St.MARTIN’S ENGINEERING COLLEGE Dhulapally, Secunderabad-500 014

Subject: Network Theory Class : EEE-II

Group - A (Short Answer Questions)

UNIT-I

1 What are the advantages of a poly phase system over a single phase system

2

Derive the relationship between line and phase quantities in a 3-phaseStar

Star connected system

connected system

balanced,

i) Star connected system

3

Derive the relationship between line and phase quantities in a 3-phase Delta

connected system for balanced delta system

4

Three identical impedances of (3+j4) ohm are connected in delta. Find an equivalent

star network such that the line current is the same when connected to the the same

supply

5

Derive the expressions for wattmeter readings in two wattmeter method with balanced

star connected load connected load

6

On a symmetrical 3-phase system, phase sequence RYB, a capacitive reactance

of 8 is across YB and a coil (R+jX) cross RY. Find R and X such that Iy =0

7 Derive the formula for power factor in two wattmeter method

8

Three identical resistances are connected in a star fashion against a balanced three phase voltage supply. If one of the resistances is removed, how much power is to be reduced?

9 Explain the effect of power factor on wattmeter readings in two wattmeter method.

10 Explain how reactive power can be measured in three phase circuits

11 Three identical impedances of (10+j4) ohm are connected in star. Find equivalent delta circuit

12 Explain how three phase emfs can be generated

13 What are the possible numbers of phase sequence. Explain

14

A symmetrical 3 phase , three wire 440V supply is connected to a Y connected load and the impedance of each branch are 2 + j3 ohms. Obtain the line currents and phase currents across the load

UNIT-II

1 Explain why the current in a pure inductance cannot change in zero time.

2 Explain why the voltage across a capacitor cannot change instantaneously.

3

What is the significance of time constant of R-L circuit? What are the different ways of

defining time constant?

4

Derive the expression for i(t) of a R-L series circuit when DC voltage is applied to it at

t=0 by closing the switch. Draw the response curve i(t) vs t. define time constant of

R-L series circuit.

5

Derive the expression for I (t) and voltage across a capacitor Vc(t) for series R-C

circuit with D.C voltage applied to it at t=0.Explain about the time constant of R-C

circuit

6 Compare the classical and Laplace transform methods of solution of the network

7

Derive an expression for the current response in R-L series circuit with a sinusoidal

source

8 Distinguish between steady state and transient response

9

A Sinusoidal Voltage of 12 sin 8 t Volts is applied at t = 0 to a RC series of R= 4Ω and

c = 1 H. By Laplace transform method determine the circuit current I (t) for. Assume

zero initial condition

10 What are initial conditions? Explain the procedure to evaluate initial conditions

11 Transient response occrs in which type of circuits? Explain

UNIT-III

1

What is a pole-zero plots? What is its significance? Explain time domain behavior from

pole zero plot.

2 Define and explain the following : port, driving point functions And Transfer functions.

3 What is a transfer function? Explain the necessary conditions for transfer functions

4

What is a driving point function? Explain the necessary conditions for driving point

functions

5 According to Routh Criteria when a network is said to be stable?

6

The Laplace transform of a voltage v(t) is V(s)=4(s+1)/(s+2)(s+3). Draw poles and

zeros of this function and determine v(t) using pole-zero plot

7

The transform voltage V(s) of a network is given by V(s) =4s/(s+2)(s2+2s+2) plot its

pole-zero diagram and hence obtain v(t)

8

Find the stability of the network

Q(S) =40S/S3 +2S2+8S+1

9

Find Y parameters for the above network shown in Figure

10

For the given network function draw pole zero diagram and hence obtain the time

domain response i(t) if I(s) = 5S / (S+1)(s2+4S+8)

UNIT-IV

1 Define active and passive ports

2 Why Z-parameters are called as open circuit impedance (Z) parameter

3 Define open circuit forward transfer impedance

4 Give the condition for reciprocity for Z parameters

5 Why Y parameters are called as short circuit admittance Parameters

6 What are the applications of cascaded ABCD parameters

7 Express y-parameters in terms of h-parameters

8 Express Z-parameters in terms of h-parameters

9

1) A two port n/w has the following Z - parameters Z11 = 40 ohm, Z22 = 30, Z12 =

Z21 = 20. Compute the transmission parameters for the n/w. Hence write the n/w

equations with the use of the parameters

10 Express Z parameters in terms of ABCD parameters

11 Express h-parameters in terms of ABCD parameters

12

Find the transmission parameters of the network shown in figure below.

