Code No:310203

III-B-Tech I-Semester Regular Examinations

May/June-2004
Set No. 3

POWER SYSTEM – II

(Electronics and Instrumentation Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. a) What do you understand by the constants of an over head line?

b) Derive an expression for the loop inductance of a single phase line. Also calculate loop inductance per km if distance between conductors is 1.5mtr and radius of each conductor 1.2cm.

2. a) A 3-phase over head transmission line has its conductors arranged at the corners of an equilateral triangle of 2cm side. Calculate capacitance of each conductor if the diameter of each conductor is 1.52cm.

b) A 3-phase m50Hz, 66KV over head line conductors are placed in a horizontal plane as shown in the figure.

DIAGRAM

The conductor dia is 1.2cm .If the line length is 100km, calculate (i) capacitance per phase (ii) charging current per phase. Assume the line is transposed.

3. a) Discuss why Ferranti effect is significant only in medium and long line?

b) What are tuned power lines?

c) The ABCD constants of a lossless three phaser, 500KV transmission line arem

A=D=0.86+j0           B=0+j130.2              C=j0.002

Obtain the sending end quantities and the voltage regulation when line delivers 1000MVA at 0.8power factor lagging at 500KV.

4. A three-phase 66KV transmission line is carried by strings of 5 suspension insulators. The capacity of each unit insulator to the capacity relative to earth is 4:1. Calculate the potential across each unit and the string efficiency. Assume that there is no leakage.

5. An overhead line is erected across a span of d250m on level supports. The conductor has a diameter of 1.42cm and has a dead weight of 1.09Kg per meter. The line is subjected to wind pressure of 37.8Kg per square meter of the projected area. The radial thickness of ice is 1.25cm. Calculated the sag
a) in an inclined direction b) in a vertical direction

Assume a maximum working stress 1,050Kg sq. cm. One cubic meter of ice weights 913.5Kg.

6. a) Derive an expression for capacitance of a single core cable.

b) A 66KV single core lead sheathed cable is graded by using two dielectrics of relative permitting 5 and3 respectively. Thickness of each dielectrics is 1 cm. Determine the maximum electrostatic force in the two dielectrics.

7. a) What is most economical power factor? It is needed?

b) List the methods to improve power factor and explain briefly.

c) Show that the most economical power factor depends upon the relative costs of supply and p.f. Correction equipment.

8. a) Bring out the relationship between symmetrical components and unbalanced phasors.

b) Determine the unbalanced phase Voltage VR, VY and VB in a circuit where

c) Resolve the sequence currents into unbalanced currents. Given IRO = (8+j5.33) Amps, IR1 = (0.845+j15.11) Amps and IR2 = (3.155+j3.56) Amps.