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LABORATORY PRACTICE

SAFETY RULES

1. SAFETY is of paramount importance in the Electrical Engineering Laboratories.

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

attention in handling electrical equipment and follow safety practices in the

laboratory. (Electricity is a good servant but a bad master).

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

such contact may subject you to electrical shock)

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

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

will be protected from electrical shock)

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

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

happens to be a rotating machine)

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

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

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

may touch a live point and thereby subject you to electrical shock)

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

parts of the body reduce the contact resistance thereby increasing the severity of the

shock)

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

you will be touching the live parts in the circuit)

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

strictly as per the approved circuit diagram.

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

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

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

such defective leads.

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

Safety devices protect YOU and your equipment.

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

and approved by the staff member.

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

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

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

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

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

the staff member.

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

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

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

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

drums:

i. Avoid the brake-drum from getting too hot by putting just enough water into

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

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

the braking belts)

ii. Do not stand in front of the brake-drum when the supply to the load-test

circuit is switched off. (Otherwise, the hot water in the brake-drum will splash

out on you)

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

the plastic bottle with nozzle and then dry off the drum with a sponge which

is available in the laboratory.(The water, if allowed to remain in the brake-

drum, will corrode it)

21. Determine the correct rating of the fuses to be connected in the circuit after

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

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

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

instruments like ammeters and watt-meters in case of over load, an under-rated fuse

may not allow one even to start the experiment)

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

overshoots, as the starting current is around 5 times the full load rating of the motor.

Moving coil ammeters being very delicate may get damaged due to high starting

current. A switch has been provided on such meters to disconnect the moving coil of

the meter during starting. This switch should be closed after the motor attains full

speed. Moving iron ammeters and current coils of wattmeter’s are not so delicate and

hence these can stand short time overload due to high starting current. No such switch

is therefore provided on these meters. Moving iron meters are cheaper and more

rugged compared to moving coil meters. Moving iron meters can be used for both a.c.

and d.c. measurement. Moving coil instruments are however more sensitive and more

accurate as compared to their moving iron counterparts and these can be used for d.c.

measurements only. Good features of moving coil instruments are not of much

consequence for you as other sources of errors in the experiments are many times

more than those caused by these meters.

PRE LAB QUESTIONS:

Experiment No.

LOAD TEST ON SINGLE PHASE INDUCTION MOTOR

AIM:

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

performance characteristics.

APPARATUS REQUIRED:

S.NO APPARATUS SPECIFICATIONS QUANTITY

1

2

3

4

VOLTMETER

AMMETER

WATTMETER

TACHOMETER

(0-300V) MI

(0-10A) MI

(300V,10A,UPF)

(0-10000 RPM)

1

1

1

1

FORMULAE:

1. Circumference of the brake drum = 2ΠR (m)

R = Radius of the brake drum

2. Input power =W (watts)

W = wattmeter readings

3. Torque (T) = 9.81* R * (S1 ~ S2) (N-m)

S1, S2 = spring balance readings (Kg)

4. Output power = 60

2 NT(watts)

N- Speed in rpm

5. % Efficiency (η) = 100xpowerinput

poweroutput

6. Power factor, cos Φ= VI

W

7. % Slip, s = 100

Ns

NNs

NS = synchronous speed = P

f120(rpm)

P = no. of poles

f=frequency of supply (Hz)

PRECAUTIONS:

1. The auto transformer is kept at minimum voltage position.

2. The motor is started at no load condition.

PROCEDURE:

1. Connections are given as per the circuit diagram

2. The DPST switch is closed and the single phase supply is given

3. By adjusting the variac the rated voltage is applied and the corresponding no load

values of speed, spring balance and meter readings are noted down. If the wattmeter

readings show negative deflection on no load, switch of the supply & interchange the

terminals of current coils (M & L) of the wattmeter. Now, again starting the motor

(follow above procedure for starting), take readings.

4. The procedure is repeated till rated current of the motor.

5. The motor is unloaded, the auto transformer is brought to the minimum voltage

position, and the DPST switch is opened.

