BHARATHIDASAN ENGINEERING COLLEGE QUESTION BANK
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
YEAR/SEM : I / II
NAME OF THE SUBJECT: EE6201 CIRCUIT THEORY
NAME OF THE FACULTY: A.R. DINESH KUMAR
SYLLABUS
( X ) * Ohm‟s Law - Kirchoffs laws - DC and AC Circuits - Resistors in Series and Parallel
Circuits
( Y ) * Mesh Current and Node Voltage Method of analysis for D.C and A.C. Circuits –
Phasor
Diagram – Power, Power Factor and Energy
PART – A
IX1 Find the equivalent conductance of the circuit shown below
( Nov/Dec 2012)
( April/May 2013)
(April/May 2013)
IX2 State the Limitation of Ohm’s law.
IX3 Determine current in the circuit of fig (April/May 2014)
(April/May 2014)
IX6
IX7
IX8
IX4 Determine the current through 20Ω resister in the circuit of fig ( April/May 2014)
IX5 Find the equivalent resistance of the circuit shown in fig ( May/June 2014)
Define RMS voltage ( May/June 2014)
An electrical appliance consumes 1.2kwh in 30 mins at 120V.what is the current drawn by the appliance?
Nov/Dec 2014) (
Calculate the equivalent resistance between the terminals “a” & “b” in fig
( Nov/Dec 2014)
(April/May 2015)
IX9 Obtain current in the each branch of the network shown below using (April/May2015)
kirchhoff’s current law
IX10 State Kirchoff’s Voltage law (April/May2015)
IX11 (Nov/Dec 2014)
Define ohm’s law
(April/May 2016)
IY9 (ii) ( Nov/Dec 2014)
IX12 Write briefly about resistance in a circuit ( April/May 2015)
IY13 Define mesh analysis of a circuit ( Nov/Dec 2012)
IY14 Distinguish between mesh & loop of an electric circuit. ( April/May 2013)
IY15 Write the expression for mesh current equations in matrix form ( Nov/Dec 2014)
IY16 what are three types of power used in A.C circuit? ( April/May2015)
PART B
Find the equivalent resistance between the terminals “a” & 4
“b” for the network shown in fig
IY7 ( i) Determine the current through each resistor in the circuit 6 May/June (
2014) shown fig
(April/May 2017)
IXI (ii) State and explain kirchoff’s Laws. 6 (April/May2013,
Nov/Dec 2014)
IY4 (i) Three loads A, B and C are connected in parallel to a 240 V source. Load A takes 9.6 KW, Load B takes 60 A and
Load C has a resistance of 4.8 Ω. Calculate (i) (1)𝐴 and 𝑅𝐵(2)
the total current (3) the total power, and (4) equivalent
resistance.
6 (April/May 2013)
IY6 (i) Find the current I and voltage across 30 Ω of the circuit 8 (May/June 2014)
shown in fig
IXI i) ( Determine the current I L in the circuit shown in figure
below:
8 Nov/Dec 2012) (
IY1 ( i) For the circuit shown in figure below, determine the total 8 ( Nov/Dec
2012) current I T , phase angle and power factor.
IY1 (ii) In the circuit given below ,obtain the load current 8 Nov/Dec 2014) (
(April/May 2018)
IY6 (ii) Determine the current in all the resistors of the circuit 8 (May/June 2014)
shown in fig
IY7 (ii) When a dc voltage is applied to a capacitor,voltage across 10 (May/June
2014) its terminals is found to build up in accordance with
IY8 ( i) Derive the expressions for resistors in parallel & series 8 Nov/Dec 2014) (
IY8 ii) ( Two 50Ω resistors are connected in series.when a resistor R is connected across one of them,the total circuit
resistance is 60 Ω.calculate the value of R.if the supply voltage across the above circuit is 60V,find the current passing through individual resistance.
8 ( Nov/Dec 2014)
Y3 Using mesh analysis, determine the current through 1 Ω 10 resistor in the given circuit.
IY4 ( ii) By applying nodal analysis for the circuit shown in Fig, 10 determine the power output of the source and the power in each resistor of the circuit.
(April/May 2019)
vc=50(1-e-100t).After 0.01S the current flow is equal to 2mA.