UNIT-V

1 Define a filter and What are the classification of filters

2 Explain the formula for characteristic impedance of symmetrical T-Section

3

Explain the design procedure for a constant K low pass filter and its

characteristics

4

Find the component values of a constant K. LPF having characteristic impedance Z0 = 500Ω and cut off frequency of ‘fc’= 500 Hz. Find the frequency at which this filter produces an alternation constant of 38.2 dB

5 Write short note on m-derived filters

6 Design a constant K band elimination filter with cut off frequency 1750 Hz to 4250 Hz and a characteristic impedance of 250Ω

7 Write short notes on Fourier transform theorems.

8 Write short notes on Exponential form of Fourier series

9 Write short notes on Line and phase angle spectra

10 Write short notes on Fourier integrals

11 Design a Band elimination filter having a design impedance of 500 ohms and cut-off frequencies f1=1 KHz, f2=5 KHz?

12 Explain about Band Pass Filter

13 Explain the characteristics of an ideal filter

Group -B (Long Answer Questions)

UNIT-I

1

A three phase balanced delta connected load of (10+j8) ohm is connected across a 400V, 3-Ø balanced supply. Determine the phase currents and line currents. Assume the phase of sequence to be RYB. Also calculate the power drawn by load

2 Three impedance each 5 +j12 ohm is connected in star are connected to a 220 V three phase, 50 HZ supply. Calculate the line currents and the power drawn by the circuit

3

A three phase balanced delta connected load of (4+j8) ohm is connected across a400V, 3-Ø balanced supply. Determine the phase currents and line currents. Assume the phase of sequence to be RYB. Also calculate the power drawn by load.

4

A balanced 3-phase star connected load of 200 kW takes a leading current of 150 amps with a line voltage of 1200 V at 50 Hz. What are the circuit constants of the load per phase?

5

The two watt meter readings in a 3 - phase power measurement are 800 W and 400 W. The latter reading is being obtained after the reversal of current coil. Calculate the total power and power factor of the load

6

A 3-phase 500 V motor operates at a power factor of 0.4 and takes an input power of 30 kW. Two watt meters are employed to measure the input power. Find readings on each instrument.

7

A balanced three phase is connected to balanced 3 - phase power system. The line voltage is 480 volts and the line current is 10 A. the angle of the phase impedance of the load 60. Find the complex power and real power absorbed by the load.

8

Two wattmeters are used to measure power in a 3-phase three wire load. Determine the total power, power factor and reactive power, if the two wattmeter’s read i) 1000W each, both positive ii) 1000W each, but of opposite sign.

9

Three star connected impedances 5030, 4060, 4060 ohms are connected to a 400V, 3-Phase supply. Determine the line currents and the two watt meter readings when power is measured by 2 watt meter method and abc is the phase sequence.

10 A star connected load of Z = 6Ω, Z = j5Ω, Z = j7Ω is supplied by a 400V, R Y B 3- Ø symmetrical supply. Determine the line currents. The phase sequence is RYB.

UNIT-II

1

For the circuit shown in Figure determine the particular solution for i(t) through the

circuit. Assume zero initial conditions

2

Derive an expression for the response in the system in Figure.2 By time domain and

Laplace transform techniques. Cross Check the answer. V (t) = 5(Sin1000t+π/6).

3

For the circuit given in Figure steady state conditions are reached for the switch K in

position ‘1’. At t = 0, the switch is changed to position 2. Use the time domain

method to determine the current through the inductor for all t≥0.

4

A dc voltage of 100V is applied in the circuit shown in figure a and the switch is kept

open. The switch K is closed at t = 0. Find the complete expression for the current

5

For the circuit shown in Figure determine the particular solution for i(t) through the

circuit. Assume zero initial conditions

6

A series RL circuit with R = 50 ohms and L = 0.2 H has a sinusoidal voltage source V

= 150 (500Sint φ+ volts applied at a time when φ=0. Find the expression for the

total current. Use Laplace transforms method.

