DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
G.H.RAISONI COLLEGE OF ENGINEERING
DEPARTMENT OF ELECTRICAL ENGINEERING
BASIC ELECTRICAL ENGINEERING QUESTION BANK
A.C. CIRCUITS
SUMMER – 2001
Q.1. Three inductive coils, each with a resistance of 15 ohms and an inductance (6m)
of 0.03 H are connected (i) in star and (ii) in delta, to a 3-phase 400 V, 50 Hz. Supply.
Calculate for each of the above case
(i)
phase current and line current and
(ii)
total power absorbed.
Q.2. A circuit having a resistance of 5 ohms, an inductance of 0.4 H and a
(7m)
variable capacitance in series, is connected across a 110 V, 50 Hz. Supply. Calculate:
(i)
The value of capacitance to give resonance
(ii)
Current
(iii) Voltage across the inductance
(iv)
Voltage across the capacitance
(v)
Q-factor of the circuit.
Q.3. Draw the phasor diagram for each of the following combinations.
(6m)
(i)
R and L in series and combination in parallel with C
(ii)
R and C inseries and the combination in parallel with L
(iii) R, L and C in series, with XL>XC, when ac source is connected to it.
Q.4. a sinusoidal 50c/s current of maximum value of 100 A flows through a
capacitor of 318 µF capacitane. Calculate:
(i)
the expression for instantaneous current,
(ii)
reactance of capacitor
(iii) equation of applied e.m.f.,
(iv)
r.m.s. value of applied e.m.f. and current.
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(7m)
DEPARTMENT OF ELECTRICAL ENGINEERING
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WINTER– 2001
Q.1. A varying current, with a periodic waveform as shown in figure flows
through an 8 ohms resistor. Determine
(i)
the mean value
(ii)
the rms value
(iii) the heat dissipated in 5 minutes
(6m)
i
6A
0.06
0.10
0.04
t,sec.
-2A
Q.2. Fig. shows the phasor of currents flowing through the three different circuits:
(i)
State the type of elements of its combination in the respective circuit.
(ii)
If all the three circuits are connected in parallel, calculate the total current
with its phase angle.
(iii) Draw the waveforms of all four current.
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
V
A
I2=4A
30
I1=5A
I1=3A
Q.3. An inductive coil having resistance of 20 ohms and inductance of 0.1 H is connected
in series with 10 µF capacitor. The combined circuit is energized from 200 V, variable
frequency supply.
Calculate:
(i)
the phase and line quantities of voltage and current.
(ii)
1-Φ and 3-Φ active and reactive power consumed by the load.
(iii) Draw the phasor diagram including all quantities.
SUMMER – 2002
Q.1. Define r.m.s. and average value as applied to ac voltage, prove that in (6m)
pure inductive circuit, current lags behind applied voltage at an angle 900.
(Down waveform).
Q.2. A series RLC circuit consists of
R =10 Ω
L = 0.318 H
C=63.6 µF and
emf source e(t) = 100 sin 314 t, calculate :
(i)
Expression for i(t)
(ii)
Phase angle between voltage and current
(iii) Power factor.
(iv)
Active power consumed,
(v)
Draw the phasor diagram.
(8m)
Q.3. Show that the power consumed by three identical phase loads connected (6m)
in delta equal to three times the power consumed when the phase loads are connected in
star.
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Q.4. A delta-connected load draws a current of 15 A at a lagging power factor of
0.85 at a 400 V, 3-Φ, 50 Hz supply. Calculate:
(i)
Resistance and inductance of each phase,
(ii)
Power consumed.
(7m)
WINTER– 2002
Q.1. The equation of voltage and currents in two element series circuit are:
v(t) = 325.3 sin(6.28 kt + П/3) volts
i(t) = 14.142 sin(6.28 kt + П/3) amp.
(i)
(ii)
(iii)
(6m)
plot the power p(t) on wave diagram.
Determine power factor and its nature.
Determine the elements value.
Q.2. A pure capacitor is connected in series with practical inductor coil.
(7m)
The voltage source is of 10 volts, 10,000 Hz. It was observed that the maximum current
of 2 amp. flows through the circuit when the value of capacitor is 1 µF. Find the
parameter (R and L) of the coil.
Q.3. Prove that the power consumed in balanced three-phase delta connected load (6m)
is three times the power consumed in star-connected load.
Q.4. A three-phase 230 volts systems supplies a total load of 2000 watts at a line current
of 6 amp when three identical impedance are in star-connection across the line terminals
of the system. Determine the resistive and reactive components of each impedance.
SUMMER – 2003
Q.1. A circuit takes a current of 8 A at 100 V, the current lagging by 300 (7m)
behind the applied voltage. Calculate the values of equivalent resistance and
reactance of the circuit.
Q.2. Draw the phasor diagram for each of the following combinations.
(6m)
(iv)
R and L in series and combination in parallel with C
(v)
R and C inseries and the combination in parallel with L
(vi)
R, L and C in series, with XL>XC, when ac source is connected to it.
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Q.3. Derive the relationship between phase voltage and line voltage in case (6m)
of balanced star connected load.
Q.4. Three similar coils each of impedance z=(8+j10) ohms, are connected (8m)
in star and supplied from 3-phase 400 V, 50 Hz supply. Find the line current, power
factor, power and total volt-amperes.
WINTER– 2003
Q.1. Find the rms value, average value, form factor and peak factor for the
waveform shown in figure.
