3 Experiments
3 Experiments
3 Experiments
OBJECTIVE:
Electrical Machines Laboratory-II explores all the possible design connections of an AC
machines like Transformers, Induction & Synchronous and it also experimentally obtains the
characteristics and thus observes the performance of AC motors and generators.
At the completion of this lab, the student will be able to:
Obtain the operating characteristics of AC machines.
Examine the relationship between torque, speed, voltage and current for various types of
motor connections in no-load and loaded configurations.
Predict, by calculation, the performance of Transformers and Synchronous Generators.
Analyze and select appropriate AC machines for given applications.
List of Experiments
Cycle-I:
Cycle-II:
Circuit Diagram:
APPARATUS REQUIRED:
Name of the
S.No. Range Type Quantity
Apparatus
(0-2) A MI 1
1 Ammeter
(0-20) A MI 1
(0-75) V MI 1
2 Voltmeter
(0-150)V MI 1
150V, 2A, LPF DM 1
3 Watt meter
75V, 20A, UPF DM 1
4 1- Auto-Transformer 230V/(0-270)V,10A Wire Wound 1
3KVA,
5 1- Transformer Shell 1
230V/115V, 50Hz
required
6 Connecting wires --- ---
number
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. Use LPF type wattmeter for OC test and UPF type wattmeter for SC test.
3. The auto-transformer should be kept in minimum position initially.
4. The auto-transformer should be varied slowly and uniformly.
PROCEDURE:
OC Test:
1. Make the connections as per circuit diagram.
2. Keep the autotransformer in zero output voltage position and close the DPST switch.
3. Vary the autotransformer variable knob and apply rated voltage across LV winding of the 1-
ϕ Transformer.
Circuit Diagram:
4. Note the values of no load current, no load voltage and input power.
5. Bring back the auto transformer to zero output voltage position and open DPST to
disconnect the circuit.
SC Test:
1. Make the connections as per circuit diagram.
2. Keep the autotransformer in zero output voltage position and close the DPST switch
3. Vary the autotransformer variable knob and allow rated current through HV winding of the
1- Transformer.
4. Note the values of short circuit current, voltage and input power.
5. Bring back the auto transformer to zero output voltage position and open DPST to
disconnect the circuit.
Calculations:
For Open circuit test:
WOC = VOC IOC CosΦOC
WOC
Cos 0C
=
VOC I OC
I O Sin
Im = OC
I O CosOC
IW =
VOC
Shunt branch resistance, Ro =
IC
VOC
Shunt branch reactance, Xo =
Im
For Short circuit test:
Wsc Isc 2 R01
X012 = Z012 –R012 Where X01 is total Eq. reactance referred to HV Side
I 2 R cos I 2 X 02 Sin
%Regulation = 02
*100 Where Cos = P.F of load
V2
o/P
% = X 100 ( i/P = o/p + Total Losses)
i/ p
TABULAR COLUMN:
OC Test:
SC Test:
To Find % Efficiency
O/P
Cu losses Iron losses Total losses I/P power %η
S. No. Loading power
(W) (W) (W) (W) (%)
(W)
1 N.L
2 ¼ F.L
3 ½ F.L
4 ¾ F.L
5 F.L
To Find % Regulation
0.4 (lag)
0.6 (lag)
0.8 (lag)
unity
0.4 (lead)
0.6 (lead)
0.8 (lead)
SAMPLE CALCULATION:
MODEL GRAPH:
Efficiency Characteristics
%Efficiency (%)
Regulation Characteristics
Regulation
% Voltage
Leading Lagging
Power Factor
APPLICATIONS:
RESULT:
Circuit Diagram:
Expt. No:
Date:
SUMPNER’s TEST ON A PAIR OF 1-ϕ TRANSFORMERs
AIM: To conduct Sumpner’s test on a pair of identical single-phase transformers and to determine
efficiency and regulation at different loads for a given power factor.