7 A series R C circuit with R = 100 Ω and C = 25 μF has a Sinusoidal excitation V (t) = 250 Sin 500t. Find the total current assuming that the capacitor is initially uncharged

8

A series RC circuit with R = 50 ohms and C = 2 micro farad has a sinusoidal voltage source V = 150 (500Sint φ+π/3) volts applied at a time when φ=0. Find the expression for the total current. Use Laplace transforms method

9 A dc voltage of 20V is applied in a RL circuit where R = 5 And L = 10H. Find i. The time constant ii. The maximum value of stored energy

10

A Sinusoidal Voltage of 12 sin 8 t Volts is applied at t = 0 to a RC series of R= 4Ω and L = 1 H. By Laplace transform method determine the circuit current i (t) for. Assume zero initial condition

UNIT-III

1

Find the transfer function V2(S)/V1(S) for the circuit in the figure

2

For the following network shown in figure determine Z parameters

3

Find the transfer function V2(S)/V1(S)for the circuit in Figure

4

Draw the transformed circuit for given circuit and obtain i(t)

5

For the two port network shown in the Figure find G12[V2(S)/V1(S)]

6

For the circuit shown in the Figure.3, find i(t). Assume zero initial conditions Use

Laplace transforms approach. The switch is closed at t = 0.

7

Find Y12 for the circuit in Figure

8

For the network shown in the figure below determine the transfer functions G21 (S)

And Z21(S). Also find Z11(S)

9

Find Z parameters for the network shown in Figure

UNIT-IV

1

Obtain Z-parameters of the two port network

2

Find the Z parameters of the circuit shown

3

Determine the ABCD parameters of two networks connected in cascade as shown in

figure

4

Find the h-parameters for the circuit in figure

5

Find the Y-parameters of the network shown

6

Determine the ABCD parameters of two networks connected in cascade as shown

7

The Z parameters of a two port network are Z11=6Ω, Z22=4Ω, Z12=Z21= 3Ω

Compute Y and ABCD Parameters and write the describing equations

8 Discuss in detail about series and parallel connection of two port networks

9

For the two port network given below (Shown in Figure.3) determine ABCD & hybrid

parameters

10

For the two port network given below (shown in Figure.4) determine Y and ABCD

parameters

UNIT-V

1 Design a low pass filter (both T and π sections) having a cutoff frequency of 2 KHz to operate with a terminated load resistance of 500Ω

2 Design a symmetrical T-attenuation to give 20 dB attenuation and to have characteristic impedance of 300Ω

3 Design a symmetrical T attenuator to give 2 dB attenuation to have a characteristic impedance of 150Ω

4 Draw the circuit diagram of a Band pass filter. Explain the design procedure of the above filter in detail

5 Draw the circuit diagram of a High pass filter. Explain the design procedure of the above filter in detail

6 Draw the circuit diagram of a Low pass filter. Explain the design procedure of the above filter in detail

7

Design a proto type section of band pass filter having cut-off frequencies of 12KHz

and,16 KHz and a design impedance of 600 ohm

8

Find the trigonometric Fourier series for the wave shown in fig. and plot the spectrum

9

Find the exponential Fourier series for the waveform shown in figure

10

Find the exponential Fourier series for the waveform shown in fig and plot the spectrum

Group – C Analytical

UNIT-I

1

A r.m.s voltage in a three phase star circuit is given by 231V (ph. –N). Write the instantaneous voltage expression. If the current in each phase lag the corresponding phase voltages by 30ᵒ what are the expressions of instantaneous currents?

2

A Three phase 4 wire 100 V (L-L) system supplied a balanced Y connected load having impedances of 10 - 30ᵒΩ in each phase. Find line currents and draw the phasor diagram. How much current is flowing through the neutral

3

A ∆ connected load half a parallel combination of resistance (5 Ω) in each phase. If a balanced 3 phase 400 V supply is applied between lines, find the phase currents and line currents and draw the phasor diagram.

4

A 3 phase, star connected system with 400 V (L-L) is disconnected to three loads: 25 0ᵒ , 11 - 20ᵒ ohm (also connected in star). Find the line current, power and the current in the neutral of the system.

5

A three phase Y connected load has an inductor of 500 mH and capacitance of 100 µF in each phase. The load is connected across a 100V, 50Hz three phase balanced system Find the line currents for the load.

6

The power in a three phase circuits is measured by two wattmeters. If the total power is d50kW, power factor being 0.8 leading, what will be the reading of each wattmeter? For what plf. Will one of the wattmeter’s read zero?

7 A three phase 400 V, 50Hz, 25 HP motorist delta connected and is operating at 0.85 lag and efficiency of 80% What is the line current?

8

A three phase induction motor takes 100 kVA at 0.6 p.f. (lag) from a 440 V three phase 50 Hz source (balanced). There is another load on the same line and the load is connected in form of a ∆ having 8 Ω resistance and – j 24 Ω reactance in series in each phase. Find the total VA power, average power, reactive power. Line current and the p.f. of the combination.