(1) Find the value of capacitance is farad.
(2) How much energy stored in the electric field?
IY5
IY9 i) ( Using node analysis,find the node voltages &b the currents
through all the resistors for the circuit shown in fig
12 ( Nov/Dec 2014)
IY2 For the circuit shown in the figure, Determine the value of 16 ( Nov/Dec 2012) V 2 such that the current through (3+j4)Ω Impedance is zero.
( i) Determine the currents in all branches 16 ( ) ii Calculate the power & power factor of the source
iii ) ( Show that po wer delivered by the source is equal to power
consumed by 2Ω resistor
(April/May 2020)
IY10 For the circuit shown in fig,find the(i)currents in different 16 ( Nov/Dec 2014)
branches,(ii) current supplied by the battery,(iii) potential
difference between terminals A & B
IY11 Determine the current supplied by each battery in the 16 (April/May 2015)
circuit shown below using mesh analysis
IY12 Use nodal voltage method to find the voltages of nodes ‘m’ 16 ( April/May 2015)
& ‘n’ and curr ents through j2Ω & - j2Ω reactance in the network of fig
Use branch currents in the network shown below to find 16 the current supplied by the 60V source.Solve the circuit by the mesh current method.
(April/May 2021)
IY13
IY14 Solve the network given below by the node voltage method
16 ( April/May 2015)
UNIT II SYLLABUS
(X) * Network reduction: voltage and current division, source transformation - star delta
Conversion.
(Y) * Thevenin’s and Norton & Theorem – Superposition Theorem – Maximum power
transfer theorem – Reciprocity Theorem.
IIX6 How to change the (a) current source into voltage source (b) voltage source
into current source?
(Nov’09)
PART – A
IIX1 State the voltage division principle for two resistor in series and
the current division principle for two resistor In parallel.
( May’13)
IIX2 Find the equivalent current source for a voltage source of 100V
with series resistance of 2 Ω .
( May’12)
IIX3 Find the equivalent current source for the circuit shown in fig
( May’10)
IIX4 Write the objective of star delta transformation.
( Nov’13)
IIX5 For the network shown in the following fig, convert the voltage
( Nov’10) source into current source
IIX7
IIX8
IIX9
IIX10
IIX11
IIX12
IIY13 State Maximum Power transfer theorem.
(May’13,May’10)
IIY14 State Reciprocity theorem. (May’12,Nov’13)
IIY15 State Thevenin’s Theorem.
(May’11)
With example explain the transformation of three voltage source is
in series with three resistance combination? ( Nov’09)
Write the formula for star to delta transformation. ( May’09)
Write the formula for delta to star transformation.
( May’09)
Draw the equivalent current source transformation circuit for
the following circuit.
( Nov/Dec 2014)
Give a delta circuit having resistors, write the required
expressions to transform the circuit to a star circuit.
( Nov’12)
Transform the circuit shown below, from delta to star.
( May’11)
IIY16 In the circuit shown below, find the value of the load impedance
ZL for maximum Power Transfer to the load.
(Nov’12)
IIY17
IIY18
IIY19
IIY20
IIY21
IIY22
IIY23
State Super Position Theorem ( May’10)
State Norton’s Theorem ( May’10)
Draw the equivalent circuit for Norton’s theorem
( Nov09)
Which theorem is used to find the maximum power for a
Linear/nonlinear network?
( Nov’09)
Write the formula for finding the Thevenin’s resistance
( May’09)
Compare Thevenin’s theorem and Norton’s theorem
( Nov’09)
What is the current formula for Maximum power transfer theorem? ( Nov’10)
Which theorem is applicable for linear / bilateral networks?
( Nov’11)
State reciprocity theorem. ( Nov/Dec 2014)
Draw the equivalent circuit for Thevenin’s theorem ( Nov’10)
PART B
IIY12 State and explain superposition theorem. 6
IIY24
IIY25
IIY26
IIX1 (i) Use the technique of delta-star conversion to find the 8 (May’11)
equivalent resistance between terminals AB of the circuit shown below.
IIX1 (ii) Explain the source transformation technique. 8 (May’13)
IIX2 (May’11)
( i) Use source transformation to find I0 in the circuit shown 8
below.
