1
Code No: R7100206
I B.Tech (R07) Regular & Supplementary Examinations, June 2009 ELECTRICAL CIRCUIT ANALYSIS (Electrical & Electronics Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Four resistors are in parallel. The current in the first three resistors are 4A, 5A and 6A respectively. The voltage drop across the fourth resistor is 200V. The total power dissipated is 5KW. Determine the values of resistances of the branches and the total resistance. (b) A coil of 5Ω resistance is connected in parallel with a coil of R1 Ω resistance. This combination is then connected in series with an unknown resistor R2 Ω and the complete circuit is then connected to a 50V d.c supply. Calculate the value of R1 and R2 if the power dissipated by the resistor R2 is 150W with 5A passing through it. [6+10] 2. (a) Derive an expression for the energy stored in an inductor and a capacitor. (b) Obtain an expression for Co-efficient of coupling.
[10+6]
3. (a) Compare series and parallel resonant circuits. (b) A series RLC circuit consists of resistor of 100 Ω, an inductor of 0.318H and a capacitor of unknown value. When this circuit is energised by a 230V, 50Hz ac supply, the current was found to be 23A. Find the value of capacitor and the total power consumed. [4+12] 4. (a) Three identical impedances of (3+j4)Ω are connected in delta. Find an equivalent star network such that the line current is the same when connected to the same supply. (b) Three impedances of (7+j4)Ω, (3+j2)Ω and (9+j2)Ω are connected between neutral and the R, Y and B phases. The line voltage is 440V, calculate. i. The line currents and ii. The current in the neutral wire. iii. Find the power consumed in each phase and the total power drawn by the circuit. [4+12] 5. (a) What is complete incidence matrix? How is reduced incident matrix obtained from it? Explain with suitable example. (b) Explain network analysis using network topology based on KVL and KCL. [8+8] 6. (a) State and explain Maximum Power Transfer Theorem. (b) State Millmann’s Theorem and Tellegon’s Theorem.
[10+6]
7. Derive an expression for the current response in R-L series circuit with a sinusoidal source.[16] 8. Give the expression for Y parameters and derive the relationship between them and z and transmission parameters. [4+6+6] ?????
2
Code No: R7100206
I B.Tech (R07) Regular & Supplementary Examinations, June 2009 ELECTRICAL CIRCUIT ANALYSIS (Electrical & Electronics Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) Find the current through 25 ohms resistance using source transformations. (b) Discuss how the voltage and current sources can be converted vice-versa with suitable examples. [8+8] 2. An iron ring of cross sectional area 800 mm2 and of mean radius 170mm has two windings connected in series, one of 500 turns and the other of 700 turns. If the relative permeability of iron is 1200 find , (a) The self inductance of each coil. (b) The mutual inductance, assume that there is no leakage. Derive the formulae used. [16] 3. Two impedances Z1 =10+j31.4 Ω and Z2 =(10+R)+j(31.4-Xc) are connected in parallel across a single phase ac supply. The current taken by the two impedance branches are equal in magnitude and the phase angle between them is 900 . Calculate the values of R and Xc and the phase difference of the branch currents with respect to the applied voltage. [16] 4. (a) Three identical impedances of (3+j4)Ω are connected in delta. Find an equivalent star network such that the line current is the same when connected to the same supply. (b) Three impedances of (7+j4)Ω, (3+j2)Ω and (9+j2)Ω are connected between neutral and the R, Y and B phases. The line voltage is 440V, calculate. i. The line currents and ii. The current in the neutral wire. iii. Find the power consumed in each phase and the total power drawn by the circuit. [4+12] 5. (a) Deduce the relationship between the phase and line voltages in a star connected circuit. (b) Three similar inductive coils, each having a resistance of 20Ω and reactance of 12.57Ω are connected in star are fed from a 3-phase, 50Hz, 200V supply. Calculate the line current and the power absorbed. [16] 6. (a) State Thevenin’s Theorem. (b) Compare Thevenin’s Theorem with Norton’s theorem. (c) Explain the steps to apply Thevenin’s Theorem and draw the Thevenin’s equivalent circuit. [4+6+6] 7. Derive the expression for transient response of RLC series circuit with unit step input.
[16]
8. Discuss the about equivalent of a symmetric (a) T- network (b) π - network. for z and y parameters.
[8+8] ?????