NAME PLATE DETAILS:
APPARATUS REQUIRED:
Name of the
S.No. Range Type Quantity
Apparatus
(0-5) A MI 1
1 Ammeter
(0-10) A MI 1
(0-75) V MI 1
2 Voltmeter (0-150)V MI 1
(0-600)V MI 1
150V, 2A, LPF DM 1
3 Watt meter
75V, 10A, UPF DM 1
4 1- Auto-Transformer 230V/(0-270)V,10A Wire Wound 2
2KVA,
5 1- Transformer Shell 2
230V/115V, 50Hz
required
6 Connecting wires --- ---
number
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. The auto-transformer should be kept in minimum position initially.
3. The auto-transformer should be varied slowly and uniformly.
4. SPST should be closed only when voltmeter connected across it shows zero reading.
PROCEDURE:
1. Make the connections as the circuit diagram.
2. Close the DPST switch and make sure that SPST connected on secondaries of transformers
are in open.
TABULAR COLUMN:
Transformer-1 Transformer-2
W1 W2
V1 (Volts) I1 (Ampere) V2 (Volts) I2 (Ampere)
(Watts) (Watts)
To Find % Efficiency
O/P
Cu losses Iron losses Total losses I/P power %η
S. No. Loading power
(W) (W) (W) (W) (%)
(W)
1 N.L
2 ¼ F.L
3 ½ F.L
4 ¾ F.L
5 F.L
To Find % Regulation
0.4 (lag)
0.6 (lag)
0.8 (lag)
unity
0.4 (lead)
0.6 (lead)
0.8 (lead)
3. Apply rated voltage on LV side by adjusting the variable knob of 1-ϕ auto-transformer-1.
4. Note down readings of all meters connected on the LV Side.
5. If the volt meter connected across two secondary windings of transformers reads zero
voltage then close SPST switch, otherwise interchange the any one of the secondary winding
for series opposition.
6. Apply rated current on HV side of transformers by adjusting the variable knob of 1-ϕ auto-
transformer-2.
7. Note down readings of all meters connected on the HV Side.
8. Bring back the two auto transformers to zero output voltage position and open DPST to
disconnect the circuit.
CALCULATIONS
For Efficiency:
For Regulation:
Reh=Wsc / Isc2 (Where Wsc =W2 / 2 ) and Zeh= Vsc / Isc (Where Vsc= V2 / 2 & Isc= I2)
I HV R eh Cos X xh Sin
% regulation =
VHV
SAMPLE CALCULATIONS
MODEL GRAPH:
Efficiency Characteristics
%Efficiency (%)
Regulation Characteristics
Regulation
% Voltage
Leading Lagging
Power Factor
Sumpner’s test is much improved method of predetermining regulation and efficiency than OC
and SC tests.
The Sumpner's test requires two identical transformers.
Thus in the sumpner's test without supplying the load, full iron loss occurs in the core while full
copper loss occurs in the windings simultaneously. Hence heat run test can be conducted on the
two transformers. In OC and SC test, both the losses do not occur simultaneously hence heat run
test cannot be conducted. This is the advantage of Sumpner's test.
APPLICATIONS:
RESULT:
Circuit Diagram:
Expt. No:
Date:
SCOTT CONNECTION OF TRANSFORMERS
AIM: To obtain balanced two phase supply from balanced three phase supply by connecting two 1-
transformers in Scott connection
NAME PLATE DETAILS:
APPARATUS REQUIRED:
Name of the
S.No. Range Type Quantity
Apparatus
(0-600) V MI 1
1 Voltmeter
(0-150)V MI 2
2 3- Auto-Transformer 415V/(0-470)V,10A Wire Wound 1
3KVA,
3 1- Transformer Shell 1
230V/115V, 50Hz
required
4 Connecting wires --- ---
number
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. The auto-transformer should be kept in minimum position initially.
3. The auto-transformer should be varied slowly and uniformly.
PROCEDURE:
1. Make the connections as per circuit diagram.
2. TPST Switch is kept in open position & autotransformer is kept in zero output voltage
position initially.
3. Close the TPST switch, adjust the variable knob of 3- auto-transformer in steps and
increase the voltage applied. Note down secondary side voltmeter readings V2, V3 & primary
voltmeter reading V1 in each step.
4. Applied voltage is increased until the secondary voltage (V3) of main transformer reaches its
rated value.
TABULAR COLUMN:
SAMPLE CALCULATIONS:
5. Autotransformer is brought to minimum output voltage position & the TPST switch is
opened.
