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 brakedrums:
i.
ii.
iii.
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)
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)
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 brakedrum, 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
1
2
3
4
APPARATUS
VOLTMETER
AMMETER
WATTMETER
TACHOMETER
SPECIFICATIONS
(0-300V) MI
(0-10A) MI
(300V,10A,UPF)
(0-10000 RPM)
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)
2NT
(watts)
60
N- Speed in rpm
4. Output power =
output power
x100
input power
W
6. Power factor, cos Φ=
VI
Ns  N
 100
7. % Slip, s =
Ns
120 f
NS = synchronous speed =
(rpm)
P
P = no. of poles
f=frequency of supply (Hz)
5. % Efficiency (η) =
QUANTITY
1
1
1
1
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
Speed
Amps
N
(rpm)
Wattmeter
reading
(watts)
Spring
balance
readings (Kg)
S1
S2 S1~S2
Torque
(T)
N-m
OBS
ACT
Output
Power
(watts)
Power
factor
cos Φ
% efficiency
(η)
%Slip(s)
MODEL GRAPH:
CIRCUIT DIAGRAM: LOAD TEST ON SINGLE PHASE INDUCTION MOTOR
300V, 10A, UPF
(0-10)A
MI
Fuse
P
230V,
1 AC
Supply
S
W
I
T
C
H
15A
L
C
V
M1
Auto Transformer
230/(0-270) V
D
P
S
T
M
A
V
C
S1 S2
Kg Kg
(0-300)V
MI
M2
Rotor
Brake Drum
N
Link
S1
S2
FUSE RATING:
NAME PLATE DETAILS:
125% of rated current
Rated Voltage
Rated Current
Rated Power
Rated Speed
125 x 9.5
---------------100
= 15 A
:
:
:
:
220V
9.5A
3HP
1470 RPM
S1, S2- AUXILLARY WINDING
M1, M2- MAIN WINDING
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
1
VOLTMETER
2
AMMETER
3
WATTMETER
4
TACHOMETER
SPECIFICATIONS
(0-600V) MI
(0-5A) MI
(600V,10A,UPF)
(0-10000 RPM)
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)
2NT
4. Output power =
(watts)
60
output power
5. % Efficiency (η) =
x100
input power
W  W2
6. Power factor, Cos Φ = 1
3 VI
Cos Φ= Power factor
7. %Slip, s =
Ns  N
 100
Ns
NS = synchronous speed =
P = no. of poles
f=frequency of supply (Hz)
120 f
(rpm)
P
QUANTITY
1
1
2
1
PRECAUTIONS:
1. The motor is started at no load condition.
PROCEDURE:
1. Connections are given as per the circuit diagram
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)
W1
W2
W1+W2
Obs Act Obs Act
Spring
balance Torque
readings (Kg)
(T)
N-m
S1
S2
S1~S2
Output
power
(Watts)
Power
factor
(cos Φ)
%
efficien
cy
(η)
% Slip
(s)
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:
SI.NO
1
APPARATUS
VOLTMETER
SPECIFICATIONS
(0-600V) MI, (0-300V)MI
2
AMMETER
(0-10A) MI, (0-5ª)MI
2
3
WATTMETER
(300V,10A,UPF)
(600V,5A,LPF)
2
2
FORMULAE:
NO LOAD TEST:
W0
Cos Φ0 =
3  V0  I 0
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
Ro=
V0 ( ph)
Iw
=
Iµ= Io Sin Φ0
Amps
V0
3  Iw
Ω
Amps
QUANTITY
2
V0 ( ph)
Xo=
I
V0
=
3  I
BLOCKED ROTOR TEST:
V
ISN = I SC
VSC
I
WSN= Wsc   SN
 I SC
Cos Φsc =
2

 (watts)