(5m)
i(t)
Im
T/2
3T/20
T
7T/20
Im
Q.2. A current of 5 A flows through a non-inductive resistance connected in series (8m)
with a choke coil when supplied at 250 V, 50 Hz. If voltage across resistance is 125 V
and across coil is 200 V. Calculate:
(i)
impedance, resistance and reactance of coil
(ii)
power in coil
(iii) total power consumed in the circuit
(iv)
draw phasor diagram
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Q.3. Two impedances Z1=(6+j8) ohm and Z2=(8-j6) ohm are connected in parallel (6m)
across 100 V supply. Determine:
(i)
current and power factor of each branch
(ii)
overall current and power factor
(iii) power consumed by each branch and total power
Q.4. Three similar coils each having a resistance of 20 ohm and an inductance
(7m)
of 0.05 H are connected in star to a 3-phase 50 Hz supply with 400 V between line.
Calculate power factor, total power absorbed and line current.
If the same coils are reconnected in delta across the same supply what will be the
power factor, total power absorbed and line current?
SUMMER – 2004
Q.1. The current in each branch of a two branched parallel circuit is given as :
ia = 7.07 sin(314t – П/4); ib= 21.2 sin(314t + П/3)
and supply voltage is V = 354 sin 314t
Calculate:
(i)
total current in the same form
(ii)
calculate the ohmic value of components in each branch
(7m)
Q.2. Two choke coils are connected in series as shown below:
Internal resistance and its inductive resistance of coil A is 4 and 8
(7m)
respectively. Supply voltage is 200 V. Total power consumed in the cicuit is 2.2 KW and
reactive power consumed is 1.5 KVAR. Find the internal resistance and inductive
reactance of coil B.
Coil A
Coil B
Q.3. A 3φ star connected load when supplied from 440 V, 50 Hz source takes
a line current odf 12 amp lagging w.r.t. voltage by 700.
Calculate:
(i)
impedance parameters
(ii)
power factor and its nature
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DEPARTMENT OF ELECTRICAL ENGINEERING
(iii)
(iv)
FIRST YEAR ELECTRICAL ENGINEERING
total power consumed
draw phasor diagram indicating all voltages and currents.
Q.4. Derive the relationship between line current and phase current for delta
connected phase load when supplied from 3-phase balanced supply.
(5m)
WINTER– 2004
Q.1. Define and explain the following terms as applied to A.C. circuit :
(i)
frequency
(ii)
power factor
(iii) impedance
(6m)
Q.2. For the series circuit shown in figure and with the current and voltages
(7m)
as indicated, Calculate the values of R, r and L and the frequency of the applied voltage
and its magnitude.
35A
r
R
25A
L
50µF
40V
50v
V
Q.3. A balnced star-connected load is supplied from a symmetrical three phases, (6m)
400 V (line-to-line) supply. The current in each phase is 50 A and lags 300 behind the
phase voltage. Find:
(i)
phase impedance
(ii)
active and reactive power drawn by load
(iii) draw phasor diagram showing phase and line voltages and line current.
Q.4. Two impedances (14+j5)ohms and (18+j10)ohms are connected in parallel
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(7m)
DEPARTMENT OF ELECTRICAL ENGINEERING
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across a 220 V, 50 Hz supply. Determine:
(i)
impedance of the entire circuit
(ii)
total current, power and power factor
(iii) draw the phasor diagram for above circuit indicating all the electrical
quantities.
SUMMER – 2005
Q.1. . Draw the phasor diagram for each of the following combinations.
(6m)
(vii) R and L in series and combination in parallel with C
(viii) R and C inseries and the combination in parallel with L
(ix)
R, L and C in series, with XL>XC, when ac source is connected to it.
Q.2. Two impedances Z1 and Z2 when connected separately across a 230 V,
(7m)
50-Hz supply consume 100 watt and 60 watt at a 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)
total power absorbed and overall power factor
(ii)
the value of of the impedance to be added in series so as to raise the
overall power factor to unity.
Q.3. Derive the relationship between line current and phase current for delta
connected load.
(7m)
Q.4. A delta connected load draws a current of 20 a at a lagging power factor of 0.8 from
a 400V, 3 phase, 50 Hz supply. Calculate:
(i)
Resistance and inductance of each phase.
(ii)
Power consumed.
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DEPARTMENT OF ELECTRICAL ENGINEERING
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WINTER– 2005
Q.1. What is the significance of rms value and average value of a wave?
(7m)
Determine rms and average value of the waveform as shown in figure below.
Y
20
10
2T
T
time
Q.2. A 20 Ω resistor is connected in series with an inductor, a capacitor and an
(6m)
ammeter across 25 V variable frequency supply. When the frequency is 400 Hz, the
current is at its maximum value of 0.5 A and potential difference across capacitor is 150
V.
Calculate:
(i)
capacitance of the capacitor
(ii)
resistance and inductance of the inductor.
Q.3. A coil of inductance 80 mH and resistance 120Ω is connected to a 230 V, (9m)
50 Hz, single-phase supply. In parallel with it is a series combination of 16 µF capacitor
and a 40 Ω non-inductive resistor B. Determine the power factor of combined circuit, the
total power taken from the supply and current through each branch.
Q.4. Three identical impedances are connected in delta to a 3-Φ supply of 400 V.
