Question Bank
Unit-1
Q1. Using loop current method, find the current I1 & I2 shown in fig.
[UPTU, II SEM, 2005-06]
Q2. Find the current in, and voltage across the 2ohm resistance in fig.
[UPTU, I SEM, 2008-09]
Q3. Using Nodal Analysis, find Vcd for the circuit shown in fig.
[ UPTU, Sem I, 2007-08]
Q4. Use Nodal Analysis to find the current in various resistors of the circuit shown in fig.
[ UPTU, Sem II, 2005-06]
Q5. Find the currents in all the resistive branches of the circuit shown in fig:
(i)
(ii)
KVL
KCL
[ UPTU, II Sem, 2007-08]
Q6. Replace the network of the circuit in fig. to the left of the terminals ab by its Thevenin’s equivalent
circuit. Hence determine I.
[ UPTU, II Sem, 2008-09]
Q7. Using Thevenin theorem obtain current in 13ohm resistance in fig:
[ UPTU, II Sem, 2008-09]
Q8. Determine the current following through the 5 ohm resistor in the network of fig: by using Thevenin
Theorem.
[ UPTU, Sem II, 2002-03]
Q9. The resistance of various arms of a bridge are given as in fig. The battery has an emf of 2.0V and
negligible internal resistance. Determine the value and direction of current in BD using Thevenin Theorem
only.
[UPTU, Caryover, 2005-06]
Q10. Using Thevenin equivalent circuit across AB shown in fig:
[ UPTU, II Sem, 2005-06]
Q11. Determine the value of current through the 5 ohm resistor using nortons theorem in the circuit shown
in figstate whether super position can be applied for the circuit with reason.
[ UPTU, II Sem, 2007-08]
Q12. Find the Norton’s equivalent circuit as seen by RL in the circuit in fig:
[ UPTU, Sem I, 2007-08]
Q13. Find the current flowing through the 12 ohm resistor in the circuit of fig: using Norton’s Theorem,
[ UPTU,II Sem, 2003-04]
Q14. Explain maximum power transfer theorem. Using this theorem, find the value of the load resistance RL
for maximum power flow through in fig:
[ UPTU, Sem II, 2006-07]
Q15. In the network in fig:, find,
(i)
(ii)
The value of RL, for maximum power dissipation
The value of maximum power
[ UPTU, Sem II, 2007-08]
Q16. Find the resistance between AB of the circuit.
[ UPTU, II Sem, 2005-06]
Q17. In the circuit of fig: find the current thje 6 ohm resistor using Super Position Theorem.
[UPTU, Sem II, 2007-08]
Q18. Find the current I in the circuit of fig: using Mesh Analysis:
[ UPTU, Sem II, 2006-07]
Q19. Determine the current ix & iy in the network of fig: State Theorem used.
[ UPTU, Sem I, 2008-09]
Q20. In the circuit shown in fig: find the current through 6 ohm resistor by using Nodal Analysis.
[ UPTU, Sem II, 2007-08]
Q21. Find the current I in the circuit shown in fig: using Nodal Analysis.
[ UPTU, Sem II,2006-07]
Q22. Find Current I in the circuit shown in fig: using Thevenin Theorems.
[UPTU, Sem II, 2006-07]
Unit-2
Based on AC fundamental:-
T-1 Find average, RMS, Form factor and Peak factor of given waveform: [Refn UPTU-2004-05 II Sem]

[Ans:-5,5.7735,1.154,1.73]
T-2 Find average, RMS, Form factor and Peak factor of given waveform: [Refn UPTU-2003-04 II sem]
[Ans:- 31.83,50, 1.57,2]
T-3 Find average, RMS, Form factor and Peak factor of given waveform:
[Refn NPTL ]
[Ans:- 3.75,4.08,1.088,1.22]
Based on R-L-C :-
T-4
An R-L-C series ckt consist of a resistance of 1000 ohm , an inductance of 100 mH and a capacitance
of 10 Micro farad.Determined:[Refn UPTU:-2000-01 I sem]
(a) Resonance frequency
(b) Q-factor
(c) Half power frequency.
[Ans:- 159.2 Hz,0.1,1607.31Hz]
T-5 A coil having a resistance of 6 ohm and an Inductance of 0.0255 H is connected across a 230 V,50Hz
AC supply. Calculate:(a)
(b)
(c)
(d)
[Refn MTU:-2009-10 I sem]
Current
Power factor
Active power
Reactive power
[Ans:- 23<-36.87,0.8 lagging ,4232W,3174VAR]
T-6
Draw a vector diagram for the circuit shown indicating the terminal voltage V1 and V2 and the
current. Find the values of (a) the current (b) V1 and V2 (c) the power factor.
