Hall Ticket No Question Paper Code : AEE11T06

VARDHAMAN COLLEGE OF ENGINEERING

(AUTONOMOUS)

Affiliated to JNTUH, Hyderabad

Four Year B. Tech III Semester Tutorial Question Bank 2013 - 14

(Regulations: VCE-R11)

PRINCIPLES OF ELECTRICAL ENGINEERING (Electronics and Communication Engineering)

PART-A

Unit-I

1. State Tellegan’s theorem.

2. State superposition theorem

3. State reciprocity theorem

4. State Thevenin’s theorem

5. State Norton’s theorem.

6. State Millman’s theorem

7. State maximum power transfer theorem

8. What is linear, dependent source?

9. What are the limitations of superposition theorem?

10. What is the expression for the maximum power transferred when the load is resistive and the

internal resistance of the source is also resistive?

Unit-II

1. What is transient time?

2. What is initial condition?

3. What is steady state condition?

4. Reasons for evaluating initial conditions?

5. State initial value theorem

6. State final value theorem

7. Verify initial value theorem for the function given f(t)=5sin3t

8. Verify final value theorem for the function given f(t)=5-e-3t

9. Draw the basic signals representations

10. State convolution theorem

Unit-III

1. Why does the dc motor draw a very high current at starting, when started directly on lines?

2. Draw the following in respect of D.C.series motor?

(a)Torque vs speed characteristics

(b) Torque vs armature current characteristics

3. What is back e.m.f?Explain its significance

4. How can you control the speed of a dc motor for less than rated value?

5. Name and explain the type of dc motor, in which the torque developed is directly proportional to the

current drawn by the armature winding?

6. Explain the term ‘critical resistance’ of a dc shunt generator with reference to its relevant

characteristics

7. A dc generator fails to build up voltage when it is run at rated speed. What may be the possible

reasons?

8. What is residual magnetism in a dc generator?

9. A dc long-shunt compound generator delivers a load current of 50A at 500V,and has armature, series

field and shunt field resistances of 0.05Ω,0.03Ω and 250Ω,respectively.Calculate the generated emf

and the armature current, allow 1V per brush for contact drop

10. What is the purpose of Swinburne’s test?

Unit-IV

1. What is transformation ratio?

2. Why iron losses are are treated as constant losses?

3. What is a step up transformer?

4. If the copper losses at 25% of full load are 100W. Find the copper losses at full load.

5. Why is Open circuit test conducted on LV side of a transformer?

6. What is the importance of All day efficiency?

7. Define Voltage regulation.

8. If Iron losses and copper losses of a transformer are 100W and 25 W respectively. Find the load at

which efficiency is maximum.

9. Draw the family of efficiency curves for various power factors.

10. What are the conditions that should be considered for an ideal transformer?

Unit-V

1. Draw the torque-speed characteristic of a three-phase induction motor and explain its shape.

2. What is the condition for maximum torque developed at starting?

3. What is the expression for maximum torque developed in a three-phase induction motor?

4. Draw the power-flow diagram in an induction motor

5. Mention various applications of three-phase induction motors

6. Why the core of the induction motor is made of laminations?

7. What are slip rings?

8. What happens, if you insert a resistance in the rotor circuit?

9. What are the various losses in an induction motor? State the factors on which they depend.

10. Why the rotor bars are skewed in a squirrel cage rotor?

PART-B

Unit-I

1. Illustrate Tellegan’s theorem from the circuit shown.

2. Use superposition theorem to determine through the 4Ω resistor, for the network shown

3. Verify reciprocity theorem for the network shown

4. Find the current through the 4Ω resistor using Thevenin’s theorem

5. Find the current through the 30Ω resistor in the network shown, using Norton’s theorem.

6. Find the value of RL in the circuit shown for the maximum power transferred form source to load.

Also find the maximum power transferred

7. Using Millman’s theorem, determine the current through RL in the network shown

8. Find the current through the 20Ω resistor of the network shown, using Norton’s theorem

9. Find the voltage ‘V’, across the 20Ω resistor in the network shown, using superposition theorem.

10. Find the current through 6Ω resistor of the network shown using Millman’s theorem

Unit-II

1. For RC series circuit with switch using DC transients

2

2(0 ) (0 )

,dt d i

dt dt

+ +

2. For RL series circuit R=13Ω, L=19 H is suddenly connected to DC supply of 50 F calculate

i) Initial rate of change of current time constant

3. Calculate current after t=5.5 sec in series RL circuit having R=2.8Ω & L=13.2H. a DC voltage of 120V

is applied to circuit

4. A RLC circuit connected to switch and it closes at

5. Find, 2

(0 ) (0 )(0 ), ,

di dt ii

dt dt

+ ++

6.