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DEPARTMENT OF ELECTRICAL ENGINEERING
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The line current is 35 A and total power taken from supply is 15 KW. Calculate the
resistance and reactance of each impedance.
SUMMER – 2006
Q.1. Find the rms value, average value and form factor for the waveform shown in figure:
20
10
0
T
2T
3T
Q.2. For the circuit shown below, find:
(i)
total current
(ii)
pf of the circuit
(iii) total power taken from the source
(iv)
energy stored in inductor and capacitor
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(7m)
DEPARTMENT OF ELECTRICAL ENGINEERING
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0.5H
90ohms
20µF
230V,50 Hz
Q.3. Prove that the power consumed in balanced 3-phase delta connected load is
3-times the power consumed in star connected load.
(5m)
Q.4. A 3-phase load consists of 3 similar inductive coils, each of resistance 50 Ω (8m)
and inductance 0.3 H. The supply is 415 V, 50 Hz.
Calculate:
(i)
the line current
(ii)
the power factor
(iii) total active and reactive power when the load is delta connected. Draw the
phasor diagram.
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
ELECTRICAL MEASURING INSTRUMENT
Winter-2001
Q.1 (a) Explain different types of controlling systems used in the indicating types of
instruments
Q.1 (b)A PMMC instrument has 1 ohm resistance and gives full scale deflection with 100
mA . calculate the resistance required to be connected in series or parallel with the coil to
measure
(i) 10A
(ii) 300V
Summer-2002
Q.1(a) Discuss the necessity of damping in damping in indicating instrument & explain
eddy current damping .
7M
Q.1(b) PMMC instrument has FSD current of 50 milliampere and 20 ohm resistance.
How the instrument can be converted to
(i) 0-5A range Ammeter
(ii) 0-100V range voltmeter
5M
Winter-2002
Q.1 (a)What are the essential torques of an indicating instrument? Justify their necessity
Q.1 (b) Describe the construction & operation of moving iron attraction type instruments.
Can such instruments be used for a.c. & d.c. ? justify .
Summer-2003
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Q.1(a) Discuss the necessity of damping in damping in indicating instrument & explain
eddy current damping .
7M
Q.1(b) PMMC instrument has FSD current of 50 milliampere and 20 ohm resistance.
How the instrument can be converted to
(i) 0-5A range Ammeter
(ii) 0-100V range voltmeter
5M
Winter-2003
Q.1 (a)A moving coil instrument has a resistance of 10 ohm & gives full scale deflection
when carrying a current of 50 mA . show how it can be adopted to measure voltages upto
750V & current upto 100A.
4M
Q.1 (b) What are the essential requirement of indicating type instrument? Explain each of
them.
5M
Q.1(c) Describe electrodynamometer type instrument in detail.
5M
Summer-2004
Q.1(a) What are the different operating systems required in an instrument? Explain
damping system in detail.
5M
Q.1(b) If a shunt for a moving coil instrument is to have a multiplication factor m, show
that its shunt resistance is given by
Rsh = Rm/ (m-1)
Where
Rm - resistance of the meter
5M
Q.1(c) Find the value of a series resistance to be connected to a basic ‘d’ Arsonval
movement with internal resistance Rm =100 ohm & full scale deflection current is 1mA
for conversion into 0-500 volt
4M
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DEPARTMENT OF ELECTRICAL ENGINEERING
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Winter-2004
Q.1(a) Discuss the classification “Indicating type, Integrating type & Recording type” of
the measuring instruments.
6M
Q.1(b) Explain how the range of a moving coil ammeter can be extended.
2M
Q.1(c) A moving coil instrument has 50 ohm coil resistance & gives maximum
deflection at 5mA. Find the external resistance to be connected in series with the
instrument so as to read upto 300V
5M
Summer-2005
Q.1(a) What are the different types of torques required in indicating type instrument?
Explain damping and its necessity.
7M
Q.1 (b)A PMMC instrument has 1 ohm resistance and gives full scale deflection with 100
mA . calculate the resistance required to be connected in series or parallel with the coil to
measure
(i) 10A
(ii) 300V
5M
Winter-2005
Q.1 (a)Full scale deflection of a moving iron meter is obtained when carrying current of
100mA show how it can be used to measure voltage upto 150V & current upto 20A.
Given that resistance of instrument is 20 ohm.
5M
Q.1(b) Explain the construction of induction types single phase energy meter with its
advantages & disadvantages.
8M
Summer-2006
Q.1(a) What do you mean by indicating, recording & integrating instruments
3M
Q.1(b) A moving coil instrument of resistance 5 ohm, required a potential difference of
75mV to give a full scale deflection . calculate:
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DEPARTMENT OF ELECTRICAL ENGINEERING
(i)
FIRST YEAR ELECTRICAL ENGINEERING
the value of shunt resistance needed to enable the instrument to work as a
ammeter and to give full scale deflection at 30A
the value of the series resistance to allow the instrument to work as a voltmeter
with a full scale reading of 250V.
6M
(ii)
Q.1(c) What do you mean by damping? What are the various methods of damping?
D.C. Machines
SUMMER – 2001
Q. 1) Derive an expression for the induced emf in the armature of a dc machine.
(4m)
2) Explain with suitable diagrams
I) critical resistance of the field circuit of a dc shunt generator and
II) critical speeds of the generator .