IIX2 (ii) Using source transformation, replace the current source in 8 ( Nov’12) the circuit shown
below by a voltage source and find the current delivered by the 50V voltage source.
IIX5 i) ( Explain the conversion from a star circuit to delta circuit.
8 ( Nov/Dec 2014)
IIX5 ii) ( In the circuit given below, obtain the equivalent resistance at
AD.
8 ( Nov/Dec 2014)
IIY6 i) ( Use the superposition theorem to find the current through 8 May’13) (
4 Ω resistor in the circuit shown in fig.
IIY8 (ii)
IIY9 (i) Determine the voltage across 20Ω resistance in the circuit 8 (May’11) shown below, using
superposition theorem.
IIY6 (ii) Calculate the equivalent resistance Rab when all the 8 Nov’12) ( resistance values are equal
to 1Ω for the circuit shown below.
IIY7 (i) Derive expression for star connected resistances in terms of 8 ( May’13) delta connected
resistances. IIY7 (ii) Find the current trough branch a - b of the network shown in 8 fig. using Thevenin’s
theorem.
IIY8 (i) Calculate the current through 2Ω resistor in the circuit 8 May’12) ( shown in fig, using
superposition theorem.
Calculate the current through 2Ω resistor in the circuit 8
shown in fig using thevenin’s theorem.
IIY12 Find the current through 10Ω resistor in fig, using 10 (Nov’13) Thevenin’s
Theorem.
Q.
IIX3 In the circuit shown below, find 16 ( May’10) ( i) The equivalent resistance between P and
( ii ) The total current from 240V source.
( iii ) The current through 18Ω resistor.
IIX4 Using star - delta transformations, in the following wheat 16 ( Nov’13)
stone bridge circuit of fig, find (i) the equivalent resistance between P and Q, (ii) the total current (iii) The current through
18 Ω resistor.
UNIT III SYLLABUS
(X) * Series and Parallel resonance – Their frequency response – Quality factor & Bandwidth
(Y) * Self and Mutual inductance – Coefficient of coupling – Tuned circuits – Single tuned
circuits.
PART – A
IIIX1 Define band width of a resonant circuit. (May’13,May’09)
(Nov/Dec 2014)
IIIX2 Define Resonant network. (May’12)
IIIX3 When do you say that a given AC circuit is at resonant? (May’11)
IIIX4 In a series RLC circuit, If the value of L and C are 100Uh and
o.1Uf respectively. Find the resonance frequency in HZ (May’10)
IIIX5 Define quality factor of a coil (May’09)
IIIX6 Write the significance of quality factor. (Nov’13)
IIIX7 A series resonant circuit has a bandwidth of 20KHz and a (Nov’12) quality
factor of 40. The resistor value is 10 Kohm. Find the
value of this circuit
IIIX8 Write the condition of resonance (Nov’11)
IIIX9 Draw the series resonance, parallel resonance circuits and phasor
diagram. (Nov’11)
IIIX10 Compare series and parallel resonance circuits. (May’11)
IIIX11 Determine the value of capacitive reactance and impedance at
resonance. When R = 10ohm, C =25µF and L =10Mh (Nov’10)
IIIX12 Mention the relationship between Q-factor and bandwidth
(May’10)
IIIX13 What is resonance frequency and Bandwidth of a series RLC
circuit in which R=5ohm, L=40Mh, C=1µF?
(Nov’09)
IIIX14 Draw the frequency response of R-L circuit and explain.
(May’11)
IIIX15 What do you understand by damped frequency? (Nov’10)
IIIX16 In a parallel RL circuit R=3ohm and XL =4ohm.What is the
( Nov’12)
( Nov’10)
( Nov’10)
( May’11)
value of admittance?
IIIY17 Give the applications of tuned circuits.
(May’13)
IIIY18 State ‘Dot rule’ for coupled circuits
IIIY19 Two inductively coupled coils have self inductances L1=50 mH
and L2=200 mH. If the coefficient of coupling is 0.5, Compare the value of mutual inductance between the coils.
(May’11)
IIIY20 Write the empirical formula for coefficient of coupling in coils. (Nov’13)
IIIY21 Define Mutual inductance.
IIIY22 Define coefficient of coupling?