9

A balanced Y connected 3 phase load has an impedance of Zph(=5-j 4) ohms in each phase. Find the line currents if a balanced 3 ph source of 100 V are applied across it. Draw the phasor diagdram?

UNIT-II

1

What is mean by steady state condition? A dc voltage of 100V is applied in the circuit shown in figure a and the switch is kept open. The switch K is closed at t = 0. Find the complete expression for the current

2

A dc voltage of 20V is applied in a RL circuit where R = 5 and L = 10H. Find i. The time constant ii. The maximum value of stored energy.

3

Find i (t) in the circuit for the following figure Use Laplace method

4

Find I c (t) at t = 0 + while the switching is done from x to y at t = 0. As shown in

figure.

5 Define 1) Delay time 2) Peak over shoot 3) Settling time

6

A DC voltage of 20V is applied in a R-L circuit where R=5_ and L=10H. Find the i) Time constant ii) The maximum value of stored energy

7

A series R-L circuit with R=100_, L=1H has a sinusoidal voltage source 200sin (500t+¢) applied at time when¢=0. Find i) The expression for current ii) At what value of ¢ must the switch be closed so that the current directly enter steady state

8 A series RC circuit, with R=50_, C=10μF has a sinusoidal voltage 230_2sin (2_x50t). Find the transient response

9 A series R-L circuit with R=50_ and L=0.2H, has a sinusoidal voltage source V=150sin (500t+¢)V applied at time when¢=0. Find the complete current

10 A series RLC circuit with R=5_, L=0.1H, C=500μF has a sinusoidal voltage v=100sin(250t+¢) volts applied at time when¢=0. Find the resulting current

UNIT-III

1

Find the transfer function V2(S)/V1(S) for the circuit in the figure

2

For the following network shown in figure determine Y parameters

3

For the circuit given below determine current supplied by the source, total active &

reactive powers also draw the phasor diagram.

4

For the network shown in the figure below determine the Y parameters

5

Find Z parameters for the network shown in Figure

6

Find the transfer function V2(S)/V1(S)for the circuit in Figure

7

Draw the transformed circuit for given circuit and obtain i(t) at time t=0

8

For the two port network shown in the Figure find impedance parameters

9

For the circuit shown in the Figure.3, find i(t). Assume zero initial conditions. Use

Laplace transforms approach. The switch is closed at t = 0.

10

Find Z parameters for the circuit in Figure

UNIT-IV

1 In a T network Z1 = 2_ 0o, Z2 = 5 _− 90o, Z3 = 3_ 90o, find the Z- parameters

2 Z-parameters for a two port network are given as Z11=25, Z12=Z21=20, Z22=50. Find the equivalent T-network.

3

Find the Z-parameters in the above circuit

4

Find the Z-parameters in the circuit

5 Two two-port networks a and b with transmission parameters Ta and Tb are connected in cascade. Obtain Z parameters of the combination

6

Find the Z-parameters of the two-port circuit of Fig.

7 Derive the formulas for image impedance of two port networks.

8 Obtain Y parameters in terms of transmission parameters.

9 What is the condition of reciprocity and symmetry for H parameters?

10 What is the condition of reciprocity and symmetry for ABCD parameters?

UNIT-V

1 Design a low pass T and _ section filters having a design impedance R0=600 and cut-off frequency =2000Hz

2 Design a proto type section of band pass filter having cut-off frequencies of 1 KHz and, 5 KHz and a design impedance of 600Ω_?

3 Design a proto type section of band pass filter having cut-off frequencies of 12KHz and,16 KHz and a design impedance of 600 ohm?

4

A constant K low pass filter is designed to cut-off at a frequency of 1000Hz and the resistance of the load circuit is 50ohm. Calculate the values of the corresponding components required.

5 Design a constant k-high pass filter to have a cut-off frequency of 2 KHz and a design impedance of 100ohm

6 Design a constant k filter to eliminate band of frequencies lying between 2000Hz and 5000Hz with a design impedance of 600ohm

7 Design a band pass filter with cut off frequencies of 2000Hz and 5000Hz and a design impedance of 500ohm

8 Design a constant k high pass filter to cut off at 10KHz and design impedance of 600ohm

9

Find the trigonometric Fourier series for the triangular wave shown in fig. and plot the

spectrum

10 What are the properties of Fourier series

11 Design a low pass T and _ section filters having a design impedance R0=600_ and cut-off frequency =2000Hz