[Refn UPTU:-2006-07 II sem]
[Ans. (a) 5.84A; (b) 108.2V, 221.5V; (c) 0.875 leading]
T-7
An inductive coil is connected to a supply of 250 Volt at 50 Hz and takes a current of 5Amp. The coil
dissipates 750W. calculate the resistance and inductance of the coil and power factor of the coil.
[Refn UPTU carry over:-2005-06]
[Ans. 30 Ohm,0.127 H,0.6 leading]
T-8
A 120 V , 100W lamp is to be connected to a 220 V, 50HZ a.c. supply. What value of pure inductance
should be connected in series in order that lamp is run on rated voltage.
[Refn UPTU 2003-04 I Sem]
[Ans. (i) 99W, .92 leading (ii) 195  ]
T-9
A resistor and a capacitor are connected in series across a 150V ac supply. When the frequency is
40Hz, the circuit draws 5A. When the frequency is increased to 50Hz, it draws 6A. Find the values of
resistance and capacitance. Also find the power drawn in the second case.
[Refn UPTU 2004-05 II sem]
[Ans. 11.662  , 144µF, 420W]
T-10
Two impedance Z1 and Z2 when connected separately across a 230-V, 50Hz supply consumed 100W
and 60W at power factors of 0.5 lagging and 0.6 leading respectively. If these impedances are now
connected in series across the same supply, find:
(i)
T-11
total power absorbed and overall p.f. (ii) the value of the impedance to be added in series so
as to raise the overall p.f. to unity.
[Ans. (i) 99W, .92 leading (ii) 195  ]
A resistor of 12  and an inductance of 0.025H are connected in series across a 50Hz supply. What
values of resistance and inductance when connected in parallel will have the same resultant
impedance and p.f. Find the current in each case when the supply voltage is 230V.
[ Ans. 17.14  , 83.2mH, 16.04 33.2 A]
T-12
Find the value of R and C so that Vb = 3Va and Vb and Va are in quadrature. Find also the phase
relation between V and Vb; Va and I.
Ans. R = 2.66  ; C = 1590µF
Va lags behind the current by 37°
Vb leads the current by 53°
Vb leads V by 18.3°
T-13
A 480V source energizes two loads in parallel supplying 2KVA at a 0.5 lagging power factor to one
load and 4 KVA at a 0.6 leading power factor to the other load. Find the source current and also the
total impedance of the combination.
Ans. I = 7.72 23.5 A , Z = 62.17 23.5
T-14
Two impedances Z1 = (8+j6) and Z2 = (3-j4)  are in parallel. If the total current of this combination is
25A, find the power taken by each Impedance and voltage across them.
Ans. PZ1 = 1KW , PZ 2 = 1.5KW, 111.8 26.57 V
Short Question
T-15
What is resonance in parallel circuit? Explain.
[Refn UPTU 2003-04 II sem]
T-16
Derived an expression for the instantaneous current drawn y a pure inductive circuit on application of
a sinusoidal voltage and show that current lags behind voltage by a quarter cycle.
[Refn UPTU 2004-05 I sem]
T-17 Explain the selectivity of RLC resonance circuit. Prove that it reciprocal of quality of the circuit..
[Refn UPTU 2004-05 II sem]
T-18
Show that the average power demand ,in a purely inductive A.C. circuit is Zero.
[Refn UPTU 2003-04 I sem]
T-19
Explain the concept of band width and quality factor in series R-L-C circuit. Derive an expression.
[Refn UPTU 2007-08 I sem]
T-20
What are active and reactive powers? Why is the term ‘reactive power’ not encountered when d-c
source are used in an electric circuit?
[Refn UPTU 2008-09 II sem]
Unit 3
Q.1 In 2-Wattmeter method, power measured was 30KW at 0.7 p.f. lagging.Find reading
Of each Wattmeter.
[MTU 2011-12]
Q.2 A 400v 3 phase source supplied power to both delta and star connected laods
connected in Parallel. All the phase impedances are identical and equal to (5+j8.66)
ohms. Calculate total Line current and power drawn from source.