6. The radius of the brake drum is measured.

TABULAR COLUMN:

V

volts

I

Amps

Speed

N

(rpm)

Wattmeter

reading

(watts)

Spring balance

readings (Kg)

Torque

(T)

N-m

Output

Power

(watts)

Power

factor

cos Φ

% efficiency

(η)

%Slip(s)

S1 S2 S1~S2

OBS ACT

MODEL GRAPH:

D

P

S

T

S

W

I

T

C

H

230V,

1 AC

Supply

Link

Fuse P

N

15A

Auto

Tra

nsf

orm

er

230/(

0-2

70)

V

M1

M2

(0-10)A

MI

(0-300)V

MI

300V, 10A, UPF

Brake Drum

S1 S2

Kg Kg

Rotor

S1 S2

FUSE RATING:

125% of rated current

125 x 9.5

---------------- = 15 A

100

NAME PLATE DETAILS:

Rated Voltage : 220V

Rated Current : 9.5A

Rated Power : 3HP

Rated Speed : 1470 RPM

C

S1, S2- AUXILLARY WINDING

M1, M2- MAIN WINDING

CIRCUIT DIAGRAM: LOAD TEST ON SINGLE PHASE INDUCTION MOTOR

A M L

C V

V

RESULT:

POST LAB QUESTIONS:

PRELAB QUESTIONS:

Experiment No.

LOAD TEST ON THREE PHASE SQUIRREL CAGE INDUCTION

MOTOR AIM:

To conduct load test on given 3-phase squirrel cage induction motor and to plot its

performance characteristics.

APPARATUS REQUIRED:

SI.NO APPARATUS SPECIFICATIONS QUANTITY

1

2

3

4

VOLTMETER

AMMETER

WATTMETER

TACHOMETER

(0-600V) MI

(0-5A) MI

(600V,10A,UPF)

(0-10000 RPM)

1

1

2

1

FORMULAE:

1. circumference of the brake drum = 2ΠR (m)

R = Radius of the brake drum

2. Input power W=W1+W2 (watts)

W1, W2 = wattmeter readings

3. Torque (T) = 9.81* R * (S1 ~ S2) (N-m)

S1, S2 = spring balance readings (Kg)

4. Output power = 60

2 NT(watts)

5. % Efficiency (η) = 100xpowerinput

poweroutput

6. Power factor, Cos Φ = VI

WW

3

21

Cos Φ= Power factor

7. %Slip, s = 100

Ns

NNs

NS = synchronous speed = P

f120 (rpm)

P = no. of poles

f=frequency of supply (Hz)

PRECAUTIONS:

1. The motor is started at no load condition.

PROCEDURE:


2. The TPST switch is closed and the 3-phase supply is given

3. The motor is started with a DOL starter.

4. No load readings are noted down.

5. If any one of the wattmeter shows negative deflection, the connections of M and L in

the wattmeter are interchanged after switching off the supply.

6. Gradually the motor is loaded and in each case all the meter readings are noted down

and the procedure is repeated till the rated current is obtained.

7. The motor is unloaded, the auto transformer is brought to the minimum voltage

position, and the TPST Switch is opened.

8. The radius of the brake drum is measured.

TABULAR COLUMN:

V

volts

I

Amps

Speed

N

(rpm)

Wattmeter reading

(Watts)

Spring balance

readings (Kg)

Torque

(T)

N-m

Output

power

(Watts)

Power

factor

(cos Φ)

%

efficien

cy

(η)

% Slip

(s) W1 W2

W1+W2

S1 S2 S1~S2

Obs Act Obs Act

MODEL GRAPH:

CIRCUIT DIAGRAM: LOAD TEST ON A THREE PHASE SQUIRREL CAGE INDUCTION MOTOR

RESULT:

POST LAB QUESTIONS

Experiment No.

NO LOAD AND BLOCKED ROTOR TEST OF THREE PHASE

SLIPRING INDUCTION MOTOR – CIRCLE DIAGRAM AND

EQUIVALENT CIRCUIT

AIM:

To predetermine the performance characteristics of 3-Ø slip ring induction motor

from circle diagram by conducting no load and blocked rotor test and to draw the equivalent

circuit.