There are two main reasons for the need to transform from three phases to two phases,
To give a supply to an existing two phase system from a three phase supply.
To supply two phase furnace transformers from a three phase source.
If desired, a three phase, two phase, or single phase load may be supplied simultaneously
The neutral points can be available for grounding or loading purposes
APPLICATIONS:
RESULT:
Circuit Diagram:
Expt. No:
Date:
PARALLEL OPERATION OF 1-ϕ TRANSFORMERS
AIM: To connect two 1- transformers in parallel to load and check the load sharing of each
transformer.
NAME PLATE DETAILS:
APPARATUS REQUIRED:
Name of the
S.No. Range Type Quantity
Apparatus
1 Voltmeter (0-300) V MI 1
(0-10)A MI 2
2 Ammeter
(0-20)A MI 1
3 1- Auto-Transformer 230V/(0-270)V,10A Wire Wound 1
2 KVA,
4 1- Transformer Shell 2
230V/115V, 50Hz
5 Resistive Load 5 KW Wire Wound 1
required
6 Connecting wires --- ---
number
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. The auto-transformer should be kept in minimum position initially.
3. The auto-transformer should be varied slowly and uniformly.
4. Adjust the measuring instruments for zero error.
5. The condition for Parallel Operation should be strictly established before transformers are
operated
PROCEDURE:
Polarity Test:
1. Connect the primaries of two identical transformers in parallel and secondary’s on open
circuit for polarities of the windings by a voltmeter of double range of normal secondary
voltage.
TABULAR COLUMN:
Secondary Secondary
Supply Load
Applied Current of Current of
Voltage Current
Load Transformer-1 Transformer-2
V (V) IL (A)
I1 (A) I2 (A)
SAMPLE CALCULATIONS:
2. If the voltmeter reads double the secondary voltage then it is concluded that opposite
polarities have been connected.
3. If the voltmeter reads zero voltage then it is concluded that same polarities have been
connected.
4. This test is necessary for secondary windings only.
Parallel Operation:
1. When voltage polarities have been find out completely then give the connections as per
circuit diagram.
2. Switch on the supply and gradually increase the 1- auto-transformer to rated voltage of the
transformer.
3. Now apply the load in steps up to rated current of the transformer and at each step the
voltage should be maintained constant.
4. Note down the readings of voltmeter & ammeters.
5. After taking the readings remove load and bring the 1- auto-transformer to zero position.
6. Switch off the supply.
Necessary Conditions:
Sufficient Conditions:
Synchroscope:
To Main
Rotor Wound
Bus-Bar
for two phases
To
Incoming Stator Wound
Machine for two phases
SYNCHROSCOPE
A synchroscope is an instrument for indicating the correct time for switching on. For operation
of large machines, it is a suitable device. It consists of a small motor with stator and rotor
windings of both wound for two phases.
Its working is based on the rotating magnetic field principle.
The pointer position of the synchroscope indicates the phase difference between the voltages of the
incoming machine and the infinite bus.
When the frequencies are equal, the pointer is stationary. When the frequencies differ, the pointer rotates
in one direction or other.
The direction of motion of the pointer shows whether the incoming machine is running too fast or too
slow, that is whether the frequency of the incoming machine is higher or lower than that of the infinite
bus.
APPLICATIONS:
RESULT:
Circuit Diagram:
AIM: To determine the voltage regulation of a given alternator by synchronous impedance method
and mmf method.
APPARATUS REQUIRED:
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
TABULAR COLUMN
Open Circuit test:
Open Circuit
Open Circuit
Field Current Voltage
Voltage
S.No. If (Ph)
(L-L)
(Amps) Eoc/Ph=
Eoc (Volts)
Eoc/L/√3 (Volts)
%Voltage
Regulation=
Eg= (V cos I a Ra ) 2 (V sin I a X S ) 2 Eg V
S.No. cosϕ sinϕ
*100
V
Lagging Leading Lagging Leading
PROCEDURE:
1. Make the connections as per circuit diagram.
2. Close the DPST switch and start the motor using 3-point starter with minimum resistance of
motor rheostat.