WSC
3  Vsc  Isc
X01= Z 01  R01 ()
2
R2’ = R01/ 2
RL’ = R2’
1 s
s
2
Ω
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)
Ω
PROCEDURE:
NO LOAD TEST:
1. Connections are given as per the circuit diagram
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:
1. Connections are given as per the circuit diagram
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
I0
(volts)
(amps)
W1
(watts)
W2
(watts)
W0
(watts)
W2
(watts)
WSC
(watts)
BLOCKED ROTOR TEST
VSC
ISC
(volts)
(amps)
W1
(watts)
MODEL EQUIVALENT CIRCUIT:
MODEL GRAPH:
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
Rated Voltage :
415V
Rated Current :
4.5A
Rated Power :
3HP
Rated Speed :
1440 RPM
rotor
185V
7.5A
BLOCKED ROTOR TEST:
FUSE CALCULATION:
1.25*4.5= 10A
NAME PLATE DETAILS:
Stator
Rated Voltage :
415V
Rated Current :
4.5A
Rated Power :
3HP
Rated Speed :
1440 RPM
rotor
185V
7.5A
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
BG Rotor copper loss

GD Stator copper loss
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
WSN
Power scale =
 W / cm
 ( BE )
 (BE) = Distance BE in cm
Location of point E (slip ring induction motor):
I
K = 1 = transformation ratio
I2
AE Rotor copper loss I 22 R2 R2



EF stator copper loss I 12 R1 R1
R21 
 I2

 I1



2
R2
= Rotor resistance referred to stator.
K2
BG R21

GD R1
Thus pt G can be obtained by dividing the line BD in the ratio R2' R1
Location of point D (squirrel cage induction motor):
In a squirrel cage motor, the stator resistance can be measured by conducting resistance test.
2
i.e., Stator copper loss = 3I SN
R1 where I SN is phase value.
Neglecting core loss, WSN = stator Cu loss + Rotor Cu loss
2
R1
i.e., Rotor copper loss = WSN  3I SN
BG WSN  3 2SN R1

2
GD
3I SN
R1
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.
12.
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.
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:
SI.NO
1
2
3
4
APPARATUS
VOLTMETER
AMMETER
RHEOSTAT
TACHOMETER
SPECIFICATIONS
(0-300V) MI
(0-5A) MI
300Ω,1.2A
(0-10000 RPM)
QUANTITY
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:
1. Connections are given as per the circuit diagram
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:
SI.NO
1
2
3
4
APPARATUS
VOLTMETER
AMMETER
RHEOSTAT
TACHOMETER
SPECIFICATIONS
(0-600V) MI
(0-5A) MI
300Ω,1.2A
(0-10000 RPM)
QUANTITY
2
1
1
1
FORMULAE:
EMF METHOD:
Synchronous impedance, Zs =
OC voltage / phase
(at constant If)
SCcurrent / phase
Synchronous reactance, Xs = Zs 2  Rac 2 ()
Where Rac = armature resistance
For rated conditions,
EMF, E0 = (Vph cos   IRa ) 2  (Vph sin   IXs ) 2
+ corresponds to lagging power factor
- corresponds to leading power factor
% Regulation =
E 0  Vph
x100
Vph
MMF METHOD:
If1 = field current corresponding to Isc
E = Vph + IRa cosΦ
If2 = field current corresponding to E from graph
If0 = ( If 12  If 2 2  2If 1 If 2 cos(180  (90   ))
E0 = open circuit voltage corresponding to If0 (from graph)
% Regulation =
E 0  Vph
x100
Vph
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:
1.
2.
3.
4.
5.
6.
Connections are given as per the circuit diagram
The TPST switch of the alternator is kept opened.
The DPST-1 switch is closed
The motor field rheostat is varied such that the alternator runs at rated speed.
The DPST-2 switch is closed.
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:
1.
2.
3.
4.
5.
6.
Connections are given as per the circuit diagram
The DPST-1 switch is closed
The motor field rheostat is varied such that the alternator runs at rated speed.
The TPST switch is closed.
The DPST-2 switch is closed.
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
S.C.CURRENT
CURRENT(If)( (ISC)(amps)
amps)
EMF METHOD:
cos Ø
E0(volts)
LAG
LEAD
% regulation
LAG
LEAD
Unity
MMF METHOD:
cos Ø
E0(volts)
LAG
Unity
LEAD
% regulation
LAG
LEAD
MODEL GRAPH:
CIRCUIT DIAGRAM: REGULATION OF THREE PHASE ALTERNATOR BY EMF AND MMF METHODS
10A
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:
SI.NO
1
2
3
4
5
APPARATUS
VOLTMETER
AMMETERS
RHEOSTAT
TACHOMETER
REACTIVE LOAD
SPECIFICATIONS QUANTITY
(0-600V) MI
1
(0-5A) MI
1
(0-10A)MI
1
300Ω,1.2A
2
(0-10000 RPM)
1
(1-15) amps
1
FORMULAE:
EMF, E1 = (Vph cos   IRa ) 2  (Vph sin   IX L ) 2
+ 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 = ( If 12  If 2 2  2If 1 If 2 cos(180  (90   ))
E0 = open circuit voltage corresponding to If0 (from graph)
% Regulation =
E 0  Vph
x100
Vph
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
PHASE
VOLTAGE(VL) VOLTAGE
(volts)
(Vph)(volts)
SC TEST:
FIELD
CURRENT(If)
(amps)
S.C.CURRENT
ISC(amps)
ZPF TEST:
If(amps)
VZPF(VOLTS)
ISC(amps)
ZPFMETHOD:
cos Ø
E0(volts)
LAG
Unity
MODEL GRAPH:
LEAD
% regulation
LAG
LEAD
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
1.25*10=15A
ALTERNATOR
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:
SI.NO
1
2
3
4
APPARATUS
VOLTMETER
AMMETERS
RHEOSTAT
WATTMETER
SPECIFICATIONS
(0-600V) MI
(0-2A) MC
(0-10A)MI
300Ω,1.2A
600V,10A,UPF
QUANTITY
1
1
1
1
2
FORMULAE:


 W  W2
Φ = cos tan 1  3   1

 W1  W2


  
 

  
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
Amps
If
Amps
MODEL GRAPH:
V
Volts
W1(watts)
OBS
ACT
W2(watts) W1+W2(watts)
OBS ACT
COSΦ
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:
SI.NO APPARATUS
1
VOLTMETER
2
AMMETERS
RHEOSTAT
3
SYNCHRONISING LAMPS
SPECIFICATIONS
(0-600V) MI
(0-2A) MC
300Ω,1.2A
350Ω,2A
230V,15A
QUANTITY
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:
SI.NO
1
2
3
APPARATUS
Voltmeter
Ammeter
Tachometer
SPECIFICATIONS
(0-600V) MI
(0-10A) MI
0-10000 (rpm)
QUANTITY
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
Current (A)
(V)
Resistance ()
Speed (rpm)
MODEL GRAPH:
1480
1460
1440
1420
1400
1380
1360
1340
1430
1440
1450
1460
resistance(ohm)
5.
88
12
.1
2
21
.8
32
.2
46
.6
)
(W
ta
nc
e
1470
Speed (rpm)
1390
Re
sis
speed(rpm)
Speed vs resistance
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:
SI.NO
1
2
3
4
5
APPARATUS
Voltmeter
Ammeter
Tachometer
Frequency meter Digital
. Rheostat Wire Wound
SPECIFICATIONS
(0-600V) MI
(0-10A) MI
(0-2)A MC
0-10000 (rpm)
(0-60Hz)
300Ω, 1.2A
QUANTITY
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 noload.
TABULATION
Induction motor on no load
Line voltage
In volts
Frequency
In Hz
Speed of IM
In rpm
MODEL GRAPH:
CIRCUIT DIAGRAM: SPEED CONTROL OF INDUCTION MOTOR BY VARIABLE FREQUENCY METHOD
Fuse calculation:
125% of Rated current=1.25*19=30A
NAME PLATE DETAILS:
Motor
Rated Voltage
Rated Current
Rated Power
Rated Speed
:
:
:
:
220V
19A
3HP
1500 RPM
Alternator
415V
4.2A
5KVA
1500 RPM
RESULT:
POSTLAB QUESTIONS:
1.