ee6201 circuit question bank

8/12/2019 Ee6201 Circuit Question Bank

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BASIC CIRCUIT ANALYSIS

UNIT-I

PART-A

1. What is a graph of network?

When all elements in a network are replaced by lines with circles of dos at both ends.

2. What is tree of a network?

It is an interconnected open set of branches which include all the nodes of the givengraph.

3. Give the properties of tree in a graph.

It consists of all the nodes of the graph

If the graph has N no of nodes the tree will have N-I branches

There will be no closed path in the tree

There can be many possible different trees for a given graph depending on the noof nodes and branches.

4. Define Ohms Law.

The potential difference across any two ends of a conductor is directly proportional to thecurrent flowing between the two ends provided the temperature of the conductor remainsconstant.

5. Define Quality factor.

The quality factor is defined as the ratio of maximum energy stored to the energydissipated in one period.

6. What are half power frequencies?

In RLC circuits the frequ ncies at which the power is half the max/min power arecalled half power frequencies.

7. Define selectivity.

It is defined as the ratio of bandwidth and resonant frequency. 1


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8. Write the characteristics of series resonance.

At resonance impedance in min and equal to resistance therefore current is max. Before

resonant frequency the circuit behaves as capacitive circuit and above resonant frequencythe circuit will behave as inductive circuit. At resonance the magnitude of voltage across

the inductance and capacitance will be Q times the supply voltage but they are in phase

opposition.

9. What is anti resonance?

In RLC parallel circuit the current is min at resonance whereas in series resonancethe current is max. Therefore the parallel resonance is called anti resonance.

10. Write the characteristics of parallel resonance.

At resonance admittance in min and equal to conductance therefore the current ismin.

Below resonant frequency the circuits behave as inductive circuit and above resonantfrequency the circuit behaves as capacitive circuit.

At resonance the magnitude of current through inductance and capacitance will beq times the current supplied by the source but they are in phase opposition.

11. Define KCL

KCL states that the algebraic sum of currents in node is zero.

12. Define KVL

KVL states that the algebraic sum of voltages in a closed path is zero.

13. What is meant by linear and nonlinear elements?

Linear element shows the linear characteristics of voltage Vs current.

Nonlinear element the current passing through it does not change linearity with the

linear change in applied voltage at a particular frequency.

14. What is meant by active and passive elements?

If a circuit element has the capability of enhancing the energy level of a signalpassing through it is called an active element.

Passive elements do not have any intrinsic means of signal boosting.


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15. What is meant by unilateral and bilateral elements?

If the magnitude of the current passing through an element is affected due to changein the polarity of the applied voltage is called unilateral elements.

If the current magnitude remains the same even if the applied EMFs polarity ischanged is called bilateral elements.

16. What is a dual network?

In an electrical circuit itself there are pairs of terms, which can be interchanged toget new circuits. Such pair of dual terms is given below

Current- Voltage

Open- Short

L-C

R-G

Series Parallel

Voltage source- Current source

KCL-KVL

17. Give the steps to draw a Dual Network

In each loop of a network place a node

Draw the lines connecting adjacent nodes passing through each element and also to thereference node.

18. Mention the disadvantages of Ohms Law.

It does not apply to all non metallic conductors

It also does not apply to non linear devices such as zener diode, vacuum tubes etc.

It is true for metal conductors at constant temperature. If the temperature changesthe law is not applicable.

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19. Compare series and parallel circuit.

S Series circuit Parallel circuitNo

1

The total effective resistance is the sum of theindividual resistance ie

Reff=R1+R2+R n

The reciprocal of the total effectiveresistance is the sum of the reciprocals ofindividual resistance

1/Reff= 1/R1+1/R2+.1/R n

2 Only one path for the current flow

3 The current flowing through all theresistances will be the same and equal to thetotal current

4 The voltage is divided across each resistanceaccording to the value of resistance.

More than one path for the current toflow

The current flowing through eachresistance is different

The voltage across each resistance issame which will be equal to the inputvoltage.

20. What is a node?

A node is a point in a network in which two or more elements have acommon connection.

21. What are the classificatio ns of Circuit elements?

Active element

Passive element

Lumped and distributed elements

Bilateral and unilateral elements

Linear and non linear elements.

