Transmisison Line Shunt Capacitance

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SUMMARY

Shunt capacitance is a critical factor in transmission lines, particularly in power transmission lines due to their high voltages and extensive lengths, which can reach up to a thousand miles. This capacitance, often referred to as stray capacitance, becomes significant in long-distance power grid simulations, especially for lines exceeding one kilometer. Unlike normal circuits, where capacitance is negligible, transmission lines exhibit capacitance due to their interaction with the ground and the surrounding environment. The formula for capacitance (C = Q/V) indicates that while higher voltages typically suggest lower capacitance, the dynamics in real-world applications complicate this relationship.

PREREQUISITES
  • Understanding of transmission line theory
  • Knowledge of electrical capacitance and the formula C = Q/V
  • Familiarity with power transmission systems
  • Basic principles of electrical engineering
NEXT STEPS
  • Research the impact of shunt capacitance in power transmission line design
  • Explore transmission line models used in electrical engineering
  • Learn about the effects of high voltage on capacitance in power systems
  • Investigate the differences between three-phase and single-phase power lines
USEFUL FOR

Electrical engineers, power system designers, and students studying transmission line theory will benefit from this discussion, particularly those focusing on the implications of shunt capacitance in high-voltage power transmission.

yabb dabba do
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Why is there a shunt capacitance in a transmission line, but not in a normal circuit (non-transmission line).?
 
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yabb dabba do said:
Why is there a shunt capacitance in a transmission line, but not in a normal circuit (non-transmission line).?

Do you mean a power transmission line? If yes, it is because power lines have very high voltages, and their length can be hundreds or even a thousand miles. So called stray capacitance is quite significant in those conditions.

The phrase transmission line also applies to communications. They should not be confused with power transmission lines.
 
anorlunda said:
Do you mean a power transmission line? If yes, it is because power lines have very high voltages, and their length can be hundreds or even a thousand miles. So called stray capacitance is quite significant in those conditions.

The phrase transmission line also applies to communications. They should not be confused with power transmission lines.

I think the same transmission line models are used as long as the length of the transmission line is quite long relative to wave length
 
yabb dabba do said:
I think the same transmission line models are used as long as the length of the transmission line is quite long relative to wave length
In power grid simulations, we include shunt capacitance in all lines longer than about one kilometer. It has nothing to do with wavelength.

Three phase, three wire, power lines are very different than single phase, two wire lines.
 
anorlunda said:
Do you mean a power transmission line? If yes, it is because power lines have very high voltages.

But formula for capacitance is C = Q/V.
So higher voltage, lower capacitance... ?
 
jaus tail said:
But formula for capacitance is C = Q/V.
So higher voltage, lower capacitance... ?

Higher voltages interact more with the ground, so Q is not constant.

You have to be careful with formulas in real life. Like designing a higher voltage power line. Many things other than V will change.
 
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yabb dabba do said:
Why is there a shunt capacitance in a transmission line, but not in a normal circuit (non-transmission line).?
Every wire in every circuit has capacitance. It exists, for instance, between the conductors of a telephone line, and also between every conductor and the rest of the Universe.
 

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