3
Code No: R7100206
I B.Tech (R07) Regular & Supplementary Examinations, June 2009 ELECTRICAL CIRCUIT ANALYSIS (Electrical & Electronics Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) An electric circuit has three terminals A,B and C. Between A and B is connected a 2Ω resistor, between B and C are connected a 7Ω resistor and 5Ω resistor in parallel and between A and C is connected a 1Ω resistor. A battery of 10V is then connected between terminals A and C. Calculate, i. Total current drawn from the battery. ii. Voltage across the 2Ω resistor and iii. Current passing through 5Ω resistor. (b) Three capacitors of 5µf, 10µf and 15µf are connected in series across a 100V dc supply. After being charged, these are disconnected from the supply and then connected in parallel plates of like polarity together. Find [10+6] i. Total charge of the combination. ii. Charge on each capacitor and iii. Voltage across the parallel combination. 2. (a) Derive an expression for the energy stored in an inductor and a capacitor. (b) Obtain an expression for Co-efficient of coupling.
[10+6]
3. (a) Derive an expression for the current, impedance, average power for a series RLC circuit excited by a sinusoidally alternating voltage and also find the power factor of the circuit. Draw the phasor diagram. (b) In an ac circuit, the applied voltage is given by v=200sin314t and the current is i=20cos314t. Find the circuit constants and also the power factor of the circuit. Draw the phasor diagram. [10+6] 4. A balanced delta connected load is supplied from a symmetrical, 3-phase, 400V, 50Hz supply system. The current in each phase is 20A and lags behind its phase voltage by an angle 400 . Calculate (a) (b) (c) (d)
The line current. Total power. Also draw the phasor diagram showing the voltages and currents in the lines and the phases. and the wattmeter readings if two wattmeters are used. [16]
5. (a) Explain how power is measured is three phase delta connected load using two wattmeters. (b) A balanced mesh connected load of (8+j6)Ω per phase is connected to a 3-phase, 50Hz, 230V supply. Calculate i. line current. ii. Power factor. iii. Reactive volt-ampere and iv. Total volt-ampere. [8+8] 6. (a) State Thevenin’s Theorem. (b) Compare Thevenin’s Theorem with Norton’s theorem. (c) Explain the steps to apply Thevenin’s Theorem and draw the Thevenin’s equivalent circuit. [4+6+6] 7. (a) Derive the DC response of an RC circuit. (b) Derive response of R-L series circuit fed by d.c. excitation of 15V and R=5Ω, and L=1H. [8+8] 8. (a) The Z parameters of a 2 port network are Z11 =20Ω, Z22 =30Ω, Z12 =Z21 =10Ω. Find the Y parameters of the network, and hence draw the pie equivalent network. (b) Give the expression for Y parameters and h parameters and derive the relationship between them. [8+8] ?????
4
Code No: R7100206
I B.Tech (R07) Regular & Supplementary Examinations, June 2009 ELECTRICAL CIRCUIT ANALYSIS (Electrical & Electronics Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ????? 1. (a) A 100V, 60W bulb is connected in series with a 100V, 100W bulb and the combination is connected across 200V supply. Find the value of resistance that should be connected across the first bulb, so that each bulb may get the rated current at the rated voltage. (b) Two batteries A and B are joined in parallel. A resistance of 5Ω is connected in series with this combination. Battery A has an emf of 110V and an internal resistance of 0.2Ω, and the corresponding values of battery B are 100V and 0.25Ω. The above circuit is connected to 200V mains. Determine the magnitude and direction of the current in each battery and the total current taken from the supply. [6+10] 2. Two long single layer solenoids have the same length and the same number of turns but are placed co-axially one with in the other. The diameter of the inner coil is 8cm and that of the outer coil is 10cm. Calculate the co-efficient of coupling. [16] 3. Why the rms values of an alternating quantity is more important than its average value. Find the rms value of the resultant current in a conductor which carries simultaneously sinusoidal alternating current with a maximum value of 15A and direct current of 15A, by deriving necessary expressions. [16] 4. A symmetrical 3-phase, 3-wire, 440V supply is connected to a star connected load. The impedances in each branch are : Z1 =(2+j3)Ω, Z2 =(1-j2)Ω, Z3 =(3+j4)Ω. Find its equivalent delta connected load. Hence find the phase and line currents and the total power consumed in the circuits. [16] 5. (a) What is complete incidence matrix? How is reduced incident matrix obtained from it? Explain with suitable example. (b) Explain network analysis using network topology based on KVL and KCL. [8+8] 6. (a) State and explain Maximum Power Transfer Theorem. (b) State Millmann’s Theorem and Tellegon’s Theorem.
[10+6]
7. A resistance of 2ohms and a capacitor of 1 F are in series. An alternating voltage V(t) = 2 sin (t + φ) is supplying suddenly. Find an expression for the voltage across the capacitor. [16] 8. Discuss the about equivalent of a symmetric (a) T- network (b) π - network. for z and y parameters.
[8+8] ?????