IIIY23 What is the maximum possible mutual inductance of two
Inductively coupled coils with self-inductance L1=25mH and L2=100mH?
IIIY24 Two inductively coupled coils have self-inductance L1=45 mH and
L2=150 mH. If the co-efficient of coupling is 0.5, (i) find the value
of mutual inductance between the coils and (ii) what is the
maximum possible mutual inductance?
PART B
IIIX6 (ii) State the concept of bandwidth of a series RLC circuit. 2
IIIX6 (iii) A series RLC circuit consists of 50 ohm resistance, 0.2 4
H inductance and 10 uF capacitance with the applied voltage
of 20 V. Determine the resonant frequency, Q factor, the
lower and upper frequency limits and the bandwidth of the
circuit.
IIIX1 (i) Derive the resonance frequency ‘f’,for the circuit shown 8 (May’13)
in fig
IIIY10 (i) In the coupled circuit shown below. Find the voltage across 5 8 (May’11)
ohm resistor.
IIIX1 ( ii) A series circuit with R=10 ohm, L=0.1H and C=50uF has
an applied voltage V=50 V with a variable frequency. Find
( i ) the resonant frequency (ii) the value of frequency at
which maximum voltage occurs across inductor (iii) the
value of frequency at which maximum voltage occurs
across capacitor (iv) the quality factor of the coil.
8
IIIX2 ( i) The signal voltage in the circuit shown in fig is
e(t)=0.01 sin ( 2 𝜋 ∗ 455∗10 3 𝑡 ) V.What should be the
value of C in order that the circuit would resonant at this
signal frequency? At this condition, find the values of
I,Vc,Q and bandwith of the circuit.
8 ( May’12)
IIIX2 ii) ( RL+20)ohm and ( (20 - j10) ohm are connected in parallel .
Determine the value of RL for resonanace.
8
IIIX3 ( i) For the tank circuit shown below, find the resonance frequency
fr.
8 May’11) (
IIIX3 ii) ( Determine the quality factor of the coil for the series circuit
consisting of R=10 ohm, L=0.1 H and C=10 uF. Derive the
formula used.
8
IIIY14 (ii) Two coupled coils have self inductances of L1=100 mH
and L2=400 mH. The coupling coefficient is 0.8. Find M.
If N1 is 1000 turns, what is the value of N2? If a current
i1=2 sin(500t) A through the coil 1, find the flux and the
mutually induced voltage V2m.
8
IIIY15 (i) Co-efficient of coupling. 8 (Nov/Dec 2014)
IIIY15 (ii) Tuned circuit 8
IIIY10 ( ii) Derive the expressions for maximum output voltage and
maximum amplification of a single tuned circuit.
8 ( May’11,
Nov’13)
IIIY11 i) ( Derive the expression for coefficient of coupling in terms
of mutual and self inductances of the coils.
8 13) ( May’
IIIY11 ( ii) Consider the single tuned circuit shown in fig. determine
( a) the resonant frequency (b) the output voltage at
resonance (c) the maximum output voltage. Assume RS>>
wrL1 and K=0.9.
8 ( May’13,
May’12)
IIIY14 ( i) Obtain a conductively coupled equivalent circuit for the 8 ( Nov’12)
magnetically coupled circuit shown below.
IIIX6 (i) Derive the resonance frequency fr for the circuit below. 10 (Nov’12)
UNIT IV SYLLABUS
(X) * Transient response of RL, RC and RLC Circuits using Laplace transform for DC input
IIIX7 A RLC series circuit has R=60 ohm,L=160 mH and C=160
uF. Find the resonant frequency under resonant condition
obtain the current, power and the voltage drop across the
various elements if the applied voltage is 300V.
16 Nov’13) (
IIIX8 For a series RLC circuit 16 Nov/Dec 2014) (
( i) Derive the condition for resonance
( ii) Explain the frequency response and
( iii) Obtain the quality factor and bandwidth
IIIY9 Derive the relationship between self - inductance , mutual
inductance and coefficient of coupling.
16 May’12, (
May’10)
IIIY12 In the circuit shown in fig, find the value of I1 and I2 and
also the real power supplied by each source.