[MTU 2011-12]
Q.3 Derive the relation between line voltage and phase voltage in3 phase star ckt. Also
derive the Expression for power.
[MTU 2010-11]
Q.4 Derive expression for power in 3phase Y & delta. A balanced Y connected load of
(8+6j) ohm/phase is connected to A balance 3 phase, 400 v supply. Find the line
Current, pf &power.
Q.5 A balanced 3-phase star connected load of 150kW takes a leading current
100A with a line voltage of 1100V, 50Hz. Find the circuit constants of the load per
phase.
[Ans. R = 5  XC= 3.9  , C = 816µF]
Q.6 A 3 wire 3 phase supply feeds a load consisting of three equal resistors. By how
much is the load reduced if one of the resistors be removed (a) when the load is
star connected (b) when the load is delta connected?
[Ans. (a) 50%, (b) 33.3%]
Q. 7
A 3-phase star-connected alternator feeds a 2000 hp delta-connected induction
motor having a P.F. of 0.85 and an efficiency of 0.93. Calculate the current and the
active and reactive components in (a) each alternator phase (b) each motor phase.
The line voltage is 2200V.
[Ans. (a) 495A, 421A, 261A (b) 286A, 243A, 151ª]
Q.8 A delta connected load draws a current of 15A at lagging P.F. of .85 from 400V,
3-phase, 50Hz supply. Find R & L of each phase.
[ Ans. 42.98  , 53.7mH.]
Q.9
A balanced 3-phase star connected load of 100 KW takes leading current of 80A,
when connected across 3-phase, 1100V, 50Hz supply. Find component of load per
phase.
[Ans. R = 5.2  , C = 532µF]
Q.10 Three 100  non-inductive resistance are connected in (a) star (b) delta across a
400-V, 50Hz, 3-phase mains. Calculate the power taken from the supply system in
each case
[Ans. 1600W, 4800W]
Q.11 Each phase of star connected load consists of non-inductive resistance of 50  in
parallel with a capacitance of 63.6µF. Calculate the line current, total power
absorbed, total kVA and the power factor when this load is connected to a 381 V
(line voltage), 3-phase, 50Hz supply.
[Ans.6.22A, 2.9kW, 4.1kVA, .707]
Q.12 A 3-phase, 37.3kW, 440-V, 50Hz induction motor operates on full load with an
efficiency of 89% and at a power factor of 0.85 lagging. Calculate the total KVA
rating of capacitors required to raise the full-load power factor at 0.95 lagging. What
will be the capacitance per phase if the capacitors are (a) delta-connected and (b)
star-connected?
[Ans. 65.79µF, 197.4µF]
Q.13 A symmetrical 3-phase, 3-wire supply with a line voltage of 173 V supplies two
balanced 3-phase laods; one Y-connected with each branch impedance equal to
(6+j8) ohm and the other
-connected with each branch impedance equal to
(18+j24) ohm. Calculate
(i) The magnitudes of branch current taken by each 3-phase load
(ii) the magnitude of the total line current and
(iii) the power factor of the entire load circuit
Draw the phasor diagram of the voltages and currents for the two loads.
[Ans. (i) 10A (ii) 20A (iii) 0.6 lag]
Q.14 Three identical impedance of 30 30 ohms are connected in delta to a 3-phase, 3wire, 208 V abc system by conductors which have impedances of (0.8+j0.63) ohm.
Find The magnitude of the line voltage at the load end.
[Ans. 109.00 V]
Q.15 A balanced delta-connected load having an impedance ZL= (300+j210) ohm in
each phase is supplied from 400V, 3-phase supply through a 3-phase line having an
impedance of Zs = (4+j8) ohm in each phase. Find the total power supplied to the
load as well as the current and voltage in each phase of the load.
[Ans. 1158.2W, 1.78A, 216.9V]
Q. 16
Two wattmeters are used for measuring the power input and the power factor of
an over-excited synchronous motor. If the reading of the meters are (–2.0kW) and
(+7.0 kW) respectively, calculate the input and power factor of the motor.
[Ans. 5kW, .305]
Q.17
The two wattmeters A and B, give readings as 5000W and 1000W respectively
during the power measurement of 3-phase, 3-wire, balanced load system.
Calculate the power and power factor if (i) both meters read direct and (ii) one of
them reads in reverse, (b) If the voltage of the circuit is 400V, The frequency of
supply is 50Hz.