(4m)
3) The armature of a four pole , lap wound shunt generator has 120 slots
with 4 conductors per slot . The flux per is 0.05 wb. The armature
resistance
is 0.05? and the shunt field resistance is 50 ? . Find the speed of the machine
when supplying 45 A at a terminal voltage of 250V .
(5m)
4) A four pole , 220 V dc series motor has a wave connected armature with
1200
conductors. The flux per pole is 20X 10 -3 wb, when the motor is drawing
46A .
Iron and Friction losses amount to 900W . Armature and series field
resistance
are 0.25 and 0.15 ? respectively . Find
I) the speed II) total torque III) shaft power ,
IV) shaft torque , and V) the efficiency .
(7m)
5) Draw the torque – speed and torque – armature current characteristics of a
dc shunt,
Series and compound motors.
(6m)
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WINTER - 2001
Q. 1) Starter is necessary for dc. motor . Justify the statement. Explain the 3- points
starter .
2) A230V , 4 – pole , dc shunt motor running at 750 gives 7.46 kw with an
armature current
of 38A and field current of 1A. The armature is wave wound and has 400
conductors.
The resistance of armature winding is 0.2 ? and the drop at each brush is 1V
Calculate the
I) the useful torque II) total torque
III) useful flux / pole IV) rotational losses
V) efficiency.
(6m)
3) Draw the torque speeds characteristic of the
I) dc shunt motor II) dc series motor , Comment on it.
(4m)
4) State the condition for the Buildup of a shunt ( dc) generator.
5) Draw the external characteristics of all the dc generator
SUMMER – 2002
Q.) 1) What is the significance of critical resistance as related to the shunt generator?
Show it on its related characteristics.
(4m)
2) A dc series motor is not recommended to the started without load. Why ?
(3m)
3) A four pole lap wound shunt generator delivers 200 A at terminal voltage
Of 250 volts . It has a field and armature resistance of 50 and 0.05? respectively.
Neglecting bush drop , determine .
I) armature current ,
II) current in each conductor.
III) emf induced ,
IV) Power developed .
(6m)
4) Derive necessary relation to prove that torque developed by dc motor is a function
of
Flux / pole and armature current.
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5) A dc shunt motor supplied at 200V runs at 500 rpm. While taking armature current
of
30 amperes. The armature resistance is 0.5 ? . Calculate the resistance required in
series
with the armature to reduce the speed to 300 rpm. Assume the current remaining
same. (7m)
WINTER - 2002
Q.) 1) Explain the function of different part of dc generator.
(6m)
2) A 4- pole dc shunt generator with shunt field resistance of 100 ? and an
armature resistance
of 1 ? has 378 wave – connected conductor in its armature. The flux per pole is
0.02 wb.
If load resistance of 10 ? is connected across the armature terminal and the
generator is
Driven at 1000 rpm. Calculate the power absorbed by the load .
3) Write short notes on:
(I) Significance of back emf of dc motor.
(II) Necessity of starter in case of dc motor.
(3m)
4) A 230 V dc shunt motor has an armature resistance of 0.5 ? and field resistance
of 115 ?
At no load speed is 1200 rpm. and the armature current 2.5 amp. Determine the
line current
And power input when the motor delivers rated load.
(7m)
SUMMER – 2003
Q.) 1) What is the significance of critical resistance as related to dc shunt generator ?
Show It on its related characteristic.
(4m)
2) A DC series motor is not recommended to be started without load. Why?
(3m)
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3) A four pole lap wound shunt generator delivers 200 A at terminal voltage
of 250 volts . It has a field and armature resistance of 50 and 0.05?
respectively.
neglecting bush drop , determine .
I) armature current ,
II) current in each conductor.
III) emf induced ,
IV) Power developed .
(6m)
4) Derive necessary relation to prove that torque developed by dc motor is a
function of
Flux / pole and armature current.
(6m)
5) A 220 V .dc shunt motor runs at 500 rpm. when the armature current is 50A ,
calculate the speed if the torque is doubled.
Given that Ra = 0.2 ?
(7m)
WINTER – 2003
Q.) 1) Derive an expression for the induced emf of a dc generator.
(5m)
2) The following figures given the open circuit characteristic of a dc shunt
generator running at 300 rpm.
Field current (A)
Armature voltage (V)
0
2
3
7.5
92
132
4
162
5
183
6
190
7
212
Determine the voltage to which machine will excite if field circuit resistance
is 40 ohm and
run at 375 rpm.
I) What additional resistance would have to be inserted in the field circuit to reduce
the voltage to 200V At 375 rpm?
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II) Without additional resistance determine the load current supplied by generator
when its terminal
Voltage is 200V . Ignore armature reaction and assume speed to be constant.
Armature resistance is 0.4 ohm.
(8m,)
3) A 4- pole , 200 V wave connected dc shunt motor given 11.19 kw when running at
1000 rpm and
Drawing armature and field current of 50 A and 1A respectively . It has 540
conductors.
Its armature resistance is 0.1 ohm assuming a drop of 1 volt per brush, find:
I) the useful torque
II) total torque
III) useful flux / pole
IV) rotational losses
V) efficiency.
(8m)
4) “ A dc series motor should never de started without some mechanical load on
it” Justify.
(3m)
5) Derive the condition for maximum power developed in dc motor.
(2m)
SUMMER - 2004
Q.) 1) Classify D.C. Generators and D.C. Motors.