3. Adjust the motor field rheostat till the rated speed of the generator is achieved.
4. To Conduct OC Test, excite the alternator field rheostat in steps till the alternator builds up
to 125% of its rated voltage and note down the corresponding values of no-load generated
emf and the shunt field current.
5. Again keep the alternator field rheostat in maximum position.
6. To Conduct SC Test, close the TPST switch on alternator terminal side.
7. Excite the alternator field rheostat in steps till the alternator reaches to its rated current /
short circuit current and note down the corresponding value of the field current.
8. Again keep the alternator field rheostat in maximum position, Open the TPST switch.
9. Keep the motor filed rheostat in minimum position and open the DPST switch.
10. Plot the Open Circuit Characteristic (OCC) curve between field current (vs) no-load
generated emf and Short Circuit Characteristic (SCC) curve between field current (vs) rated
current / short circuit current.
MODEL GRAPH:
EMF METHOD
SAMPLE CALCULATIONS:
Consider terminal voltage (V) as a reference, load current (Ia) leads terminal voltage ‘V’
by an angle ‘∅ ‘.
2
Eg = (V cos ∅ + Ia Re)2 + V sin ∅ - Ia Xs
Eg - V
% Voltage regulation = × 100 about 30%
V
Va Ia Ra
S.No.
(Volts) (Amps) (Ω)
Average Resistance
MMF METHOD
Ifm is the main field current required to generate rated induced emf under Open-Circuit condition
Ifr is the main field current required to produce the armature or full load current under Short-
Circuit Condition
Ift is the main field current which gives the maximum open circuit induced EMF
Ift , Ifm and Ifr are also represented in terms of ∅fm , ∅fr and ∅ft respectively.
Calculation or estimation of regulation of the machine without actually loading the machine, by
using indirect methods is known as predetermination of regulation.
The value of voltage regulation estimated by EMF method is always higher or poor than the actual value
and hence this method is called pessimistic method.
The value of voltage regulation estimated by MMF method is always lower than the actual value and
hence this method is called optimistic method.
In EMF method all the MMFs are replaced by emf for voltage regulation where as in MMF method all
the emfs are replaced by mmfs for voltage regulation.
APPLICATIONS:
RESULT:
Circuit Diagram:
AIM: To determine Xd and Xq of a 3- phase salient pole alternator by conducting slip test.
APPARATUS REQUIRED:
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
PROCEDURE:
1. Make the circuit as shown in circuit diagram.
2. Keep Shunt motor field regulator in minimum resistance position and TPST in open position
3. Close the DPST switch and start the DC motor. Adjust its speed to the speed slightly less than
the rated speed with the help of field rheostat.
TABULAR COLUMN:
SAMPLE CALCULATION:
4. If the voltmeter across the field reads twice the rated voltage, then change the phase sequence
(such that the voltmeter reads zero)
5. Close TPST switch and apply 25% of rated voltage to the alternator stator by adjusting 3-phase
Autotransformer.
6. Introduce some slip by varying the speed of alternator till the fluctuations in the voltmeter and
ammeter are maximum.
7. Note down the maximum and minimum values of currents and voltages (Vmax, Vmin, Imax, Imin) in
the armature circuit.
8. Calculate Xd and Xq using Xd = Vmax / Imin (per phase) and Xq = Vmin /Imax (per phase).
9. Repeat the above procedure for different values of applied voltage to the alternator. Take the
average of all the values of Xd and Xq.
APPLICATIONS:
RESULT:
Circuit Diagram:
Expt. No:
Date:
BRAKE TEST ON 3-ϕ INDUCTION MOTOR
AIM: To conduct brake test on 3- Induction Motor and to determine its performance characteristics.
1 Rated Voltage
2 Rated Current
3 Rated Power
4 Rated Speed
5 Rotor type
APPARATUS REQUIRED:
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. The auto-transformer should be kept in minimum position initially.
3. The auto-transformer should be varied slowly and uniformly.
4. Adjust the measuring instruments for zero error.
PROCEDURE:
1. Connect the circuit as per the diagram and taking care that the brake belt is loose and the
brake drum is filled with water for cooling.
2. Start the motor and note down the readings of ammeter, wattmeter and the speed of the
motor in the table.
