introduction electrical field of a long straight conductor potential difference between two...
TRANSCRIPT
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• 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
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Introduction
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• 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.
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• 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.
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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 ).
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• 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 ).
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Potential at a charged conductor in a group of charged conductor
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• 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)
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• Potential at conductor A due to charge (QB)
= ………………. (2)
• Potential at conductor A due to charge (QC)
= ………………. (3)
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• Overall potential difference between conductor and infinite neutral plane is
• VA = (1)+(2)+(3)+...
• VA = + + +...
• VA =
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Capacitance of single phase 2 wire transmission line
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• 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
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=
=
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• potential difference between conductor B & A
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• Both these potentials are write the same neutral plane potential difference between the conductor is
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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.
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Answer
(i) decrease
(ii) 8 µF
(iii) No load condition
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