APPARATUS REQUIRED:


1

2

3

VOLTMETER

AMMETER

WATTMETER

(0-600V) MI, (0-300V)MI

(0-10A) MI, (0-5ª)MI

(300V,10A,UPF)

(600V,5A,LPF)

2

2

2

2

FORMULAE:

NO LOAD TEST:

Cos Φ0 = 00

0

3 IV

W

Where W0 = no-load input power in watts (watts)

V0 = line voltage on no-load

I0 = line current on no-load

Iw= Io Cos Φ0 Amps

Ro= w

ph

I

V )(0=

wI

V

3

0 Ω

Iµ= Io Sin Φ0 Amps

Xo= I

V ph)(0=

I

V

3

0 Ω

BLOCKED ROTOR TEST:

ISN = SC

SCV

VI

WSN=

2

SC

SN

scI

IW (watts)

Cos Φsc = IscVsc

WSC

3

X01= )(2

01

2

01 RZ

R2’ = R01/ 2 Ω

RL’ = R2

’

s

s1 Ω

Where

V0= No load voltage in volts

I0= No load current in amps

W0= No load power in watts

Iw= Working current in amps

Iµ= Magnetizing current in amps

X0= No load reactance in Ω

VSC= Short circuit voltage volts

ISC= Short circuit current in amps

WSC= Short circuit power in watts

s= 5% (Assumed)

PROCEDURE:

NO LOAD TEST:


2. Initially the motor is kept at no load condition.

3. The TPST switch is closed

4. By adjusting the 3Φ auto transformer the machine is brought to rated voltage.

5. The ammeter, voltmeter and wattmeter readings are noted down.

BLOCKED ROTOR TEST:


2. Load is applied to prevent the rotor from rotating.

3. Close the TPST switch.

4. By adjusting the 3Φ auto transformer rated current is allowed to circulate.

5. The ammeter, voltmeter and wattmeter readings are noted down.

TABULATION

NO LOAD TEST

V0

(volts)

I0

(amps)

W1

(watts)

W2

(watts)

W0

(watts)

BLOCKED ROTOR TEST

VSC

(volts)

ISC

(amps)

W1

(watts)

W2

(watts)

WSC

(watts)

MODEL EQUIVALENT CIRCUIT:

MODEL GRAPH:

NAME PLATE DETAILS:

Stator rotor Rated Voltage : 415V 185V

Rated Current : 4.5A 7.5A

Rated Power : 3HP


CIRCUIT DIAGRAM: CIRCLE DIAGRAM ON 3 PHASE SLIP RING INDUCTION MOTOR

NO-LOAD TEST:

FUSE CALCULATION:

0.25*4.5= 5A

NAME PLATE DETAILS:

Stator rotor Rated Voltage : 415V 185V

Rated Current : 4.5A 7.5A

Rated Power : 3HP


BLOCKED ROTOR TEST:

FUSE CALCULATION:

1.25*4.5= 10A

RESULT:

CONSTRUCTION OF CIRCLE DIAGRAM

By using the data obtained from the no load test and the blocked rotor test, the circle

diagram can be drawn using the following steps:

1. Take reference phasor V as vertical (Y-axis)

2. Select suitable current scale such that diameter of circle is 20-30cm.

3. From No laod test, I0 and 0 are obtained. Draw vector I0, lagging V by angle 0.

This is line OA

4. Draw horizontal line through extremity of I0 i.e., A parallel to horizontal axis.

5. Draw the current ISN calculated from ISC with the same scale, lagging V by angle

SC, from origion O. This is phasor OB.

6. Join AB. The line AB is called output line.

7. Draw a perpendicular bisector to AB Extend it to meet line AD at point C. This

is the centre of the circle.

8. Draw the circle with C as a centre and radius equal to AC. This meets the

horizontal line drawn from A at B.

9. Draw the perpendicular from point B on the horizontal axis to meet AF line at D

and meet horizontal axis at E.

10. Torque line:

The torque line separates stator and rotor copper losses.

The vertical distance BD represents power input at short circuit i.e., WSN which

consist of core loss, stator and rotor copper losses.