TABULAR COLUMN:
Applied Load Speed Spring Fields Input Torque Output Power % Efficiency
S=S1-S2 2πNT Po/p
S. No. Voltage Current IL N S1 S2 Power Pi/p T=9.81*S*r
(Kg) Po/p = (W) η= *100 (%)
(V) (A) (rpm) (Kg) (Kg) (W) (N-m) 60 Pi/p
3. Load the motor by tightening the brake belt in steps up to full load (the full load current read by
the ammeter).
4. Note down the readings as per tabular column.
5. Plot the performance characteristics of the motor.
SAMPLE CALCULATIONS:
MODEL GRAPH:
%Efficiency (%)
Torque (N-m)
Speed
Speed (rpm)
Efficiency
Torque
APPLICATIONS:
RESULT:
Circuit Diagram:
AIM: To plot the circle diagram of the 3- induction motor to determine its slip, Torque, output,
efficiency at full load, maximum Torque, slip at maximum torque, starting torque by conducting no
load and blocked rotor test.
1 Rated Voltage
2 Rated Current
3 Rated Power
4 Rated Speed
5 Rotor type
APPARATUS REQUIRED:
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. The auto-transformer should be kept in minimum position initially.
3. The auto-transformer should be varied slowly and uniformly.
4. Adjust the measuring instruments for zero error.
5. Increase the applied voltage slowly & carefully in blocked rotor test.
Circuit Diagram:
PROCEDURE:
No load Test:
1. Tight the belt around the brake drum to block the rotor of induction motor.
2. The applied voltage is increased slowly by varying 3- autotransformer variable knob until the
ammeter reads rated current.
3. Note down Voltmeter (Vsc), ammeter (Isc) & wattmeter (Wsc) reading.
4. Bring the 3- autotransformer to zero output voltage position and open the supply TPST switch.
Circle diagram:
Locating point D:
Power input to motor blocked rotor test, stator copper loss = 3Isc2 R1
D is located such that AD/DE= Rotor copper loss/ Stator copper loss.
K may be found by connecting two ammeters one in stator circuit & other in rotor circuit in
blocked rotor test.
SAMPLE CALCULATIONS:
TABULAR COLUMN:
No-Load Test:
No-Load No-Load P0
No-Load Power ϕ0 = cos-1
Voltage Current W1(W) W2(W)
P0= W1+ W2 (W) √3 V0 I0
V0 (Volts) I0 (Amp)
The Circle diagram provides information which is not provided by an ordinary phasor diagram.
A phasor diagram gives relation between current and voltage only at a single circuit condition. If
the condition changes, we need to draw the phasor diagram again.
But a circle diagram may be referred to as a phasor diagram drawn in one plane for more than
one circuit conditions. Therefore, we can get information about its power output, power factor,
torque, slip, speed, copper loss, efficiency etc. in a graphical or in a diagrammatic
representation.
The circle diagram of an induction motor is very useful to study its performance under all
operating conditions.
APPLICATIONS:
RESULT:
Circuit Diagram:
Expt. No:
Date:
EQUIVALENT CIRCUIT OF AN 1-ϕ INDUCTION MOTOR
AIM: To determine the equivalent circuit parameters of a single phase induction motor by
conducting No-Load and Blocked rotor tests.
1 Rated Voltage
2 Rated Current
3 Rated Power
4 Rated Speed
5 Rotor type
APPARATUS REQUIRED:
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. The auto-transformer should be kept in minimum position initially.
3. The auto-transformer should be varied slowly and uniformly.
4. Adjust the measuring instruments for zero error.
Circuit Diagram:
PROCEDURE:
No-Load Test:
Equivalent Circuit:
Determine r1, r21, x1 and x21 from the test data given above.
When the rotor is blocked, S=1 and X0/2 is much larger than the impedance in parallel with it.
Therefore the equivalent circuit reduces to the one shown below.
RSC = r1 + r21 = WSC / ISC2 = 2 r1 =2 r21 because in all the machines
2 2
XSC= x1 + x21 = ( Z SC R SC )=2 x1 =2 x21
No Load Test:
At no load S is very small hence r21/2S is very large as compare to X0/2. More over r21/ 2 ( 2 – S) =
r21/ 4r21/ 4 + r21/ 4 + JX21/ 2 is very small as compared to X0/2.
