The document discusses various concepts related to electric fields, potential differences, and capacitance in transmission lines. It emphasizes the behavior of charged conductors, the effect of charging currents, and the conditions under which capacitance effects become significant. Additionally, it addresses potential calculations in electrical systems and offers multiple-choice questions related to capacitance.

2. • Introduction
• Electric field & potential difference
• Potential at a charged conductor in a group of
charged conductor
• Capacitance of single phase 2 wire transmission
line
Content

3. Introduction

4. • When an A.C, voltages applied on transmission
line the charge on the conductor at any point
increase & decreases with increase & decreases
in the instantaneous value of the voltage.
• This result in flowing of current between
conductor.
• This charging current is also flow when
transmission line is open circuited.

5. • This charging current causes the voltage drop
along the transmission line .
• The capacitor effect mainly observed above 100 kv
& 150 km length which is treated as long
transmission line.
• Below this voltage level the capacitance effect is
negligible.

6. Electric field & potential difference
• The electric field E at a given point is defined as the force
F that would be exerted on a stationary test particle of
unit charge by electromagnetic force.
• SI unit are newtons per coulomb ( N/C ).

7. • Electric potential is defined as the work done
in moving a unit positive charge from infinity
to that point.
• Potential difference is the difference in
electric potential energy between two points
per unit electric charge.
• Potential difference is measured in units of
volts ( joule/coulomb ).

8. Potential at a charged conductor in a group of charged
conductor

9. • We consider a group of long straight conductors
A,B,C,D…N having charges QA, QB...QN refer in fig.
• Potential at A due to its own charge (QA)
= ………………. (1)

10. • Potential at conductor A due to charge (QB)
= ………………. (2)
• Potential at conductor A due to charge (QC)
= ………………. (3)

11. • Overall potential difference between conductor
and infinite neutral plane is
• VA = (1)+(2)+(3)+...
• VA = + + +...
• VA =

12. Capacitance of single phase 2 wire transmission line

13. • Consider a single-phase transmission line.
• It consists of two parallel conductor A & B,
having radius r meters at a distance D meters.
• Let their respective charge be +Q & -Q coulombs
per meter length.
• The total potential difference between
conductor A & neutral infinite plan is

14. =
=

15. • potential difference between conductor B & A

16. • Both these potentials are write the same neutral plane
potential difference between the conductor is

17. MCQ’s
(i) If the length of the line is decreased, its capacitance is…….
(ii) If capacitance between two conductors of a 3-phase line is 4 µF,
then capacitance of each conductor to neutral is ..................
(iii) ………..condition the capacitance current is also arrives.

18. Answer
(i) decrease
(ii) 8 µF
(iii) No load condition