Find

2

2(0 ) (0 )

(0 ), ,di d i

idt dt

+ ++

7.

Find V,

2

2&dv d v

dt dt at t=0

+

8.

In a network K is opened at t=0, Calculate

2

2, &dv d v

vdt dt

at 0t +=

9. Derive the expression for transient current in RC circuit with zero initial conditions.

10. If the switch is closed at t=0 there is a charge of 500μC on a capacitor with polarity as shown, find

2

2,dV d V

dt dt

Unit-III

1. With usual notations derive an expression for the induced E.M.F of a D.C.Machine

2. The induced emf in a dc generator running at 750 rpm is 220V.Calculate

(a)the speed at which the induced emf is 250V(assume the flux to be constant)

(b) the required percentage increase in the field flux so that the induced emf is250V,while the speed

is only 600rpm.

3. What is meant by external characteristics of dc generator? Why does the external characteristic of a

dc shunt generator droop downwards?

4. A series motor runs at 600 rpm when taking 110A from 250V supply. The resistance of the armature

circuit is 0.12 Ω and that of series winding is 0.03Ω.The useful flux per pole for 120A is 0.024Wb and

that of 50A is 0.0155Wb.Calculate the speed when the current has fallen to 50A.

5. Explain the principle of operation of a DC Machine as

(a)a generator (b)a motor

6. A dc shunt generator, with shunt-field resistance of 52.5Ω, supplies full-load current of 195A at

210V.Its full-load efficiency is 90% and it has stray losses of 710W.Determine its armature resistance

and the load current corresponding to maximum efficiency.

7. What is OCC Characteristics of a DC generator? What is its significance?

8. A 120V,DC shunt motor has an armature resistance of 0.2Ω and field resistance of 60Ω.It runs at

1800rpm,when it takes a full load current of 40A.Find the speed of motor when it is operating with

half full load.

9. How to find the efficiency of a dc generator using Swinburne’s test?

10. A 250V shunt motor have an armature resistance of 0.5Ω and field resistance of 250Ω.When driving

at 600rpm on load the torque of which is constant the armature takes 20A.If it be desired to raise

the speed from 600rpm to 800rpm what resistance must be inserted in the shunt field circuit,

assuming the magnetization curve to be a straight line

Unit-IV

1. Draw the phasor diagram for the practical transformer on no load.

2. Describe the construction of a core type transformer.

3. Describe the method to perform OC and SC test on a transformer.

4. Discuss about the constant losses in a transformer.

5. Explain the determination of deducing equivalent circuit parameters.

6. Discuss the principle of operation of the single phase transformer.

7. Derive the condition to have the maximum efficiency .

8. Explain the concept of regulation in detail, in the case of transformers.

9. Discuss the types of transformers based on their application

10. The nameplate on a 50KVA transformer (core type) shows a primary voltage of 480V and a

secondary voltage of 120V. 3 –turns of wire are wound around the external winding and a voltmeter

is connected across this 3-turn coil. A voltage of 76V is then applied to the 120V winding and the

voltage across 3 –turn winding is found to be 0.93V. Determine the approximate number of turns on

the 480V and 120V windings

Unit-V

1. Show that stator magnetic field and the field produced by the rotor mmf are stationary with respect

to each other.

2. Draw the connection diagram for a manual star-delta starter

3. If the applied voltage is reduced to half, what will be the reduction in torque developed?

4. Prove that in an induction motor the rotor copper loss is slip times the rotor input.

5. A 4-pole induction motor is run at 1450 rpm from a 50Hz supply. Find the percentage slip and the

frequency of rotor current.

6. If the emf in the stator of a 4-pole, 3-phase induction motor has s frequency of 50Hz and that in the

rotor is 1.5Hz, at what speed is the motor running and what is the slip?

7. A 3-phase, 50 Hz, 4-pole induction motor has a full load slip of 0.06. Find frequency of rotor current

at the instant of starting and at full load.

8. A3-phase induction motor develops starting torque, but a one-phase induction motor does not

develop a starting torque. Why?

9. Why is auxiliary winding in a capacitor-start motor disconnected, after the motor has picked up

speed?

10. The Power Factor of Induction motor on no-load is very poor, why?