FD = DE = fixed loss

AF sum of stator & rotor copper losses.

Pt ‘G’ is located as

losscopperStator

losscopperRotor

GD

BG

The line AG in called torque line

Power Scale: As AD represents WSN i.e., power input on short circuit at normal voltage, the

power scale can be obtained as

Power scale = cmWBE

WSN /)(

(BE) = Distance BE in cm

Location of point E (slip ring induction motor):

K = 2

1

I

I= transformation ratio

2

1

2

1

2

1

2

1

2

2

2

I

I

R

R

RI

RI

losscopperstator

losscopperRotor

EF

AE

2

21

2K

RR = Rotor resistance referred to stator.

1

1

2

R

R

GD

BG

Thus pt G can be obtained by dividing the line BD in the ratio 1

'

2 RR

Location of point D (squirrel cage induction motor):

In a squirrel cage motor, the stator resistance can be measured by conducting resistance test.

i.e., Stator copper loss = 1

23 RI SN where SNI is phase value.

Neglecting core loss, WSN = stator Cu loss + Rotor Cu loss

i.e., Rotor copper loss = 1

23 RIW SNSN

1

2

1

2

3

3

RI

RWSN

GD

BG

SN

SN

Dividing line BD in this ratio, the point G can be obtained and hence AG represents torque

line.

To get the torque line, join the points A and G.

11. To find the full load quantities, draw line BK (=Full load output/power scale).

Now, draw line PK parallel to output line meeting the circle at point P.

12. Draw line PT parallel to Y-axis meeting output line at Q, torque line at R, constant

loss line at S and X-axis at T.

POSTLAB QUESTIONS:

PRELAB QUESTIONS:

Experiment No.

DETERMINATION OF DIRECT AXIS (Xd) AND QUADRATURE AXIS

(Xq) REACTANCES

AIM:

To find the direct axis reactance Xd and quadrature axis reactance Xq by conducting

slip test.

APPARATUS REQUIRED:


1

2

3

4

VOLTMETER

AMMETER

RHEOSTAT

TACHOMETER

(0-300V) MI

(0-5A) MI

300Ω,1.2A

(0-10000 RPM)

2

1

1

1

FORMULAE:

Xd = Maximum armature voltage/phase

Minimum armature current/phase

Xq = Minimum armature voltage/phase

Maximum armature current/phase

PRECAUTION:

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

PROCEDURE:


2. The DPST switch is closed

3. The rheostat is varied from the minimum resistance position so as to bring the speed

to a value below or near to rated speed of the alternator

4. The TPST switch is closed keeping the variac in the minimum position.

5. The variac is varied to apply 15-20% of the rated voltage of alternator is observed.

6. Check the voltage in the field coil, if it reads high the phase sequence is changed so

that the voltmeter reads zero.

7. The maximum and minimum deflections of voltmeter and ammeter are noted.

8. The variac is brought to minimum position and TPST Switch is opened. The field

rheostat is brought to minimum position and DPST Switch is opened

TABULAR COLUMN:

VMAX VMIN IMAX IMIN

CIRCUIT DIAGRAM: DETERMINATION OF DIRECT AXIS (Xd) AND QUADRATURE AXIS (Xq) REACTANCES

RESULT:

POSTLAB QUESTIONS:

PRELAB QUESTIONS

Experiment No.

PREDETERMINATION OF REGULATION BY EMF AND MMF

METHOD

AIM:

To predetermine the regulation of alternator by emf and mmf methods

APPARATUS REQUIRED:


1

2

3

4

VOLTMETER

AMMETER

RHEOSTAT

TACHOMETER

(0-600V) MI

(0-5A) MI

300Ω,1.2A

(0-10000 RPM)

2

1

1

1

FORMULAE:

EMF METHOD:

Synchronous impedance, Zs = phaseSCcurrent

phasevoltageOC

/

/(at constant If)

Synchronous reactance, Xs = )(22 RacZs

Where Rac = armature resistance

For rated conditions,

EMF, E0 = 22 )sin()cos( IXsVphIRaVph

+ corresponds to lagging power factor

- corresponds to leading power factor

% Regulation = 1000

xVph

VphE

MMF METHOD:

If1 = field current corresponding to Isc

E = Vph + IRa cosΦ

If2 = field current corresponding to E from graph

If0 = ))90(180cos(21221( 22 IfIfIfIf

E0 = open circuit voltage corresponding to If0 (from graph)

% Regulation = 1000

xVph

VphE

PRECAUTION:

1. The Motor field rheostat is kept at minimum resistance position.

2. The Generator field rheostat should be kept at maximum resistance position.

PROCEDURE:

OC TEST:


2. The TPST switch of the alternator is kept opened.

3. The DPST-1 switch is closed

4. The motor field rheostat is varied such that the alternator runs at rated speed.

5. The DPST-2 switch is closed.

6. The Generator field rheostat is varied in step and the readings of If and V are

noted, till 125% of the rated voltage is obtained.

SC TEST:


2. The DPST-1 switch is closed

3. The motor field rheostat is varied such that the alternator runs at rated speed.

4. The TPST switch is closed.

5. The DPST-2 switch is closed.

6. The Generator field rheostat is varied to bring rated current of alternator and the

corresponding If is noted.

OC TEST:

FIELD

CURRENT(If)

(amps)

LINE

VOLTAGE(VL)

(volts)

PHASE

VOLTAGE

(Vph)(volts)

SC TEST:

FIELD

CURRENT(If)(

amps)

S.C.CURRENT

(ISC)(amps)

EMF METHOD:

cos Ø E0(volts) % regulation

LAG LEAD LAG LEAD

Unity

MMF METHOD:


LAG LEAD LAG LEAD

Unity

MODEL GRAPH:

10A

CIRCUIT DIAGRAM: REGULATION OF THREE PHASE ALTERNATOR BY EMF AND MMF METHODS

RESULT:

POSTLAB QUESTIONS

PRELAB QUESTIONS

Experiment No.

PREDETERMINATION OF REGULATION BY ZPF METHOD

AIM:

To predetermine the regulation of alternator by at full load different power factor by

ZPF method.

APPARATUS REQUIRED:


1

2

3

4

5

VOLTMETER

AMMETERS

RHEOSTAT

TACHOMETER

REACTIVE LOAD

(0-600V) MI

(0-5A) MI

(0-10A)MI

300Ω,1.2A

(0-10000 RPM)

(1-15) amps

1

1

1

2

1

1

FORMULAE:

EMF, E1 = 22 )sin()cos( LIXVphIRaVph

+ corresponds to lagging power factor

- corresponds to leading power factor

IXL = RS (from graph)

If2 = PS (from graph)

If1 = field current corresponding to E1 (from graph)

If0 = ))90(180cos(21221( 22 IfIfIfIf

E0 = open circuit voltage corresponding to If0 (from graph)

% Regulation = 1000

xVph

VphE

PRECAUTION:

1. The motor field rheostat is kept at minimum resistance position.

2. The potentiometer should be kept at minimum voltage position.

PROCEDURE: 1. Connections are given as per the circuit diagram

2. The no load test and the short circuit test is performed and the readings are tabulated.

(refer emf and mmf procedure).

3. Before ZPF test the motor has to be brought to rated speed under no load condition.

4. The field current of the alternator is adjusted using field rheostat so that the voltage

across the alternator reads 380V and then the inductive load is connected by closing

the TPST switch, the load is adjusted so that the alternator reads the rated value of

current.

5. The readings taken are tabulated.

6. Then the triangle is projected with the same dimension and ZPF curve is drawn for

the field current corresponding to rated short circuit current. The altitude RS gives

IXL drop and PS gives If2 (field current necessary to overcome demagnetizing effect

of armature reaction at full load). From the above values the regulation at different

power factors are found.

