Code No:310203

III-B-Tech I-Semester Supplementary Examinations

June-2003
Set No. 4

POWER SYSTEM – II

(Electrical and Electronics Engineering)

[Time:3 hours]
Max. Marks:80

Answer any FIVE questions

ALL questions carry equal marks

1. a) Develop an expression for the inductance of a single phase transmission line taking into account the internal flux linkages. Assume the conductors are solid.

b) Calculate the inductance per Km per phase of a 3-phase transposed line. With distance between any two conductors being 4m,4, and 8meters respectively.

2. a) How do we find line to neutral capacitance in a 3- phase system?

b) The three conductors R, Y and B of a 3-phase line are arranged in a horizontal plane with D_RY = 1.5m; D_YB = 2m and D_BR = 3.5m. Find line to neural capacitance per km if dia of each conductors is 1.2 cm. The conductors are transposed at regular intervals. Also calculate line capacitance per km length.

3. a) What is a nominal circuit? Find ABCD constants for nominal pi circuit of a transmission line.

b) A 300Km 3 phase overhead line has a series impedance of 11+j106 ohms per phase and a shunt admittance of 1.13 milli mho per phase. The line delivers 250MW at unity power factor and at 275KV. Find (i) A, B, C, D constants (ii) sending end voltage (iii) power angle.

4. a) Discuss why Ferranti effect is significance only in medium and long lines?

b) What are tuned power lines?

c) The ABCD constants of a lossless three phase, 500KV transmission line are
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 0.8 power factor lagging at 500KV.

5. An overhead line has a conductor of cross -section 2.5cm² hard drawn copper and a span length of 150meters . Determine the sag which must be allowed if the tension is not to exceed one-fifth of the ultimate strength of 4,175Kg/Cm².

a) in still air and
b) with a wind pressure of 1.3kg/meter and an ice coating of 1.25cms.
Determine also the vertical sag in the latter case.

6. a) What are the limitations of solid type cables? Explain any other kind of cable to overcome the limitations.

b) A single core lead covered cable is to be designed for 66KV to earth. Its conductors radius is 0.5cm and its three insulating materials. A, B, and C have relative permittivities 4, 4.5 and 2.5 with maximum permissible stresses of 50, 40 and 30 KV/cm respectively. Find the minimum internal diameter of the lead sheath.

7. a) Explain the concept of power factor.

b) Explain any three causes of low power factor of supply system.

c) Discuss the disadvantages of low power factor and list methods to improve power factor

8. a) What are symmetrical components ? Why they are necessary?

b) A 3-phase unbalanced system currents are read as I_R = 150A, I_Y phase sequence is RYB. Find all the three symmetrical components for the case.