[Ans. (i) 6000 W , .655 (lag) (ii) 4000W , .36 (lag)]
Q. 18
A direct current ammeter and leads have a total resistance of 1.5  . The
instrument gives a full-scale deflection for a current of 50mA. Calculate the
resistance of the shunts necessary to give full-scale ranges of 2-5, 5.0 and 25.0
amperes.
Q. 19
[Ans. 0.0306  ; 0.01515  ; 0.00301  ]
A single phase energy meter makes 500 revolutions per kWh. It is found on
testing as making 40 revolutions in 58.1 seconds at full load of 5kW. Determine
the percentage error.
[Ans. –.860% slow]
Q.20
A moving coil instrument has a resistance of 75  and gives a full-scale
deflection of 100 scale divisions for a current of 1mA. The instrument is
connected in parallel with a shunt of resistance 25  & the combination is then
connected in series with a load and a supply. What is the current in the load when
the instrument gives an indication of 80 scale divisions?
[Ans. 3.2mA]
Q.21 A moving coil voltmeter has a resistance of 100  . The scale is divided into 150
equal divisions. When a potential difference of 1V is applied to the terminals of
the voltmeter a deflection of 100 divisions is obtained. Explain how the instrument
could be used for measuring up to 300V. Give a diagram of connection. Determine
the value of component used.
[Ans. 19.9k  ]
Q. 22 While determining the resistance R of a conductor, a student by mistake connects
ammeter in parallel with R and voltmeter in series as shown. What are the
readings of ammeter and voltmeter? The resistance of the voltmeter is 2000 
and the resistance of the ammeter is negligible.
[Ans. 1mA, 2V]
Q. 23 Two voltmeters, one with a full-scale reading of 100V and another with a fullscale reading of 200V, are connected in series across a 100 V supply. The
internal resistance of both meters is the same. What will be the readings of the
voltmeters?
[Ans. 50V, 50V]
Unit-4
Q-1.
Define the following terms as applied to magnetic circuits:
(i)M.m.f. (ii) flux density (iii)reluctance (iv) permeability (v) relative
permeability.
UPTU II SEM Exam. (2002-2003)
Q-2. A coil of 1000 turns is wound on a laminated core of steel having a cross-section of 5 cm2. The
core has an airgap of 2mm cut at right angle. What value of current is required to have an air gap
density of 0.5 T. Permeability of steel may be taken as infinity. Determine the coil inductance
(Ans: 0-314 H)
UPTU I SEM Exam, (2003-2004)
Qu.3 Differentiate between electric and magnetic circuits. Also give relation between mmf flux and
reluctance.
UPTU II SEM Exam, (2003-2004) ,I SEM Exam, (2004-2005)
Qu.4 Two coils having 100 and 50 turns respectively are wound on a core with µ= 4000µo Effective core
lenth =60 cm and core area =9 cm2 . Find the mutual inductance between the coils. Ans=0.03769H
UPTU II SEM Exam, (2004-2005)
Qu.5 An iron ring of 60cm mean circumference has a cross sectional area of 8cm2 and there is an air gap
of 5mm width cut in the ring. The ring is wound with a coil of 1000 carrying a current of 2.5A. Find the
flux in the air gap. The relative permeability of iron is 750.
Ans.
0.4338mWb
UPTU II SEM Exam, (2004-2005)
Qu 6 Explain relative permeability. Calculate the mmf required to produce a flux of 0.015 Wb across an
airgap 2.5 mm long having an effective area of 200 cm2.
Ans 1492AT
UPTU Carry overExam, (2005-2006)
Qu,7 The core of a magnetic circuit is of mean length 40 cm and uniform cross-sectional area 4cm2 . The
relative permeability of the core material is 1000 turns are wound on the core. Determine the
inductance of the coil if fringing is negligible.
Ans:
UPTU (I SEM Exam, (2008-2009)
Qu. 8 A circular ring of mean diameter 20cm and cross-sectional area 12.5cm2 is made up of two
semicircular sections of cast iron and cast steel, with each joint having a reluctance equal to air gap
of 0.3mm. Find ampere-turns needed to produce a flux of 10-3 Wb. Relative permeabilities of cast
steel and cast iron are 700 and 160 respectively. Neglect fringing and leakage effects.
Ans. 1916
Qu 9 A 3300V/200V, 50Hz, 100KVA transformer has its low voltage winding with 80 turns.
Calculate
(i) The currents in both windings.
(ii) Number of turns of high voltage windings and
(iii) Maximum value of the flux. Given that the transformer is loaded to it full capacity.
