Performance of Transmission Lines, Line Parameters and Corona

1. If the conductor radius increases, inductance of the line________.

a. Decreases

b. Increases

c. Remains same

d. May increase or decrease

 

2. For an underground cable, the surge impedance is generally taken as_______.

a. 40 ohm

b. 80 ohm

c. 100 ohm

d. 400 ohm

Reason: For underground cable, Z_s= 40 ohm

                 For overhead line, Z_s= 400 ohm

 

3. Consider the following phenomenon occurring in a power system:

(i) Corona loss       

(ii) Charging Current

(iii) Ferranti effect

 (iv) Dielectric loss

(v) Skin effect

a. (i), (iii) and (v)

b. (ii), (iii), (iv) and (v)

c. (ii), (iii) and (iv)

d. (i), (ii), (iii) and (v)

Reason: Dielectric loss occurs in underground cable not in transmission line.

 

4. The resistance and reactance of short line are equal. At zero regulation the load will be________.

a. UPF

b. ZPF

c. 0707 lag

d. 0707 lead

 

5. Shunt reactors are needed_______.

a. To boost receiving end voltage under light loads

b. To boost receiving end voltage under heavy loads

c. To bring down receiving end voltage at light loads

d. To bring down receiving end voltage under heavy loads

 

6. Operating transmission lines close to their maximum power transfer capability will impair_________.

a. Stability

b. Steady state power flow

c. Voltage profile

d. Transmission efficiency

 

7. The transmission efficiency increases with________.

a. Decrease in pf and increase in voltage level

b. Decrease in pf and decrease in voltage level

c. Increase in pf and increase in voltage level

d. Increase in pf and decrease in voltage level

 

8. The surge impedance loading of a 220 kV overhead line is approximately_______.

a. 121 MW

b. 1.21 MW

c. 12.1 MW

d. 121,000 MW

 

9. A lossless line terminated with its surge impedance has a__________.

a. Sag of voltage at midpoint

b. Swell of voltage at midpoint

c. Flat voltage profile

d. Uniform voltage dips along length of line

 

10. The economic size of conductor is determined by__________.

a. Kirchhoff’s law

b. Kelvin’s law

c. Faraday’s law

d. All of these

 

11. Skin effect depends upon_________.

a. Type of conductor material

b. Shape of the conductor

c. Both (a) and (b)

d. None of the above

Reason: Skin effect depends upon type of conductor material, shape of conductor, frequency of current and diameter of conductor.

 

12. Proximity effect depends upon__________.

a. Size of the conductor

b. Resistivity of material

c. Permeability of the material

d. All of the above

Solution: Like skin effect, proximity effect depends on the conductor size, frequency of the supply, resistivity and relative permeability of the material.

 

13. In a transmission system, the weight of copper used is proportional to__________.

a. E²

b. E

c.1/ E²

d. 1/E

 

14. As the spacing between the phase conductors are increased, match List-I with List-II and select the correct code given below the lists:                                      

List-I	List-II
A. Line resistance	1. Decrease
B. Line inductance	2. Increase
C. Line capacitance	3. Remains same

 

Codes :

	A	B	C
a.	1	2	2
b.	1	3	2
c.	3	1	2
d.	3	2	1

 

15. Which of the following conductor spirality effect is ignored?

a. Magnetic

b. Non-magnetic

c. Both (a) and (b)

d. None of these

 

16. Skin effect is ignored in which supply system?

a. AC

b. DC

c. Both

d. None of these

Solution: In case of DC, current is uniformly distributed throughout the conductor surface.

 

17. For a good voltage profile under no load conditions a long line needs________.

a. Shunt capacitor at sending end

b. Shunt resistance at receiving end

c. Shunt reactors at receiving end

d. Shunt capacitors at receiving end

20. Corona can be reduced by use of hollow conductor because_________.

a. The current density is reduced

b. The eddy current in the conductor is eliminated

c. For a given cross-section, the radius is increased

d. Of better ventilation in the conductor 

21. The charging current in a transmission line_______.

a. Lags the voltage by 90° 

b. Leads the voltage by 45°

c. Leads the voltage by 90°

d. Leads the voltage by 180°

Reason: Charging current is the current flowing through capacitance of the transmission line which leads the supply voltage by 90°. 

22. Which of the following relationships is not valid for a short transmission line ?

a. I_S =  I_R

b. B = Z = C

c. A = D = 1

d. None of these

Reason: For a short transmission line, B = Z and C = Y = 0 i.e. capacitance is neglected due to which Y = 0.

23. Sag of an overhead line is proportional to the square of_________.

a. Tension

b. Span

c. Temperature

d. Weight of conductor

Reason: Sag, S = Wl²/8T

∴  S ∝ l² ∝ (span)²

24. The charging reactance of 100 km line is 500 Ω, the charging reactance of 200 km length line will be________.

a. 1000 Ω

b. 250 Ω

c. 500 Ω

d. 1255 Ω

Reason: Charging reactance of a line ∝ (1 / (length of the line))

As the length of line doubles, charging reactance will reduce to half.

25. When bundle conductors are used in place of single conductors, the effective inductance and charging current will respectively________.

a. Decrease and increase

b. Increase and decrease

c. Decrease and remain unaffected

d. Remain unaffected and increase

Reason: Bundle conductors increases self GMD therefore, inductance will decrease while capacitance will increase. Due to increase in capacitance, charging current will increase.