22. What are dependent and independent sources?

The electrical energy supplied by dependent sources a source of electrical energy.

The electrical energy supplied by independent source does not depend on anotherelectrical source. They convert some energy in to electrical form.

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23. Define series and parallel connection.

If the resistances are connected end to end the combination is said to be series.

24. What is a super node?

The region surrounding a voltage source which connects the two nodes directlycalled super node.

25. What is principle node?

The meeting point of three or more elements is called principle node.

26. What is a closed path?

A closed path which starts at a node and travels through some part of the circuit andarrives at the same node without crossing the node or more than once.

27. State voltage division rule.

Voltage across a resistor in series circuit is equal to the total voltage across the serieselements multiplied by the value of that resistor divided by the total resistance of the serieselements.

28. State current division rule.

The current in any branch is equal to the ratio of the opposite parallel branchresistances to the total resistance value, multiplied by the total current in the circuit.

29. Define mesh.

A mesh is defined as a lo op which does not contain any other loops within it.

30. What is a planar circuit?

A circuit is said to be non planar if it cannot be drawn on a plane surface withoutcrossovers.

31. Define super mesh.

The loop existing around a current source which is common to the two loops is calledsuper mesh.

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PART-B

1. Find the current through each branch by network reduction technique.

2. Calculate a) the equivalent resistances across the terminals of the supply, b) totalcurrent supplied by the source and c) power delivered to 16 ohm resistor in the circuitshown in figure.

3. In the circuit shown, determine the current through the 2 ohm resistor and thetotal current delivered by the battery. Use Kirchhoffs laws.

4. (i) Determine the current through 800 ohm resistor in the network shown in figure. (8)

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(ii) Find the power dissipated in 10 ohm resistor for the circuit shown in figure. (8)

5. (i) In the network shown below, find the current delivered by the battery. (10)

(ii) Discuss about voltage and current division principles.

(6) 6. (i) Explain :Kirchoff laws. (4)Dependent sources (2)Source transformations

(2) with relevantdiagrams.

Voltage division and current division rule (4)(ii) Calculate the resistance between the terminals AB. (4)

7. i)Determine the value of V2 such that the current through the impedance(3+j4) ohm is zero.

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ii) Find the current through branch a-b using mesh analysis shown in figure below.

8. Determine the mesh currents I1 and I2 for the given circuit shown below

9.Find the node voltages V1 and V2 and also the current supplied by the source forthe circuit shown below.

10.Find the nodal voltages in the circuit of figure.

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11. i) Using the node voltage analysis, find all the node voltages and currents in 1/3ohm and 1/5 ohm resistances of figure.

ii) For the mesh-current analysis, explain the rules for constructing meshimpedance matrix and solving the matrix equation [Z]I = V.

12. Solve for V1 and V2 using nodal method. Let V = 100V.

13. Using Mesh analysis, find current through 4 ohm resistor.

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14.Use nodal voltage method to find the voltages of nodes m and nand currents through j2 ohm andj2 ohm reactance in the networkshown below.

15.For the circuit shown find the current I flowing through 2 ohm resistance usingloop analysis.

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8. State Tellegens theorem.

It states that the summation of all the product of branch voltage and its current ofa circuit is zero.

9.State the steps to solve the super position theorem.Take only one independent voltage or current source

Obtain the branch currents

Repeat the above for ther sources

To determine the net ranch current just adds the currents obtained above.

10.State the steps to solve the Thevenins theorem.Remove the load resistance and find the open circuit voltage VOC

Deactivate the consta t sources (fro voltage source remove it by internalresistance & for current source delete the source by OC) and find the internal

resistance (RTH) of the source side looking through the open circuitedload terminals

Obtain the Thevenins equivalent circuit by connecting VOC in series with RTH

Reconnect the load resistance across the load terminals.

11. State the steps to solve the Nortons theorem.

Remove the load resistor and find the internal resistance of the sourceN/W by deactivating the constant source.