16 ( May’10)
IIIY13 Explain the single tuned and double tuned circuit. 16 ( May’09)
(Y) * Transient response of RL, RC and RLC Circuits using Laplace transform for A.C. with
sinusoidal input – Characterization of two port networks in terms of Z,Yand h
parameters.
PART – A
IVX1 What is meant by transient time? (Nov’13)
IVX2 Compare steady state and transient state (Nov’11)
IVX3 A series RL circuit with R=100 ohm and L=20 H has a dc
Voltage of 200V applied through a switch at t=0. Assuming (May’10)
the intial current through the inductor t=0 is zero, find the
current at t=0.5 sec.
IVX4 Draw the DC response of R-L circuit and the response curve.
(May’11)
IVX5 Draw the DC response of R-C circuit and the response curve (May’11)
IVX6 Draw the DC response of R-L –C circuit and the response (Nov’10) curve
IVX7 Write the purpose of Laplace transformation in the circuit
Analysis. (Nov’13)
IVX8 Write any two advantages of laplace transformation. (Nov/Dec 2014) IVX9
Define damping ratio?
(May’11)
IVX10 Find the time constant of RL circuit having R=10 ohm and
L=0.1 mH. (May’13)
IVX11 Define transient,forced response (Nov’11)
IVX12 What is the condition to be present in a series RLC circuit to (May’10,Nov’12)
make the circuit critically damped?
IVX13 A RLC series circuit has R=10 ohm, L=2 H. What value of
capacitance will make the circuit critically damped? (May’13)
IVX14 Define the term ‘Time Constant’ of a circuit, in general.
(May’11)
IVY15 Write the expression for the laplace transformation of sine
function, (sin ωt).
(Nov/Dec 2014)
IVY16 Sketch the current given by i(t)= 5 – 4 e-20t.
(May’11)
case
in
the
two
cases.
IVY21
Calculate the impedance.
IVY22
Circuit.
IVY23
IVY24
conditions
PART B IVX1 Derive the transient response of
series RLC
(May’12) circuit, with DC input, using Laplace transform
(a) Derive the necessary differential equation and solve. 4
(b) Discuss the cases of over damping, critical and 4 under damping.
IVY17 Draw the sinusoidal response of R-L -C circuit and write the
differential equation
(May’10)
IVY18 Draw the sinusoidal response of R-C circuit and write the
Differential equation.
(May’10)
IVY19 Draw the sinusoidal response of R-L circuit and write the
Differential equation.
(Nov’10)
IVY20 Consider two cases RC parallel circuit shown below. First
When DC voltage is applied and second case when AC
voltage is applied. Compare how the capacitor gets charged ( May’12)
A coil having a resistance of 10 Kohm and inductance of 50
mH is connected to a 10 V, 10 KHz power supply. ( May’11)
Sketch the transient current i(t) vs t graph for a series RL
( May’12)
Determine Laplace transform for the unit step function u(t). ( Nov’12)
Write the steps to be involved in the determination of initial ( Nov’12)
(c ) Express the solution in terms of undamped 4
natural frequency, damped natural frequency and
damping factor.
(d) Sketch the transient response curve for the three cases. 4
IVX2 (i) Using Laplace transform, obtain the expression for i1 and i2 8
(May’11) in the circuit shown below, when dc voltage source is applied
suddenly. Assume that the initial energy stored in the circuit is zero.
(ii)
In the circuit shown in fig,find the expression for the 8 transient current ,the initial current is as in fig
Derive the transient response of a series RL circuit with DC 8
( Nov’12) input. Sketch the variation of current and of the voltage across the
Solve for I and V as functions of time in the circuit shown 8 Below , when the switch is closed at time t=0.
IVX5 A series RL circuit with R=30Ω & L=15H has a constant 16 May/June 14 Voltage V=60v applied at t=0 as shown in fig. Determine the current I, the voltage across resistor and the voltage across the inductor .
IVX6 The circuit shown in fig consists of R,L & C in series with 16 May/June 14 V DC when the switch is closed at t=0.find the current 100
transient.
IVX4 (i)
inductor.
(ii)
IVX3 In the circuit shown in fig, the switch S is closed at time t=0 16
(Nov’13, May’10) in position 1 and changed over to position 2 after 1msec.