Ans. (i) 30.303A, 500A (ii) 1320 (iii) 11.26mWb
UPTU I SEM Exam, (2003-2004)
Qu 10. A 1  6600/600V transformer has a load impedance of (4+j3)  connected across the
terminals of low voltage winding. Calculate the KW delivered to the load. Neglecting losses,
find the current taken by it from the supply line.
Ans.
57.6KW, 10.9A
Qu. 11. Draw the phasor diagram of a single phase transformer for leading power factor load.
UPTU SEM-II 2007-2008
Qu.12 .Explain basic principle of transformer.Where are they used?
Qu.13. Explain with a phasor diagram the function of the no load current of a static transformer.
Qu.14. List various types of losses occurring in a transformer.How does each loss vary when (a) only
the voltage varies (b) only frequency varies (c) load varies at constant voltage and
frequency?
Qu.15. A 2200/220, 44KVA transformer has 50 turns in the secondary. Assuming the losses to be
negligible, calculate (i) primary turns (ii) Primary & secondary full load currents.
Ans. (i) 500 (ii) 200A
Q.16. A single phase 50Hz core type transformer has cross section area of 400cm2. The permissible
maximum flux density is 1Wb/m2. Calculate the number of turns per limb on the high & low
voltage sides for a 3000/220 ratio.
Ans. 169, 13
Q. 17. A 100  source is to be matched to a 40  , 2Watts load by means of a transformer. What is
the turns ratio? Determine the primary & secondary voltages and currents.
Ans. 1:1.58, 8.94V, 14.13V, 0.2236A, 0.1414A
Qu.18. A 200KVA, 3300/240V, 50Hz single phase transformer has 80 turns on secondary winding.
Calculate:
(i) Primary and secondary currents on full load.
(ii) Maximum value of flux.
(iii) Number of Primary winding turns.
Ans. 60.6 A, 833.33 A, 13.51mWb, 1100
Q. 19. A 400V/100V transformer takes no load current of 5A at 0.2 lagging p.f. Secondary winding
supplies a load 100A at a p.f. of 0.8 lagging. Find the primary input current.
Ans. 28.93 A
Q.20. Discuss the voltage structure of the of the electric power system. Give the con cept of the
grid.
Qu.21. List out main components of power supply system with a brief description. Also write the
advantages of power factor improvement.
Qu.22. Draw the general layout of an electrical power system and explain briefly.
Qu.23. Explain clearly the difference between feeder distributer & service mains.
Qu.24. Explain 3-phase -4 wire system of distribution of electric power.
Qu.25. Give reasons why is power transmitted by 3-phase, 3 wire system where as the distribution is
done by 3-phase, 4 wire system.
UPTU I SEM Exam, (2003-2004)
UPTU I SEM Exam, (2003-2004)
Unit-5
Q. 1.
A 8 pole lap wound DC generator has 70 slots in its armature with 22 conductors per slot. The ratio
of pole are to pole pitch is 0.64. The diameter of the bore of the pole shoe is 0.48m. The length of
the pole shoe is 0.28m. The air gap flux density is 0.32Wb/m 2 & the generated emf in the armature
is 400V. Find the speed of generator.
Ans. 1442
Q. 2.
A 6-pole DC shunt generator has the following data Field resistance = 120  , armature resistance =
0.8  Number of conductors = 350 (Wave connected) Flux per pole= 0.02Wb Load resistance across
the terminals = 12  , armature rotates at 1000 rpm. Calculate power absorbed by load
Ans. 8859.6W
Q. 3
A 220V DC series motor has an armature resistance of 0.3  and field resistance of 0.2  . It runs at
a speed of 700 rpm taking a current of 15A. Calculate the resistance to be inserted in series with
the armature to reduce the speed to 600rpm. The input current remains constant. Assume that the
magnetization characteristics is st. line.
Ans. 2.02 
Q. 4.
A 250V, DC shunt motor on no-load, runs at a speed of 1000 rpm and takes a current of 5A the
armature and shunt field resistances are 0.2  and 250  respectively. Calculate the speed when
the motor is on-load, and is taking current of 50A. Assume that the armature reaction weakens the
field by 3%.
Ans. 993.7rpm
Q. 5.
Determine developed torque and shaft torque of 220V, 4-pole series motor with 800 conductors
wave connected & supplying a load of 8.2KW by taking 45A from the mains. The flux per pole is
25mWb and its armature circuit resistance is 0.6  .