Short the load terminals and find the short circuit current

Nortons equivalent circuit is drawn by keeping R TH in parallel with ISC

12. What is the Load current in a Nortons circuit?

IL= (ISC.RTH) / (RTH+RL)

13. What is the load current in Thevenins circuit? IL=

VOC/ (RTH+RL)

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14. What is the maximum power in a circuit?

Max power:VO C2

/4 RTH

15. Write some applications of maximum power transfer theorem.

Power amplifiers

Communication system

Microwave transmission

16. What is the limitation of superposition theorem?

This theorem is valid only for linear systems. This theorem can be applied forcalculating the current through or voltage across in particular element. But this

superposition theorem is not applicable for calculation of the power.

17. What are the limitations of maximum power transfer theorem?

The maximum efficiency can be obtained by using this theorem is only 50% .

It is because of 50% of the power is unnecessarily wasted in Rth.

Therefore this theorem only applicable for communication circuits and not for

power circuits where efficiency is greater importance rather than power delivered.

18. State voltgae division rule.

Voltage across a resistor in a series ciruict is equal to the total voltage across

elements mulitiplied by the value of that resistor divided by the total resistance of

the series elements.

V1=(R1)*V/ (R1+R2)

19. State current division rule.

Current in any branch is equal to the ratio of the opposite paralel branch resistance to

the total resistance value, multiplied by the total current in the circuit.

I1=(R2)*I/(R1+R2)


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20. Define source transformtion.

The current and voltage sources may be inter changed without affecting the remainder

of the circuit, this technique is the source transformation. It is the tool for simplifying the

circuit.

21. List the applications of Thevinins theorem.

It is applied to all linear circuits including electronic circuits represented by the

controlled source.

This theorem is useful when t is desired to know the effect of the response in network or

varying part of the network.

22. Explain the purpose of star delta transformation.

The transformation of a given set of resistances in star to delta or vice versa

proves extremely useful in circuit analysis and the apparent complexity of a

given circuit can sometime by very much reduced.

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PARTB

1. (i) Find the value of R and the current flowing through it in the circuit shown whenthe current in the branch OA is zero. (8)

ii) Determine the Thevenins equivalent for the figure (8)

2.Derive expressions for star connected arms in terms of delta connected arms and deltaconnected arms in terms of star connected arms. (16)

3. Determine Thevenins equivalent across the terminals AB for the circuit shown in figurebelow. (16)

4. Find the Thevenins s equivalent circuit of the circuit shown below, to left of the terminals ab.

Then find the current through RL = 16 ohm and 36 ohm. (16)

5. i) Find the current through branch a-b network using Thevenins theorem. (8)

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ii) Find the current in each resistor using superposition principle of figure. (8)

6. i) Determine the Thevenins equivalent circuit. (8)

(ii) Determine the equivalent resistance across AB of the circuit shown in the figure below.(8)

7. For the circuit shown, use sup rposition theorem to compute current I.

8. (i)Compute the current in 23 ohm resistor using super position theorem for thecircuit shown below. (8)

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(ii) Find the equivalent resistance between B and C in figure (8)

9. Using superposition theorem calculate current through (2+j3) ohm impedance branch of thecircuit shown.

10. i) For the circuit shown, determine the current in (2+j3) ohm by usingsuperposition theorem. (8)

ii) State and prove Nortons theorem. (8)

11.i) Find the value of RL so that maximum power is delivered tothe load resistance shown in figure. (8)

ii) State and prove compensation theorem. (8)12. Determine the maximum power delivered to the load in the circuit. (16)

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13. Find the value of impedance Z so that maximum power will be transferred from source toload for the circuit shown. (16)

14. i) State and explain maximum power transfer theorem for variable Pure resistive load.(8) ii) Using Nortons theorem, find current through6 ohm resistance shown in figure.

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UNIT III

RESONANCE AND COUPLED CIRCUITS

1. What is meant by Resonance?

An A.C circuit is said to be resonance if it behaves as a purely resistive circuit. The total

current drawn by the circuit is then in phase with the applied voltage, and the power factor will

then unity. Thus at resonance the equivalent complex impedance of the circuit has no j

component.

2. Write the expression for the resonant frequency of a RLC series

circuit. Resonant frequency fr=1/2LC

3. What is resonant frequency?

The frequency at which resonance occurs is called resonant frequency.