Find the time at which the current is zero and reversing its
direction. Assume that the changeover of switch from
position 1 to 2 takes place in zero time.
IVX7 Derive the step response of RL and RC circuits. Compare 16 (May’13)
their performances.
IVY8 Derive an expression for the current response of
RLC series circuit with sinusoidal excitation. Assume
that the circuit is working in critical.
IVY9 Derive an expression for the current response of
RLC series circuit with sinusoidal excitation. From the
results, discuss the nature of transient and steady state
responses. Comment on the phase angle involved.
IVY10 In the circuit shown in fig, find the expression for current if 16
(Nov’13,May’10) the switch is closed at t=0 and the value of current at t=1 msec.
Assume initial charge on the capacitor is zero.
IVY11 Derive the expression for the complete solution of the current 16 (Nov’12) response of RC series circuit with an excitation of Vcos(wt+fi ). Briefly explain the significances of phase angle in the solution.
IVY12 A series RL circuit with R=100 ohms and L=1 H has a 16 (Nov/Dec 2014)
sinusoidal voltage source 200sin (500t+φ) applied at a time
when φ=0. (i) Find the expression for the current. (ii) at what
value of angle φ must the switch be closed so that the current
directly enters the steady state. (16)
IVY13 Explain in detail with neat illustrations the high pass & low
pass networks and derive the necessary network parameters
16 April/May 2015
IVY14
Explain the characterization of two port networks in terms of
Z,Y & h parameters
16 April/May 2015
UNIT V SYLLABUS
(X) * Three phase balanced / unbalanced voltage sources - analysis of three phase 3-wire
and 4-wire circuits with star and delta connected loads, balanced & un
balanced - Phasor diagram of voltages and currents
(Y) * Power and Power factor measurements in three phase circuits.
16 ( May’13)
16
3Φ,50Hz supply. Calculate phase voltage. Ia=10 -
VX8
VX9
What is the difference between balanced and unbalanced
circuits?
Explain how to solve unbalanced neutral isolated three phase load
connected to a balanced supply?
120 A,
Ib=5
150 A.
(Nov’11) What is
the line
current (May’11)
Ic?
VX10 What is meant by positive, negative, zero sequence
VX6
VX7
Write the current relations in star and delta connections of a
three phase circuit.
Three inductive coils each having resistance of 16 Ω and
(Nov’13)
reactance of j12 Ω are connected in star across a 400V, (Nov’12)
PART – A
VX1 What is a phase sequence of a 3 - phase system?
May’13) (
VX2 A delta connected load has (30 - j40) Ω impedance per phase.
Determine the phase current if it is connected to a 415V, 3Φ, and 50Hz supply.
( May’13)
VX3 What are the advantages of 3 - phase systems?
May’13,Nov’13) (
VX4 A 3Φ, 440V supply is given to a balance star connected load of
impedance (6 - j8)Ω in each branch. Find the magnitude of the line current.
( May’12)
VX5 In the circuit shown in fig, find the rms value of line current
and phase voltage.
May’10) (
VY20 Define power factor.
(May’12)
VY21 In a 3Φ balanced delta system, the voltage across R and Y is
400<0V. What will be the voltage across Y and B? Assume RYB (May’11)
phase sequence.
VY22 Calculate PF if v(t)=Vmsin(wt) and i(t)=Im sin(wt-45) (May’11)
VY23 In a circuit shown below, find the total power consumed by the 3Φ
load.
VX12 Write the relation between phase voltage and line voltage in
star connected system.
( May’11)
VX13 Write the condition for balanced star connected load.
( May’10)
VX14 What is meant by phase sequence?
( Nov’10)
VX15 When the load is balanced, what is the amount of current in the
neutral wire for a 3Φ 4 wire systems?
Nov/Dec (
14)
VX16 Draw the circuit diagram for balanced delta connected load.
( May’09)
VX17 What are the four methods can be analyzed in unbalanced star
connected load.
( Nov’09)
VX18 Write the relation between phase voltage and line voltage in
delta connected system.
( May’10)
VX19 Distinguish between unbalanced source & unbalanced load April/May 15
components?
