Important Short Questions and Answers: Transmission Line Parameters

37.Define inductance of a line.

It is defined as the loop inductance per unit length of the line .Its unit is henrys per meter.

38.Define capacitance of a line.

It is defined as shunt capacitance between the two wires per unit line length. Its unit is farads per meter.

39.What is skin effect?

The steady current when flowing through the conductor ,does not distribute uniformly, rather it has the tendency to concentrate near the surface of the conductor. This phenomenon is called skin effect.

40.Why skin effect is absent in dc system?

The steady current when flowing through a conductor distributes itself uniformly over the whole cross section of the conductor .That is why skin effect is absent in dc system.

41.What is the effect of skin effect on the resistance of the line?

Due to skin effect the effective area of cross section of the conductor through which current flow is reduced. Hence the resistance of the line is increased when ac current is flowing.

42.On what factors the skin effect depend?

Nature of the material, Diameter of the wire , Frequency and shape of the wire.

43.Define symmetrical spacing.

In 3 phase system when the line conductors are equidistant from each other then it is called symmetrical spacing.

44.What is the necessity for a double circuit line?

To reduce the inductance per phase and to increase the efficiency.

45.Mention the factors governing the inductance of a line.

Radius of the conductor and the spacing between the conductors.

46.Define a neutral plane.

It is a plane where electric field intensity and potential is zero.

47.Define proximity effect.

The alternating magnetic flux in a conductor caused by the current flowing in a neighbouring conductor gives rise to a circulating current which cause an apparent increase in the resistance of the conductor .This phenomenon is called as proximity effect.

48.What is the effect of proximity effect?

It results in the non uniform distribution of current in the cross section, and the increase of resistance.

49.What is a composite conductor?

A conductor which operates at high voltages and composed of 2 or more subconductors and run electrically in parallel are called composite conductors.

50.What is a bundle conductor?

It is a conductor made up of 2 or more sub conductors and is used as one phase conductors.

51.Mention the advantages of using bundled conductors.

Reduced reactance, reduced voltage gradient , reduced corona loss .reduced interference

52.What is meant by transposition of line conductors?

Transposition means changing the positions of the three phases on the line supports twice over the total length of the line .the line conductors in practice ,are so transposed that each of the three possible arrangements of conductors exit for one-third of the total length of the line .

53.Define bundled conductors?

The use of more than one conductor per phase is called bundled conductors.

54.What is skin effect?

The phenomenon of concentration of an ac current near the surface of the conductor is known as skin effect.

55.On what factors does the skin effect depends?

The skin effect depends upon the 1, type of the material 2, frequency of the current 3, diameter of conductor& shape of conductor. It increases with the increase of cross-section, permeability and supply frequency.

56.Define voltage regulation.

Voltage regulation is defined as the change in voltage at the receiving (or load) end when the full-load is thrown off, the sending-end (or supply) voltage and supply frequency remaining unchanged ..

% voltage regulation= ((Vs-Vr)/Vr)*100

where Vs is the voltage at the sending end

Vr is the receiving end voltage.

57.Define proximity effect.

The alternating magnetic flux in a conductor caused by the current flowing in a neighbouring conductor gives rise to a circulating current which cause an apparent increase in the resistance of the conductor .This phenomenon is called as proximity effect.

58.Define transmission efficiency.

Efficiency defined as the ratio of power delivered at the receiving end to the power sent from the sending end .

59.Define Ferranti effect .

The phenomenon of rise in voltage at the receiving end of the open circuited or lightly loaded line is called the Ferranti effect .

60.What are the units of ABCD (generalised) constants of a transmission line ?

A and D are dimensionless B is in ohms and C is in Siemens (mhos)

61.Mention the range of surge impedance in underground cables .

40-60 ohms

62.Mention the range of surge impedance in overhead transmission lines .

400-600 ohms