OC TEST:

FIELD

CURRENT(If)

(amps)

LINE

VOLTAGE(VL)

(volts)

PHASE

VOLTAGE

(Vph)(volts)

SC TEST:

FIELD

CURRENT(If)

(amps)

S.C.CURRENT

ISC(amps)

ZPF TEST:

If(amps) VZPF(VOLTS) ISC(amps)

ZPFMETHOD:


LAG LEAD LAG LEAD

Unity

MODEL GRAPH:

PROCEDURE TO DRAW THE POTIER TRIANGLE (ZPF METHOD):

(All the quantities are in per phase value)

1. Draw the Open Circuit Characteristics (Generated Voltage per phase VS Field

Current)

2. Mark the point A at X-axis, which is obtained from short circuit test with full load

armature current.

3. From the ZPF test, mark the point P for the field current to the corresponding rated

armature current and the rated voltage.

4. Draw the ZPF curve which passing through the point A and P in such a way parallel

to the open circuit characteristics curve.

5. Draw the tangent for the OCC curve from the origin (i.e.) air gap line.

6. Draw the line PX from P towards Y-axis, which is parallel and equal to OA.

7. Draw the parallel line for the tangent from R to the OCC curve.

8. Join the points R and S also drop the perpendicular line PX, where the line RS

represents armature leakage reactance drop (IXL)

PS represents armature reaction excitation (Ifa).

CIRCUIT DIAGRAM: PREDETERMINATION OF REGULATION BY ZPF METHOD

FUSE CALCULATION: MOTOR ALTERNATOR

1.25*10=15A 1.25*4.2=5A

RESULT:

POST LAB QUESTIONS

PRELAB QUESTIONS

Experiment No.

DETERMINATION OF V AND INVERTED V CURVES OF

SYNCHRONOUS MOTOR

AIM:

To determine the V and inverted V curve of synchronous motor

APPARATUS REQUIRED:


1

2

3

4

VOLTMETER

AMMETERS

RHEOSTAT

WATTMETER

(0-600V) MI

(0-2A) MC

(0-10A)MI

300Ω,1.2A

600V,10A,UPF

1

1

1

1

2

FORMULAE:

Φ =

21

211 3tancosWW

WW

Where W1 = wattmeter reading 1

W2 = wattmeter reading 1

PRECAUTION:

1. The VARIAC is kept at minimum position.

2. The potentiometer should be kept at minimum voltage position.

PROCEDURE: 1. Connections are as per the circuit diagram

2. The TPST switch is closed.

3. By varying auto synchronous motor starter the voltage is adjusted to 30-40% of rated

voltage.

4. Close the DPST switch.

5. Adjusted the rheostat and bring for rated current.

6. Now the Voltmeter is adjusted for rated voltage values.

7. The values of If1, W1 and W2 are noted down.

8. By adjusting the rheostat below rated current the corresponding reading are noted

down.

9. At some point the value of Ia will increase and the above procedure is repeated till the

rated value of current.

10. If any wattmeter shows negative deflection, change the current coil terminals of

wattmeter.

TABULAR COLUMN:

Ia If V W1(watts) W2(watts) W1+W2(watts) COSΦ

Amps Amps Volts OBS ACT OBS ACT

MODEL GRAPH:

CIRCUIT DIAGRAM: V AND INVERTED V CURVES OF SYNCHRONOUS MOTOR

RESULT:

POSTLAB QUESTIONS

.

PRELAB QUESTIONS

Experiment No.

SYNCHRONISATION OF ALTERNATOR TO INFINITE BUSBAR

AIM:

To synchronize the 3Φ alternator to the infinite bus bar.

APPARATUS REQUIRED:


1

2

3

VOLTMETER

AMMETERS

RHEOSTAT

SYNCHRONISING LAMPS

(0-600V) MI

(0-2A) MC

300Ω,1.2A

350Ω,2A

230V,15A

2

1

1

1

6

PROCEDURE:

1) The DPST-1 is closed and the motor field rheostat is adjusted to make the

alternator run at rated speed.

2) The DPST-2 is closed and by keeping the TPST open, adjusts the alternator field

rheostat to supply the voltage equal to infinite bus bar.

3) The phase sequence of the alternator is made as same as that of the infinite bus bar

by observing the sequence of glowing of synchronizing lamps. If the phase

sequence is not same, any of the two phases are interchanged.