2) A 4 pole shunt generator with a lap wound armature resistance of 0.1 ? and
field circuit
resistance of 50 ? The generator supplies sixty 100V , 40 W lamps . Find the
current
in each armature conductor and the generator emf . The brush contact drop is 1
volt / brush.
(8m)
3) Derive a torque equation of a D.C. motor.
(5m)
4) A 200 volt shunt motor has an armature resistance of 0.4? and field resistance
of 200 ?
the motor runs at 750 rpm and taken an armature current of amp. Assuming that
the
load torque remains constant. Find the reduction in fiend resistance necessary
to reduce
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DEPARTMENT OF ELECTRICAL ENGINEERING
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the speed to 500 rpm. Neglect saturation.
(8m)
WINTER – 2004
Q.) 1) The terminal voltage of a DC shunt generator decreases with the increasing
load.
(5m)
Explain.
2) A 250Vdc shunt motor has field resistance of 125 ohms and armature resistance
of 1 ohm. It taken an armature current of 25 A at a speed of 900 rpm. It is
required to increase
the speed to 1100 rpm. keeping the torque constant. Fiend the additional
resistance of the field
to achieve this speed . Assume that the magnetic circuit is unsaturated.
(8m)
SUMMER – 2005
Q.) 1) Classify d.c. generators according to the manner in which field winding is
excited .
Draw figures and write their voltage equations.
(6m)
2) A 250 volt d.c. machine has armature and field resistance of 0.06? and 100 ?
respectively
Determine the total armature power developed when working
I) as a generator delivering 25kw output and
II) as a motor taking 25kw input.
(7m)
3) Explain the principle and operation of d.c. motor. State how unidirectional
torque is developed in
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d.c. motor . What is the significance of back emf?
(6m)
4) A 230 V d.c. shunt motor runs at 800 epm and tokens armature current of 50 A .
Find resistance to be
added to the field circuit to increase speed to 1000 rpm at an armature current of
80A. Assume flux
proportional to field current. Armature resistance = 0.15 ? and field winding
resistance = 250 ?.
(7m)
WINTER – 2005
Q.) 1) A 500V dc shunt motor runs at its normal speed of 300 rpm when the armature
current is 250A.
The resistance of armature is o.16? . Calculate speed when an additional
resistance is inserted in the
Field circuit reducing the shunt field to 80% of normal value and armature
current is 100A.
(7m)
2) What are the different methods to control the speed of dc series motor ?
Explain any one method.
(3m)
3) Derive the expression for torque developed in a dc shunt motor.
(3m)
4) What are the different types of dc generators? Derive the emf equation of this
machine.
(4m)
5) A 4- pole dc shunt generator with shunt field resistance of 100 ? and an
armature resistance
of 1 ? has 378 wave – connected conductor in its armature. The flux per pole is
0.02 wb.
If load resistance of 10 ? is connected across the armature terminal and the
generator is
diven at 1000 rpm. Calculate the power absorbed by the load .
(9m)
SUMMER – 2006
Q.) 1) Explain the principle of operation of dc generator , considering simple loop
generator.
(5m)
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DEPARTMENT OF ELECTRICAL ENGINEERING
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2) A shunt generator delivers 195 A at terminal potential difference of 250V. The
armature
resistance and shunt field resistance are 0.02 and 50 respectively . The iron and
friction
losses equals 950 watt.
Find : I) EMF generator
II) Cu losses
III) output of the prime mover IV) Commercial , mechanical and
electrical efficiencies.
(8m)
3) Draw speed – torque characteristic for following motor:
I) DC shunt motor
II) DC series motor
III) Cumulative compound motor IV) Differential compound motor.
(4m)
4) “DC Series motor is always started with some load connected to it,” Justify.
(3m)
5) A 250V dc shunt motor has armature resistance of 0.25? , on load it takes
armature current of
50 Amp and run at 750rpm. If the flux of motor is reduced by 10% without
changing the load
torque find the new speed of the motor.
(6m)
TRANSFORMER
SUMMER – 2001
Q.1
Derive an EMF equation for a single phase, two winding transformer.
(4m)
Q. 2 Mention the condition for maximum efficiency and state the different losses in case
of the transformer .
(3m)
Q.3. Obtain the equivalent circuit of a 200/400 V , 50 H, single phase transformer from
the following test data :O.C. test (LV side) : 200 V , 0.7 A , 70 W
S.C. test (HV side) : 15 V, 10 A , 85 W.
Calculate the secondary voltage when delivering 5kW at 0.8 p.f. lagging , the primary
voltage being 200V.
(7m)
Q.4 A single phase transformer has 350 primary and 1050 secondary turns. The net
cross section area of the core is 55cm2. If the primary winding be connected to a 400 V,
50 Hz, single phase supply , calculate.
i.
the maximum value of flux density in the core and
ii.
the voltage induced in the secondary winding.
(4m)
Q. 5 . A 25 kVA, single phase transformer , 2200 V to 220V , has a primary resistance of
1 ohms and a secondary resistance of 0.01 ohms . Find the equivalent secondary
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
resistance and the full load efficiency at 0.8 p.f. if the iron loss of the transformer is 80%
of the full load Cu loss.
(6m)
Q.6. Define equivalent resistance leakage reactance of a transformer.
(3m)
WINTER – 2001
Q.1. Show that mutual flux in a transformer remains nearly constant from no-load to full
load.