The shunt branch resistance R0 is neglected. Therefore under no load condition the equivalent circuit
becomes as shown below
R1, R21, X1 and X21 are known from blocked rotor test.
TABULAR COLUMN:
No-Load Test:
SAMPLE CALCULATIONS:
Calculation of Xm:
1 1
Vab V0 I 0 0 (r1 r2 /4) (X1 X 2 /2)
Since r1, r21, X1 and X21 are known from blocked rotor test.
EQUIVALENT CIRCUIT
APPLICATIONS:
RESULT:
Circuit Diagram:
AIM: To conduct suitable test to plot ‘V’ and ‘Inverted V’ curves of a given Synchronous Motor.
1 Rated Voltage
2 Rated Current
3 Rated Power
4 Rated Speed
APPARATUS REQUIRED:
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
2. The starter should be kept in position-1 initially.
3. Adjust the measuring instruments for zero error.
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. The resistance in the field circuit of motor is kept at minimum position to stud-1.
3. Close the TPST Switch, start the synchronous motor starter making the starter position to
stud-1.
4. Then make the starter position to stud-2, varying knob of starter and note down the readings
of voltmeter, ammeter & wattmeter.
TABULAR COLUMN:
SAMPLE CALCULATIONS:
5. By varying the variable rheostat from maximum to minimum position, note down the
readings.
6. Brought the field rheostat to minimum position, synchronous motor starter to the initial
position and switch-off the supply.
7. Plot the curves, field current versus armature current and power factor.
MODEL GRAPH:
‘V’ Curve:
‘Inverted-V’ Curve:
Power Factor
APPLICATIONS:
RESULT:
Circuit Diagram:
AIM: To determine the voltage regulation of a given alternator by zero power factor method and
ASA method.
APPARATUS REQUIRED:
PRECAUTIONS:
1. Avoid loose connections and parallax error while taking the readings.
Circuit Diagram:
PROCEDURE:
1. Make the connections as per circuit diagram.
2. Close the DPST switch and start the motor using 3-point starter with minimum resistance of
motor rheostat.
3. Adjust the motor field rheostat till the rated speed of the generator is achieved.
4. To Conduct OC Test, excite the alternator field rheostat in steps till the alternator builds up
to 125% of its rated voltage and note down the corresponding values of no-load generated
emf and the shunt field current.
5. Again keep the alternator field rheostat in maximum position.
6. To Conduct SC Test, close the TPST switch on alternator terminal side.
7. Excite the alternator field rheostat in steps till the alternator reaches to its rated current /
short circuit current and note down the corresponding value of the field current.
8. Again keep the alternator field rheostat in maximum position, Open the TPST switch.
9. Keep the motor filed rheostat in minimum position and open the DPST switch.
10. Plot the Open Circuit Characteristic (OCC) curve between field current (vs) no-load
generated emf.
11. To obtain ZPF, make the connections as per the 2nd circuit diagram and follow the points
same as 2, 3.
12. Now close the TPST switch, vary the 3-ϕ Inductive load & field rheostat such that obtain the
condition that the rated terminal voltage, armature current and field current is achieved and
disconnect the circuit.
13. Tabulate the readings and plot the zpf curve
TABULAR COLUMN:
Open Circuit test:
%Voltage
Regulation=
Eg= (V cos I a Ra ) 2 (V sin I a X S ) 2 Eg V
S.No. cosϕ sinϕ
*100
V
Lagging Leading Lagging Leading
(i.e., Ifr)
‘OA’ represents field current which is equal and opposite to the demagnetizing armature
reaction and balancing leakage reactance drop at full-load.
4. By knowing ‘P’ and ‘A’ points, the full-load curve at zero power factor ‘A P’ is drawn.
5. From ’P’, PQ is drawn equal to and parallel to OA. From point –‘Q’, QR is drawn parallel to
OE i.e., tangential or air-gap line. Hence we get ‘R’ point on No-Load or OCC curve, which
corresponds to point ‘P’ on full-load zero power factor curve. The triangle ‘∆PRS’ called
known as potier triangle. This triangle is constant for a given armature current.