4) The field rheostat is adjusted to bring the frequency of the alternator to same

frequency of infinite bus bar. When the phase sequence of the two sides are same

all the lamps will begin to glow bright and dark simultaneously. In this condition,

when the frequencies are equal, the variation of lamps bright to dark is lowest.

5) At the dimmest point the TPST switch is closed thereby synchronizing the

alternator to the bus bar.

CIRCUIT DIAGRAM: SYNCHRONISATION OF ALTERNATOR TO INFINITE BUSBAR

RESULT:

POSTLAB QUESTIONS

.

PRELAB QUESTIONS (10):

Experiment No.

ROTOR RHEOSTAT SPEED CONTROL OF SLIP RING INDUCTION

MOTOR

AIM:

To vary the speed of the slip ring induction motor using rotor rheostat control.

APPARATUS REQUIRED:


1

2

3

Voltmeter

Ammeter

Tachometer

(0-600V) MI

(0-10A) MI

0-10000 (rpm)

1

1

1

PROCEDURE:

1. The Connection are made as per circuit diagram

2. The TPST switch is closed and three phase supply is given.

3. The motor is started with rotor rheostat starter.

4. The rotor resistance is varied and corresponding values of speed, voltage and

current are noted down.

TABULAR COLUMN

Voltage

(V)

Current (A) Resistance () Speed (rpm)

MODEL GRAPH:

Speed vs resistance

1390

14301440

14501460

1470

13401360138014001420144014601480

Resi

stan

ce (W

)46

.632

.221

.8

12.12

5.88

resistance(ohm)

sp

eed

(rp

m)

Speed (rpm)

CIRCUIT DIAGRAM: ROTOR RHEOSTAT SPEED CONTROL OF INDUCTION MOTOR

RESULT:

.

POSTLAB QUESTIONS

PRELAB QUESTIONS

Experiment No.

SPEED CONTROL OF INDUCTION MOTOR BY VARIABLE

FREQUENCY METHOD

AIM: To control the speed of the 3 phase induction motor by changing the supply frequency

and to plot the speed Vs frequency curve.

APPARATUS:


1

2

3

4

5

Voltmeter

Ammeter

Tachometer

Frequency meter Digital

. Rheostat Wire Wound

(0-600V) MI

(0-10A) MI

(0-2)A MC

0-10000 (rpm)

(0-60Hz)

300Ω, 1.2A

2

1

1

1

1

2

PRECAUTIONS:

i) TPST in open position

ii) DPST1 and DPST2 in open position

iii) Motor field rheostat in minimum position

iv) Potential divider in minimum voltage position

v) Autotransformer at minimum voltage position

PROCEDURE:

1. Make the connections as shown in diagram.

2. Switch on the DC supply to the DC motor by closing the switch DPST1. Start the DC

shunt motor using 3-point starter. Adjust the field rheostat of the alternator and bring

it to rated speed.(1500rpm).

3. Now, dc supply is given to the alternator field winding and adjust the potential divider

so that the generated voltage is rated value (410V).

4. Close the TPST switch. Increase the autotransformer. Induction motor starts running

on no load. Apply rated voltage by adjusting autotransformer. Note down the

frequency, voltage and speed of the induction motor. Now, decrease the frequency.

Decrease the voltage and frequency in proportion and note down the frequency,

voltage and speed of the induction motor each time. This procedure is continued till

frequency decreases to 48Hz.Switch off the supply after bringing the motor to no-

load.

TABULATION

Induction motor on no load

Line voltage

In volts

Frequency

In Hz

Speed of IM

In rpm

MODEL GRAPH:

NAME PLATE DETAILS:

Motor Alternator

Rated Voltage : 220V 415V

Rated Current : 19A 4.2A

Rated Power : 3HP 5KVA

Rated Speed : 1500 RPM 1500 RPM

CIRCUIT DIAGRAM: SPEED CONTROL OF INDUCTION MOTOR BY VARIABLE FREQUENCY METHOD

Fuse calculation:

125% of Rated current=1.25*19=30A

RESULT:

POSTLAB QUESTIONS:

1.

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