(5m)
Q.2. A 4 kVA , 200/400v, 50 hz, single phase transformer gave the following results :O.C. test: 220V , 0.7 A, 60W on lv side
S.C. test : 22V, 10 A, 120 W on hv side
Determine the efficiency of transformer at full load with pf 0.8 lagging. Assume, iron
losses vary approximately as the square of flux density.
(8m)
Q.3.
Draw the phasor diagram of a transformer at a lagging load with pf 0.8 leading.
(4m)
SUMMER – 2002
Q.1 Stating the idealizing assumptions , show that for a single phase transformer
E1
N1
=
E2
I2
=
N2
I1
How are the impedance transferred to other side ?
(7m)
Q.2 A 400/200 V, single Phase transformer is supplying a load of 50 Amp. At the power
factor of 0.866 lagging .The no-load current is found to be 2 amp at 0.208 p.f.
lagging.
Q.3 Discuss OC and SC test on a single phase transformer .
(6m)
Q.4 A 5 KVA, 250/500 V, 50 Hz, single phase transformer gave following test data :No Load
Short circuit.
250 V
9V
0.75A
6A
60 W
22W
(LV side)
(HV side)
Calculate :
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DEPARTMENT OF ELECTRICAL ENGINEERING
i.
ii.
iii.
FIRST YEAR ELECTRICAL ENGINEERING
The magnetizing current and the components corresponding to iron loss at
normal voltage and frequency.
The efficiency at full load unity p.f.
The corresponding terminal voltage on full load at 0.8p.f. lagging.
(9m)
WINTER – 2002
Q.1. Explain the working of transformer from no load to full load condition. (6m)
Q.2. A transformer has a primary winding of 800turns and secondary winding of
200 turns . when the load current on the secondary is 80 amp at 0.8 power factor lagging ,
the primary current is 25 amp, at 0.707 power factor lagging . Determine the no-load
current of the transformer and its phase with respect to the primary voltage.
(7m)
Q. 3. Draw the phasor diagram of single phase transformer for capacitive load with
the effect of magnetic leakage.
(7m)
Q. 4. A 4 kVA , 200/400 Volts, 1- phase transformer has equivalent resistance and
reactance referred to low – voltage side equal to 0.5 Ω and 1.5 Ω respectively. Find the
terminal voltage on the high –voltage side when it supplies ¾ th of full load at power
factor of 0.8, the supply voltage being200V. Hence , find the output of the transformer
and its efficiency if the core losses are 100 watt.
(9m)
SUMMER – 2003
Q. 1 Explain the working principle of single phase transformer and derive an emf
equation for the same.
(7m)
Q. 2 A 400/200 V, single phase transformer is supplying a load of 50 amp. At the
power factor of 0.866 lagging.
The no-load current is found to be 2 ampere at 0.208 pf lagging.
Calculate the current and power factor on primary side of transformer . Draw the phasor
diagram.
(6m)
Q. 3 Discuss OC and SC test on a single phase transformer .
(6m)
Q. 4 A single phase , 4kVA, 200/400 V , 50Hz transformer has been tested for open
circuit and short circuit and following test results are obtained :OC test :200 V, 1 amp, 100 W on LV side
i.
SC test :- 15 V, 10 amp , 80 W on HV side .
Find all the parameters of equivalent circuit and draw the equivalent circuit
referred to primary side.
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DEPARTMENT OF ELECTRICAL ENGINEERING
ii.
iii.
FIRST YEAR ELECTRICAL ENGINEERING
Determine full load regulation of transforemer at 0.8 p.f. lagging load current
.
Determine efficiency at full load , and U.P.F.
(8m)
WINTER – 2003
Q. 1 Describe open –circuit test and short circuit test on 1-phase transformer.
(5m)
Q. 2 The equivalent circuit for a 200/400 V transformer has the following
parameters referred to low voltage side :Equivalent resistance = 0.15 ohm
Equivalent reactance = 0.37 ohm
Core-loss component resistance = 600ohm
Magnetizing reactance = 300 ohm.
When the transformer is supplying a load at 10 A at a power factor of 0.8 lagging
calculate :
(1) The primary current.
(2) The secondary terminal voltage.
(8m)
Q. 3 ) A 250/500V transformer gave the following test results :SC Test : With low voltage winding Short – circuited : 20V, 12A, 100 W.
OC Test : 250V , 1 A , 80W on low voltage side .
Determine the equivalent circuit constants , insert these on equivalent circuit diagram
and calculate applied voltage and efficiency when the output is 10 A at 500 volt and 0.8
power factor lagging .
(9m)
Q. 4. ‘Transformer is a constant flux device’. State true or false and justify.
(4m)
SUMMER –2004
Q.1) Explain the working of transformer on load.
Q.2) Draw phasor diagram for Ideal Transformer.
Q.3) Derive the expression for condition of “Maximum efficiency “ of 1-φ Trasformer.
Q.4) Draw phasor diagram of practical transformer for lagging p.f
Q.5) The following test data is obtained on 5 KVA ,220/440 volts , single phase
transformer :
O.C. Test : 220 V, 2 Amp, 100 W…….L.V. Side
S.C. Test : 40 V,11.4 Amp ,200 W ……H.V Side
Determine :
i)
% efficiency at full load 0.9 p.f. lag .
ii)
% efficiency at half load unity p.f.
iii)
Regulation at 0.8 p.f. lagging.
