Page 315 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Fig 2 Fig 3

3 For the same load and sending end voltage, the voltage drop in DC transmission lines is less than that in AC
transmission.
4 As there is no skin effect on conductors, therefore entire cross - section of conductor is usefully utilized thereby
affecting saving in material.
5 For the same value of voltage insulating material on DC lines experience less stress as compared to those on
AC transmission lines.

6 A DC line has less corona loss and reduced interference with communication circuits.
7 There is no problem of system instability which is so common in AC transmission.
Disadvantages of DC transmission
1 Generation of power at high DC voltages is difficult due to commutation problems and cannot be usefully
utilized at consumer ends.
2 Step up or step -down transformation of DC voltages is not possible in equipment like transformer.
Advantages of AC electric power transmission
1 Power can be generated at high voltages as there is no commutation problems.

2 AC voltages can be conveniently stepped up or stepped down by using transformers.
3 High voltage transmission of AC power reduces losses.
Disadvantages of AC electric power transmission
1 Problems of inductances and capacitances exist in transmission lines.
2 Due to skin effect, more copper is required.

3 Construction of AC transmission lines is more complicated as well as costly.
4 Effective resistance of AC transmission lines is increased due to skin effect.

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CITS : Power - Electrician & Wireman - Lesson 106-116