May’11) (
VX11 The two line currents taken by an unbalanced delta connected
load are ( Nov’10)
VY29 Write the distortion power factor equation of 3Ф circuits April/May 15
VY30 Write the effect of power factor in energy consumption billing May/June 14
PART B
VX2 (i) What are the advantages of 3-phase systems? 6 (May’13,Nov’13)
VX1 (i) Prove that the total instantaneous power in a balanced three 8
(May’13) phase system is constant and is equal to the average power
whether the load is star or delta connected.
(ii) An unbalanced star connected load has balanced voltages of
8 100V and RBY phase sequence. Calculate the line
currents and the neutral current. Take ZA=15Q, ZB=(10+jfi)Q,
Zc=(6-j8)Q.
May’10) (
VY24 A 3Φ Motor can be regarded as a balanced star load.
A 3Φ motor drawn 5.6 KW when the line voltage is 220V and the line current is 18.2A. Determine the PF of the motor.
( Nov’12)
VY25 In the measurement of three phase power using two wattmeter
method , when both the wattmeter read same values, what is the value of power factor of the load?
Nov’11) (
VY26 A balanced star connected load of (3 - j4Ω) impendance is
connected to 400 V,3Φ supply. What is the real power consumed?
( May’09)
VY27 A symmetrical three phase, 400 V system supplies a balanced
mesh connected load. The current in each branch circuit is 20A
and the phase angle is 40 degree lag. Fine (a) the line current ( b) the total power.
( Nov’09)
VY28 Write the expression for three phase total power.
( Nov/Dec 2014)
VX3 (i) An unbalanced star connected load is supplied from a 8 (May’10) 3Φ 440V, symmentrical system. Determine the line currents and the power input to the circuit shown in fig. Assume RYB
sequence. Take phase voltage VRB as reference in the supply
VY6 (i) If W1 and W2 are the readings of the 2 wattmeter’s which 8
(May’12) measures power in the three phase balanced system and if
W1/W2=a, shows that the power factor is cos(Ф)=(a+1)/Sqrt(a^2-a+1).
(ii) Obtain the readings of two wattmeters connected to a 3Φ 3
8 wire 120V system feeding a balanced delta
connected load impedance of 12<30 W. Assume either phase
sequence. Find the phase power and compare the total power to
the sum of the wattmeter readings.
side.
( ii) A 3Φ, 3 wire 120V RYB system feeds a delta connected load
whose phase impedance is 30<45 Ω. Find the phase and line currents in this system and draw the phasor diagram.
8
VY5 ( i) A 3Φ balanced delta - connected load of (4+j8) Ω is connected across a 400 V,3Φ supply. Determine the phase currents and line currents. Assume the RYB phase sequence. Also calculates the power drawn by the load.
8 ( May’12)
( ii) The 2 wattmeter method produces wattmeter readings
P1=1560 W and P2=2100 W when connected to a delta connected load. If the line voltage is 220 V. Calculate (a) the Per - phase average power (b) the per - phase reactive power (c power factor (d) Phase impedance. )
8
VY7 (i) 2 wattmeter’s are connected to measure the power in a 3Ф 3 8
(May’10) wire balanced load. Determine the total power and power factor
if the 2 wattmeter’s reading (a) 1000W each both Positive. (b) 1000W each of
opposite sign.
VY7 ( ii) For the circuit shown below, calculate the line current, the 8 ( Nov’12) power and the PF. The values of R, L and C in each phase are 10 Ω, 1H and 100uF respectively.
VY9 ( i) A 3Ф 400 Volts supply is given to a balanced star connected load of impedance 8+j6 Ωs in each branch. Find the line current, power factor and total power.
8 Nov/Dec 2014) (
VY9 ii) ( impedances Z 1=( 3 17.32+j10) , Z2=(20+j34.64) and Z 3=(0 -
j10) Ωs are delta connected to a 400V, three Phase system. Determine the phase currents, line currents and total power consumed by the load.
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VX2 ( ii) Determine the line currents for the unbalanced delta
connected load shown below, phase sequence is RYB.
10 ( May’13,Nov’13)
VX4 Explain the behaviour of unbalanced loads in 3phase system. 16 (Nov’13)
VY8 Explain power and power factor measurements in three phase 16 (Nov/Dec 2014) circuits by
two wattmeter method.