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
Winter- 2004
Q.1) Discuss short circuit and open circuit tests for a single phase transformer
Q.2) A Single phase, 10 KVA, 500/250V,50 Hz transformer has the following constants:
R1= 0.2 ohm R2 = 0.1 ohm
X1 = 0.4 ohm X2 = 0.2 ohm .
The resistance and reactance of equivalent exciting circuit referred to primary are
R0 = 1500 ohm
X0 = 750 ohm .
What would be the readings of instruments (placed in primary) When the transformer is
connected for open circuit and short circuit tests?
Q.3) A single phase transformer is rated 600/200 V ,25 KVA ,50 Hz.
i)
Calculate the magnitude of primary and secondary currents when transformer
is fully loaded.(Assume ideal Transformer)
ii)
What should be the impedance of the load in ohms to fully load the
transformer when connected on : (a) 600 V side (b) 200 V side. .(Assume
ideal Transformer)
iii)
What would be the value of the maximum core flux when the transformer is
excited at rated voltage on either side , given N1 = 60 turns?
iv)
If the 600 V side is excited at 600 V ,40 Hz , What would be the core flux and
secondary voltage?
Q.4) A 100 KVA, 6600/330 V, 50 hz ,single phase transformer takes 10 A ,436 W at
100V in a Short circuit test , the figures referring to h.v. side. Calculate the voltage to be
applied to the h.v. side on full load at a p.f. of 0.8 lagging when the secondary terminal
and voltage is 330 V
SUMMER – 2005
Q. 1
‘Transformer is a constant flux device’ justify.
(4m)
Q. 2. ‘In transformer , open circuit test gives iron losses and short circuit test gives
copper losses’. Justify.
(3m)
Q. 3. A single phase transformer has 1000 turns on the primary and 200 turns on the
secondary . The no load current is 3 amp. At a power of 0.2 lagging . Calculate the
primary current and power factor when the secondary current is 280 Amp at a power
factor of 0.80 lagging.
(6m)
Q. 4.
Derive the condition for maximum efficiency of transformer .
(6m)
Q. 5 . The test result obtained from open and short circuit test on 10 kVA, 450/120 volt,
50Hz 1-Phase transformer are :
O.C. Test :
120 volt; 402 Amp: 80 watts – one low voltage side.
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
S.C. Test :
9.65volt, 2202 amp : 120 watts –on the high voltage side.
Calculate:1 The equivalent circuit constants.
2 Efficiency and voltage regulation for full load 0.8 power factor lagging.
(9m)
WINTER – 2005
Q. 1. ‘Transformer is a constant flux device’ justify.
(6m)
Q. 2.
A 3300/300 V single phase transformer gives 0.6 A and 60 W as ammeter and
wattmeter reading when input voltage is given to low voltage winding and high voltage
winding is kept open , Find:
1. pf of no load current .
2.
magnetizing component of input current.
3.
iron loss component of input current.
(7m)
Q.3: A 4 KVA ,400/200 Volts ,50 Hz, single phase transformer has the following test
data:
OC TEST: 200 V,1 Amp, 64 W (LV side)
SC TEST: 15 V,10 Amp, 80 W (HV side)
(8M)
Determine the equivalent parameters as referred to lv side .Also calculate the secondary
terminal voltage on Full load at 0.8 pf lagging.
Q.4: Define energy efficiency
Q.5: Derive the condition for maximum efficiency of transformer
(2M)
(3M)
SUMMER 2006
Q.1: In making the core joints of the laminations are places in alternate
layers. Why
(2 M)
Q.2: In practical transformer, half of the primary and half of the secondary is
placed on the side limb. Why
(2 M)
Q.3: While performing OC test, why the HV winding is generally kept open
circuited?
(2M)
Q.4:”If the core is laminated eddy current losses decreases”. Justify.
(2M)
Q.5: A transformer has a primary winding of 800 turns and secondary
winding of 200 turns. In the load current on the secondary is 80 ampere
at 0.8 pf lagging. The primary current is 25 Amp. at 0.7 pf lagging.
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DEPARTMENT OF ELECTRICAL ENGINEERING
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Determine the no load current and its power factor.
(6 M)
Q.6: The instrument readings obtained from open and short circuit test on
10 KVA, 415/120 V,50 Hz transformer are
O.C test: 415 V, 1.12 AMP,80 W (Read on high voltage side)
S.C test: 2.6 V, 83.25 Amp.120 W (With high voltage winding short
circuited) .
Compute:
(1)Full load efficiency and voltage regulation at 0.8 pf lagging
(2) Half load efficiency and voltage regulation at unity pf lagging
(3) Draw the equivalent circuit
(8M)
Q.7: Explain short circuit test on transformer.
(5M)
THREE PHASE & SINGLE PHASE INDUCTION MOTOR
SUMMER-2001
Q1) Draw and explain the torque- slip characteristics of a 3-phase I.M. (3m)
Q2) Derive the a general expression for the torque developed in a 3-phase
I.M.
Q3) The power to a 400V, 60Hzs ,6 pole 3-phase I.M. running at 1140 rpm.
Calculate: (i) slip
(ii) Synchronous speed
(iii) Frequency of rotor current.
(6m)
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(4m)
DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
WINTER-2001
Q4) Define slip of 3-phase I.M.
(2m)
Q5) Three phase 400v, 50Hzs, I.M. has a speed of 950 rpm on full load. The
motor has 6 poles. Calculate (i) how many complete alternations will
the rotor voltage make per second?(ii)speed of rotor field with respect
to rotor core.