6. Draw RS perpendicular to PQ. The length RS represents the drop in voltage due to armature
leakage reactance XL.
i.e., RS = IXL & PT = Ia(Xa + X L)
Ift1 = field current to compensate drop due to saturation and is added in phase with Ift
Measure ‘E0’ corresponding to Ift1 .
MODEL GRAPH:
Va Ia Ra
S.No.
(Volts) (Amps) (Ω)
Average Resistance
SAMPLE CALCULATIONS:
APPLICATIONS:
RESULT:
Circuit Diagram:
APPARATUS REQUIRED:
Name of the
S.No. Range Type Quantity
Apparatus
1 Voltmeter (0-300)V MI 1
2 Watt meter 300V, 5A, LPF DM 1
3KVA,
3 1- Transformer Shell 1
230V/115V, 50Hz
4 Rheostat 300Ω/2A wire wound 1
5 Potential divider 850Ω/0.6A wire wound 1
6 Tachometer (0-3000)rpm Digital 1
required
7 Connecting wires --- ---
number
PRECAUTIONS:
1. Avoid the loose connections.
2. Avoid parallax error while taking the readings.
3. Keep the field rheostat in the minimum resistance position
4. Keep the potential divider, alternator field rheostat in maximum voltage output position.
PROCEDURE:
1. Connect the circuit as per the circuit diagram.
2. Initially keep both the rheostats connected in series with the field winding and armature of
DC motor in minimum resistance position.
TABULAR COLUMN:
Iron losses
Speed Frequency V/F No Load
Voltage per cycle
S.No. N F=PN/120 Ratio Power
(Volts) WO/F
(rpm) (Hz) (v/rpm) WO (watts)
(W/Hz)
MODEL GRAPHS:
SAMPLE CALCULATIONS:
APPLICATIONS:
RESULT:
VIVA QUESTIONS
Transformers:
1. Which losses are called magnetic losses?
2. Write equations for hysteresis and eddy-current losses?
3. What are the conditions for maximum efficiency in a transformer?
4. Explain why low power factor meter is used in O.O. test?
5. Why iron losses are neglected when S.C test on a Transformer?
6. What are the advantages of Sumpner’s test?
7. Draw the phasor diagram for a S.C. test on a transformer?
8. How do you reduce the hysteresis and eddy-current losses?
9. ls the transformer core laminations are insulated? Why?
10. Represent the step up and step down transformer?
11. Draw the equivalent circuit of a transformer?
12. Why transformer efficiency is more than an induction motor?
13. Write equations for emf of a transformer?
14. What is the magnitude of no-load current?
15. What is the function of an auto-transformer?
16. What happens to Transformer when DC supply is given?
17. How do you mark dot on a transformer?
18. Does flux in a transformer changes with load?
19. Why transformer no-load current is a small value in spite of its primary impedance is very
small?
20. A transformer is designed for 50Hz. lf the supply frequency is 60 Hz. What is the change in
its performance?
21. A transformer has primary more than secondary turns. ls it step-down or step-up
transformer?
22. How do you identify core-type of transformer?
23. One transformer has cruciform type and second transformer has square type of core which is
the better one?
24. Define voltage regulation with equation for lagging and leading loads.
25. Draw the phasor diagrams for leading and lagging loads.
26. For a step-down transformer which winding has low resistance?
27. Draw the phasor diagram for lagging load.
28. What are the conditions required to parallel two transformers?
29. What is the full name of C.R.G.O.S. core material?
30. Generally what is the efficiency percentage of a transformer?
31. What is the role of Buchholz relay?
32. What is the material kept inside a breather?
33. Write the relations between line-currents, phase-currents and line, phase voltages in a star
and delta connections.
34. What is the use of Scott connection?
35. Compare open delta, Scott connections
36. Draw the phasor diagram for Scott connection.
37. Draw star/star, star/delta, delta/star, delta/delta winding connections when three single phase
transformers are used.
38. What is the use of tertiary winding in a transformer?
39. How can you use a 3-phase auto-transformer as a step-up autotransformer?
1. How do you connect the six terminals of the motor as Delta or Star?
2. What are the different starting methods used?
3. What is the role of a rotating flux?
4. How do you change the direction of rotation?
5. Why star point of the motor is not connected to neutral point of the Supply?
6. Does the motor start when supply lines are connected?
7. For a two-phase supply waveform & leading current, lagging current with respect to the
voltage.