Ans. 286.2N-m 270.5N-m
Q. 6
A 140 v DC shunt motor has an armature resistance of .2 ohm &field resistance 70 ohm . The full
load current is 40A & full load speed is 1800rpm . If brush drop is 3 v, find speed of motor at half
load.(2009-10)
Ans 1855.61rpm
Q. 7
A lap-connected 8-pole generator has 500 armature conductors and useful flux of 0.07Wb.
Determine the induced emf when it runs at 1000rpm. What must be the speed at which it is to be
driven to produce the same emf if it is wave wound?
Ans.
583.3V,
250rpm
Q.8.
Determine the power output of a dc motor armature having 1152 lap-connected conductors
carrying 150A and rotating at 300rpm in a 12-pole. The flux/pole is 60mWb.
Ans. 51.84KW
Q. 9.
A dc shunt generator has an armature resistance of 0.25  and the resistance of shunt
field is 220  . While delivering a load current of 50A, it has terminal voltage of 440V. Determine
the generated emf.
Ans.
453V
Q. 10. A shunt Generator has an induced voltage on open circuit of 127V. When the machine is loaded,
terminal voltage is 120V. Find the load current if the field resistance is 15  and armature
resistance is 0.02  . Ignore armature reaction.
Ans. 342A
Q. 11. A d.c. shunt generator is supplying load connected bus bar voltage of 220V. It has an armature
resistance of 0.025  and field resistance of 110  . Calculate the value of load current and load
power when it generates an emf of 230V.
Ans. 398A, 87.56KW
Q. 12. A 230V d.c. shunt Motor takes 51A at full load. Resistance of armature and field windings are
0.1  and 230  . Determine (i) field current (ii) armature current
(iii) back emf developed at full load
Ans. (i) 1A (ii) 50A (iii) 225V
Q. 13. A 250V d.c. shunt Machine has line current of 80A. It has armature & field resistance of 0.1  and
125  respectively. Calculate Power developed in armature when running as (a) Generator (b)
Motor.
Ans. (a) 21.172KW (b) 1889KW
Q. 14. A 230V dc shunt Motor runs at 800rpm and takes armature current of 50A. Find the resistance to
be added to the field circuit to increase speed to 1000 rpm at an armature current of 80A. Assume
armature resistance 0.15  and field winding resistance = 250 
Ans. 68.95 
Q. 15. A 200V dc shunt Motor has Ra=0.2  and Rsh=200. If the no load and full load current drawn by
the motor are 5A and 40A respectively. Calculate the full load speed, assuming that no load speed
is 1000 rpm.
Ans. 964.85rpm
=
Q. 16. A 10KW , 200V, 1200 rpm series DC Generator has armature resistance of 0.1  , field winding
resistance of 0.3  . The frictional & winding loss of the machine is 200W and brush contact drop is
1V per brush. Find the efficiency of the machine and the load current, at which this machine has
maximum efficiency.
Ans. 88.49%, 50A
Q. 17. A 3-phase, 400V, induction motor is wound for 4 poles and is supplied from 50Hz supply system.
Calculate (i) synchronous speed (ii) the speed of the motor when slip is 4%.
Ans. (i) 1500 rpm, (ii) 1440
rpm
18.
A 6 pole 3-phase alternator is coupled to an engine running at 1000rpm. It is supplied by 3-phase
induction motor having full load speed 1480 rpm. Find the no. of poles of motor, %slip, frequency of rotor
current.
Ans. 4, 1.3%, 0.65Hz
Q. 19. 3-phase, 6 pole, 50Hz star connected induction motor delivers useful power 25kW white running at
a speed of 950rpm. It is connected to a supply of 400V takes current of 60A. Its stator resistance
per phase is 0.14  . Mechanical losses are 900W Calculate (i) shaft torque (ii) gross torque (iii)
rotor copper loss (iv) stator copper loss.
Ans. (i) 251.4N-m (ii) 260.47N-m (iii) 1363.1W (iv) 1512W
Q. 20. Rotor of a 4 pole 3-phase induction motor operates from a supply whose frequency is 50Hz.
Calculate (i) Speed at which magnetic field is rotating w.r.t. stator, (ii) Speed of rotor when the slip
is 0.04, (iii) Frequency of rotor currents at stand still.
Ans. (i) 1500rpm (ii) 1440rpm (iii) 50Hz