(6m)
Q6) For I.M. prove the relation
Input power to rotor : mechanical power developed : rotor copper
losses= 1 : (1-s) : s
(6m)
Q7) Single phase I.M. is not a self starting motor. Explain.
(7m)
Q8) Draw the torque speed characteristics of the 3- phase I.M. Comment on
it.
(6m)
SUMMER-2002
Q9) The slip ring I.M. is preferred to the squirrel cage I.M. for the load
needing high starting torque, Justify.
Q10) Explain the torque- slip characteristics of a 3-phase I.M.
(3m)
(5m)
Q11) A 3-phase I.M. IS wound for 4 poles & is supplied from 50Hzs,
system. Calculate
i) Synchronous speed
ii) Speed of rotor when the slip is 4%
iii) Rotor frequency when the speed of the motor is 1400rpm.
(5m)
WINTER-2002
Q12) Derive the torque equation of 3 phase I.M. also draw the torque- speed
characteristics of this motor.
(6m)
Q13) Why the maximum torque of 3 phase I.M. is independent of rotor resistance.
(2m)
Q14)What are the types of 3 phase I.M. Explain any one type of 1-phase I.M. What are
the applications of 1- phase I.M.
(5m)
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
SUMMER 2003
Q15)The slip ring I.M. is preferred to the squirrel cage I.M. for the load
needing high starting torque, Justify.
(4m)
Q 16)Explain the torque- slip characteristics of a 3-phase I.M.
(5m)
Q17) A 3-phase I.M. IS wound for 4 poles & is supplied from 50Hzs , system. Calculate
ii) synchronous speed
iii) speed of rotor when the slip is 4%
iii) rotor frequency when the speed of the motor is 1400rpm.
(5m)
WINTER-2003
Q18) “ AThree phase I.M. can not run at synchronous speed, Justify.(4m)
Q19) A 4 pole , 3- phase , I.M. operates from a supply whose frequency is 50Hzs.
Calculate
i) speed of rotor when the slip is 0.04
ii) the speed at which the magnetic field of the stator is rotating .
iii)The frequency of rotor currents when the slip is 0.03.
iv) The frequency of rotor currents at standstill.
(6m)
Q20) Write short note on capacitor start Induction run 1Ф I.M.
(4m)
SUMMER 2004
Q21) Explain the principle of operation of 3 phase Induction Motor.
(5m)
Q22) A 3-phase 50 Hz, I.M. has a slip of 4 %. Calculate
i)Speed of the motor (ii) frequency of rotor emf
iii)If the rotor has resistance of 1 ohm and standstill reactance of 4 ohm, Calculate p.f at
standstill and a speed of 1400 rpm.
(8m)
WINTER 2004
Q 23) Sketch and Explain the torque- slip characteristics of a 3-phase
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
I.M.What is the effect of changing rotor resistance on the above
characteristic ?
(9m)
Q 24) A 6 pole synchronous generator driven at 1000 rpm feeds a 4 pole I.M which is
loaded to run at a slip of 4 %. What is the motor speed ?
(4m)
Q25) Give reasons:
i) the speed of 3- phase IM can not be equal to synchronous speed.
(i)I.M can be called a generalized transformer with rotating secondary.
(ii)In 3 phase I.M , the rotor core loss is negligible.
(iii)The reactance of the rotor in 3 phase I.M varies widely between starting and running
conditions.
(8m)
SUMMER-2005
Q.26) “A Three phase I.M. can not run at synchronous speed, Justify. (4m)
Q.27) A 3-phase I.M. IS wound for 4 poles & is supplied from 50Hzs system. Calculate :
i)The synchronous speed
iii) The speed of rotor when the slip is 4%
iii) The rotor frequency when the speed of the motor is 1400rpm.
(5m)
Q.28) Explain the torque- slip characteristics of a 3-phase I.M.
(4m)
WINTER-2005
Q29) Q1Draw and explain the torque- slip characteristics of a 3-phase I.M.
(4m)
Q30) A 3-phase , 6-pole,50 Hz, I.M. has a slip of 1 % at no load and 30% at full load.
Find:
i) The synchronous speed
ii) No load Speed
(iii) Full load Speed
iv)Frequency of rotor current at standstill
v) Frequency of rotor current at full load.
(5m)
Q31).Explain the working of capacitor start , induction run type 1-phase I.M.
(5m)
SUMMER-2006
Q32) “ Three phase I.M. never attaines the synchronous speed,”.Justify.
(3m)
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DEPARTMENT OF ELECTRICAL ENGINEERING
FIRST YEAR ELECTRICAL ENGINEERING
Q33) A 4 pole , 3- phase , I.M. operates from a supply whose frequency is 50Hzs.
Calculate
i) the speed at which the magnetic field of the stator is rotating .
ii) the speed of rotor when the slip is 0.04
iii)The frequency of rotor currents when the slip is 0.03.
iv) The frequency of rotor currents at starting.
(7m)
Q34) “ 1-phase I.M. is not self starting”. Justify.
G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR
(3m)
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DEPARTMENT OF ELECTRICAL ENGINEERING
G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR
FIRST YEAR ELECTRICAL ENGINEERING
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DEPARTMENT OF ELECTRICAL ENGINEERING
G.H.RAISONI COLLEGE OF ENGINEERING, NAGPUR
FIRST YEAR ELECTRICAL ENGINEERING
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