8. Draw the Three-phase supply waveform& leading current, lagging current with respect to the
voltage.
9. What is the advantage of star delta starter when compared to, D.O.L. starter?
10. For a 6-pole machine what is the value of synchronous speed?
11. Why slip cannot be zero in induction motor?
12. What are the two different types of rotors?
13. Why one spring balance always indicate zero in a load test?
14. When one phase is removed in a three-phase supply it is called single phase supply instead
of two-phase supply. Why?
15. Draw the Torque-slip, Torque-speed characteristics of a wound rotor motor and mark stable
and unstable area.
16. What is the relation between Torque and voltage?
17. Is it possible to get speed control from zero to rated speed in an induction motor?
18. Why do we say that induction motor is similar to DC shunt motor characteristic?
19. lf one phase flux is from a three phase running motor, does it continue to rotates or stops?
20. Which type of motor is used to start with load?
21. Draw the equivalent circuit of a 3-phase induction motor.
22. Why do we say that Induction motor is similar to a rotating transformer?
23. What are the parameters required to draw a circle diagram?
24. Draw the performance curves of an induction motor.
25. What is the advantage of a circle diagram?
26. Why iron losses are considered-as zero?
27. What is relation between Torque, power and angular velocity?
28. Define speed regulation.
29. Does speed falls from no load to full load. if so, how much?
30. Why rotor bars in a squirrel cage rotor are skewed?
31. If the external resistance is kept permanently in the rotor circuit, what is the disadvantage?
32. What are the different power stages in an induction motor?
33. What is the electrical equivalent of mechanical load in an induction motor?
34. Which types of instruments are used in A.C. circuits and D.C. circuits and both?
35. Which instruments are called Transfer instruments?
36. What are the different types of analogue instruments?
37. Write Torque equation for induction motor.
38. Explain circle diagram
39. What is Cogging and Crawling in an induction motor? How are they prevented?
40. What is the speed of an induction motor for (i) 4% Slip (ii) 100% slip?
Synchronous Machines:
29. Explain why synchronous machines are designed to have a high ratio of armature reactance
to resistance?
30. Why alternators run in parallel?
31. Draw the phasor diagram for alternator and synchronous motor for leading and lagging
power factors.
32. What is the role of damper windings?
33. ln which type of alternator, damping windings does not exist?
34. When do we say an alternator is under floating condition during parallel operation?
35. Which machine requires both AC and DC?
36. Equation for emf generated in a synchronous motor.
37. What is pitch factor and distribution factor?
38. What is meant by full pitch winding?
39. Draw the curves between V and l. at distribution power factor loads.
40. What is short circuit ratio?
41. Potier triangle is drawn between which two characteristics?
42. Which method is used to find out the regulation in a salient pole Synchronous machine?
43. Define Xq and Xd .
44. Draw the graph between torque angle and Po for a Synchronous machine.
45. What are the different methods used for parallel operation of the alternator?
46. How do you increase the voltage of an alternator?
47. Draw the graph of V and inverted V curves for different loads.
48. When do you say the synchronous motor is running as a reluctance motor?
1. Which theory explains the performance of the single phase induction motors?
2. What are the different types of single-phase motors?
3. Draw the phasor diagram for sprit-phase and capacitor-run motors.
4. Explain Cross field theory.
5. Explain' Double revolving field theory.
6. What is the importance of the compensation in single phase motors?
7. What are the applications of Universal motors?
8. What are the applications of Shaded pole motor?
9. Explain the importance of capacitors in capacitor start motors.
10. Why the single phase motors are not self starting?
11. When a single phase series motor is operated on no-load.
12. What are the motors used for household refrigerators, ceiling fans, hair dryers and mixes.
13. When a capacitor start single phase induction motor is switched on the supply with its
capacitor replaced by an inductor of equivalent reactance value. What will happen?
14. Lf the ceiling fan when switched on, runs at slow speed in the reverse direction what is your
conclusion?
15. How can you reverse the speed of the split phase motors?
16. How will the reluctance motor run?
17. How will the repulsion motor run?
18. How will the hysteresis motor run?
19. What are the differences between AC series motors & DC series motors?