At resonant frequency XL=XC

4. Define series resonance.

A resonance occurs in RLC series circuit called series resonance. Underresonance condition, the input current is in phase with applied voltage.

5. Define Quality factor.

The quality factor is defi ned as the ratio of maximum energy stored to the energy

dissipated in one period.

6. What are half power frequencies?

In RLC circuits the frequ ncies at which the power is half the max/min power arecalled half power frequencies.

7. Write the characteristics of series resonance.

At resonance impedance in min and equal to resistance therefore current is max.

Before resonant frequency the circuit behaves as capacitive circuit and aboveresonant frequency the circuit will behave as inductive circuit.

At resonance the magnitude of voltage across the inductance and capacitance will be Qtimes the supply voltage but they are in phase opposition.

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8. Define selectivity.

It is defined as the ratio of bandwidth and resonant frequency.

9. What is anti resonance?

In RLC parallel circuit the current is min at resonance whereas in series resonancethe current is max. Therefore the parallel resonance is called anti resonance.

10. Write the characteristics of parallel resonance.

At resonance admittance in min and equal to conductance therefore the current ismin.

Below resonant frequency the circuits behave as inductive circuit and above resonantfrequency the circuit behaves as capacitive circuit.

At resonance the magnitude of current through inductance and capacitance will beq times the current supplied by the source but they are in phase opposition.

11. What is Bandwidth and sel ctivity?

The frequency band within the limits of lower and upper half frequency is calledbandwidth.

BW=f2-f1

Selectivity is the ratio of fr to the bandwidth

Selectivity= fr / (f2-f1)

12. What are coupled circuits?

It refers to circuit involving elements with magnetic coupling. If the flux produced by anelement of a circuit links other elements of the same circuit then the elements are said to bemagnetic coupling.

13. What are coupled circuits?

When two or more coils are linked by magnetic flux, then the coils arecalled coupled circuits.

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14. State the properties of a series RLC circuit.

The applied voltage and the resulting current are in phase, when also means thanthe p.f of RLC circuit is unity.

The net reactance is zero at resonance and the impedance does not have the resistivepart only.

The current in the circuit is max: and is V/R amperes

At resonance the circuit has got minimum impedance and max: curre nt

Frequency of resonance is given by fr=1/(2LC)

15. State the properties of a parallel RLC circuit.

PF is unity

Current at resonance is (V/(L/RC)) and is in phase with the appliedvoltage. The value of current at resonance is minimum.

Net impedance at resonance is max: & is equal to L/RC

The admittance is min: and the net susceptance is zero at resonance.

16. Define self inductance.

When permeability is constant the self inductance of a coil is defined as the ratio offlux linkage and current.

17. Define mutual inductance.

When permeability is constant the mutual inductance between two coupled coils is

defined as the ratio of flux linkage in one coil due to common flux and current through another

coil.

18. Define coefficient of coupling.

In coupled coils the coefficient of coupling is defined as the raction of the totalflux produced by one coil linking another coil.

19. What is DOT convention?

The sign of mutual induced emf depends on the winding sense and the current through the

coil. The winding sense is decided by the manufacturer and to inform the user about the winding

sense a dot is placed at one end of each coil. When current enter at dotted end in one coil then the

mutual induced emf in the other coil is positive at dot end.

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21. State dot rule for coupled c rcuit.

It states that in coupled coils current entering at the dotted terminal of one coil induce

an emf in second coil which is +ve at dotted terminal of second coil.

Current entering at the un dotted terminal of one coil induce an emf in secondcoil which is +ve at un dotted terminal of second coil.

22. Define coefficient of coupling.

The amount of coupling between to inductively coupled coils is expressed in terms ofthe coefficient of coupling.

K=M/L1L2

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PARTB

1. (i) Derive bandwidth for a series RLC circuit as a function of resonant frequency.(16)

2. (i) For the circuit below, find the value of so that current and source emf are

in phase. Also find the current at this frequency. (8)

(ii) Discuss the characteristics of parallel resonance of a circuit having G,L and C. 8)

3. (i) A Pure resistor, a pure capacitor and a pure inductor are connected in parallel across a 50Hzsupply, find the impedance of the circuit as seen by the supply. Also find the resonant frequency. (8)

(ii) When connected to a 230V, 50Hz single phase supply, a coil takes 10kVA and 8kVAR.

