loss

Total

Loss

(watts)

Input

Power

(watts)

Output

Power

(watts)

Efficiency

%

For motor

Wcu=Ia

Measurement of Ra:

Voltage (v) Current(A) Armature resistance

Ra(ohms)

92


FORMULA USED:

Constant loss Wc = VIa – (IO –If)2 Ra

Ra – Resistance of armature For Motor

Armature Current Ia = IL - If

Armature copper loss Wcu = 2Ia Ra

Total loss Wt = Wc + Wcu

Input power Pi = VIL

Output Power Po = Pi - Wt

Efficiency =

For Generator

Armature Current Ia = IL + If

Armature copper loss Wcu = 2Ia Ra

Total loss Wt = Wc + Wcu

Output power Po = VIL

Input Power Pi = Po + Wt

Efficiency =

RESULT:

Thus the efficiency of the DC machine has been predetermined and

characteristics were drawn.

93

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