For this coil calculate resistance, inductance of coil and power consumed.(8)

4.(i) In an RLC series circuit if 1 and 2 are two frequencies at which the magnitude ofthe current is the same and if r is the resonant frequency, prove that 2 r = 12.

(ii)A series RLC circuit has Q = 75 and a pass band (between half power frequencies) of 160Hz. Calculate the resonant frequency and the upper and lower frequencies of the pass band. (8)

5. (i) Explain and derive the relationships for bandwidth and half power frequencies of RLCseries circuit. (8)

(ii) Determine the quality facto of a coil R = 10 ohm, L = 0.1H and C = 10f (8)

6. A series RLC circuit has R=20 ohm, L=0.005H and C = 0.2 x 10-6 F. It is fed from a 100Vvariable frequency source. Find i) frequency at which current is maximum ii) impedance at this

frequency and iii) voltage across inductance at this frequency.

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7.A series RLC circuit consists of R=100 ohm, L = 0.02 H and C = 0.02 microfarad. Calculatefrequency of resonance. A variable frequency sinusoidal voltage of constant RMS value of 50V

is applied to the circuit. Find the frequency at which voltage across L and C is maximum. Also

calculate voltage across L and C is maximum. Also calculate voltages across L and C at

frequency of resonance. Find maximum current in the circuit. (16)

8.In the parallel RLC circuit, calculate resonant frequency, bandwidth, Q-factor and powerdissipated at half power frequencies. (16)

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V.MOHAMED IBRAHIM AP/EEE

www.Vidyarthiplus.comwww.Vidyarthiplus.comwww.Vidyarthiplus.com


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UNIT IV

TRANSIENT RESPONSE FOR DC CIRCUITS

1. What is transient state?

If a network contains energy storage elements, with change in excitation, the current

and voltage change from one state to other state the behavior of the voltage or current when it

is changed from one state to another state is called transient state.

2. What is transient time?

The time taken for the circuit to change from one steady state to another steady

state is called transient time.

3. What is transient response?

The storage elements deliver their energy to the resistances, hence the response

changes with time, get sturated after sometime, and are referred to the transient response.

4. Define time constant of RLC circuit.

The time taken to reach 63.2% of final value in a RL circuit is called the time constant

of RL circuit.

Time constant=L/R

5. Define time constant of RC circuit.

The time to taken to reach 36.8% of initial current in an RC circuit is called the

time constant of RC circuit.

Time constant=RC

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6. What is meant by natural frequency?

If the damping is made zero then the response oscillates with natural frequency

without any opposition, such a frequency is called natural frequency of oscillations.

7. Define damping ratio.

It is the ratio orf actual resistance in the circuit to the critical resistance.

8. Write down the condition, for the response of RLC series circuit to be under

damped for step input.

The condition for the reponse of RLC series circuit to be under damped step input is

(R/2L)2

>(1/LC)

9. Write down the condition fo the response of RLC sereis circuit to be over

damped for step input.

The condition for the response of RLC series circuit to be over damped for step inputis,

(R/2L)2>(1/LC)

10. Write down the few applications of RL, RC, RLC circuits.

Coupling circuits

Phase shift circuits

Filters

Resonant circuits

AC bridge circuits

Transformers

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11. Define transient response.

The transient response is defined as the response or output of a circuit from the instant

of switching to attainment of steady state.

12. What is natural response?

The response of a circuit due to stored energy alone without external source is

called natural response or source free response.

13. What is forced response?

The response of the circuit due to the external source is called forced response.

14. Define apparent power.

The apparent power is defined as the product of magnitude of voltage and

magnitude of current.

15. What is power factor and reactive power?

The power factor is defined as the cosine of the phase difference between voltage andcurrent.

Power factor= cos

The reactive power of the circuit is defined as the sine of the phase angle.

Reactive power= sin

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PARTB

1. In the circuit of the figure shown below, find the expression for the transient current and the

initial rate of growth of the transient current (16)

2. In the circuit shown in figure, switch S is in position 1 for a long time and brought to

position 2 at time t=0. Determine the circuit current. (16)

3.A resistance R and 2 microfarad capacitor are connected in series across a 200V direct supply.Across the capacitor is a neon lamp that strikes at 120V. Calculate R to make the lamp strike 5

sec after the switch has been closed. If R = 5Megohm, how long will it take the lamp to strike?

4.A Series RLC circuits has R=50 ohm, L= 0.2H, and C = 50 microfarad. Constant voltage of100V is impressed upon the circuit at t=0. Find the expression for the transient current assuming

initially relaxed condit ons.

5.A Series RLC circuits with R=300 ohm, L=1H and C=100x10-6 F has a constant voltage of50V applied to it at t= 0. Find the maximum value of current ( Assume zero initial conditions)

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6. A step voltage V(t) = 100 u(t) is applied to a series RLC circuit with L=10H, R=2ohm and C=

5F. The initial current in the circuit is zero but there is an initial voltage of 50V on the capacitor

in a direction which opposes the applied source. Find the expression for the current in the circuit.

7.For a source free RLC series circuit, the initial voltage across C is 10V and the initial currentthrough L is zero. If L = 20mH, C=0.5 microfarad and R=100 ohm. Evaluate i(t).

8.For the circuit shown in figure, find the voltage across the resistor 0.5 ohm when the switch, S

is opened at t=0. Assume that there is no charge on the capacitor and no current in the inductor

before switching

9.In the circuit shown in figure, find the current i. Assume that initial charge across thecapacitor is zero.

10. In the circuit shown in figure, the switch is closed at time t=0. Obtain i(t). Assume

zerocurrent through inductor L and zero charge across C before closing the switch.

11. Derive an expression for current response of RLC series circuit transient. (16)

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UNIT V

THREE PHASE CIRCUITS

PART-A

1. Define line current and phase current.

The current flowing through the line is called line current

The current flowing through the phase is called phase current

2. Define line and phase voltag

The voltage between two lines is called the line voltage

The voltage between any line and the neutral point is called phase voltage.

3. Give the line and phase values in star connection

The relation between line and phase voltage in star connection is

EL=3Eph

The relation between line current and phase current in a star connection is

IL=Iph

4. Give the line and phase values in delta connection

The relation between line voltage and phase voltage in a delta connection is

EL=Eph

The relation between line current and phase current in delta connection is

IL=3Iph

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PARTB

1. With a neat circuit and phasor diagram explain the three phase power measurement by twowattmeter methods.

2. (i) A symmetrical three phase 400V system supplies a balanced delta connected load. Thecurrent in each branch circuit is 20A and phase angle 40 (lag) calculate the line current and total

power. (8)

(ii) A three phase delta connected load has Zab = (100+j0) ohms, Zbc = (-j100) ohms and Zca =

(70.7 =j70.7) ohms is connected to a balanced 3 phase 400V supply. Determine the line currents

Ia,Ib and Ic. Assume the phase sequence abc. (8)

3. (i) A balanced three phase star connected load with impedance 8+j6 ohm per phase is connected across a symmetrical 400V three phase 50Hz supply. Determine the line current,

power factor of the load and total power. (8)

(ii) An alternating current is expressed as i=14.14 sin 314t. Determine rms current, frequency

and instantaneous current hen t =0.02ms. (8)

4. (i) A balanced star connected load of 4+j3 ohm per phase is connected to a 400V, 3 phase,

50Hz supply. Find the line current, power factor, power, reactive volt ampere and total volt

ampere. (8)

(ii) A Voltage source 100V with resistance of 10 ohms and inductance 50 mH, a capacitor 50

microfarad are connected in series. Calculate the impedance when the frequency is (i) 50HZ (ii)

500Hz (iii) the power factor at 100Hz. (8)

5. (i) Three impedances Z1 = 345 ohm, Z2 = 10245 ohm, Z3 = 5-90 ohm areconnected in series. Calculate applied voltage if voltage across Z1 = 27-10 V. (8)

(ii) A delta connected load as shown in figure is connected across 3 phase 100 volt supply.

Determine all line currents. (8)

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ee6201 circuit question bank

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