Power Transmission through Transmission Lines

Click For Summary

Discussion Overview

The discussion revolves around the behavior of power transmission through transmission lines, specifically focusing on the constancy of power factor (pf) and current in relation to varying loads. Participants explore the implications of load changes on numerical examples and the assumptions made in AC analysis.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • Some participants question whether power factor and current can truly be constant given that loads frequently change, suggesting that this variability would affect the current waveform.
  • Others argue that while loads do change, it is still valid to quote average or specific values for convenience in numerical examples.
  • One participant notes that if the current waveform is plotted over time, it would exhibit variable amplitude due to changing loads, but specific values are often used for simplification in calculations.
  • Another participant explains that AC analysis assumes an average over cycles, even when the average is time-variant, and acknowledges the common oversight regarding static AC analysis versus time-varying averages.
  • There is a comparison made to real-life scenarios, such as a car changing speed, emphasizing that while conditions may vary, calculations often start from simplified assumptions.

Areas of Agreement / Disagreement

Participants express differing views on the constancy of power factor and current in practical scenarios. While some acknowledge the variability due to changing loads, others maintain that using average values is acceptable for analysis. The discussion remains unresolved regarding the implications of these assumptions.

Contextual Notes

Participants highlight the limitations of assuming constant values in the context of dynamic loads, indicating a dependence on definitions and the nature of AC analysis. The discussion reflects an awareness of the complexities involved in real-world applications.

cnh1995
Homework Helper
Gold Member
Messages
3,489
Reaction score
1,163
In the numericals based on transmission line, the wording is like this-" A transmission line feeds power to a load at 132kV, 0.8 pf lagging and so on." In practice, are pf and
current really constant? Doesn't it depend on the load? I mean, every minute someone is switching something on and something off. If the current waveform for a minute is plotted, how will it look? Will the pf be constant? By pf , I mean transmission line pf.
 
Engineering news on Phys.org
cnh1995 said:
In the numericals based on transmission line, the wording is like this-" A transmission line feeds power to a load at 132kV, 0.8 pf lagging and so on." In practice, are pf and
current really constant? Doesn't it depend on the load? I mean, every minute someone is switching something on and something off. If the current waveform for a minute is plotted, how will it look? Will the pf be constant? By pf , I mean transmission line pf.

Yes, of course the loads change all the time. That doesn't mean that you can't quote an average value or a specific value as an example.
 
  • Like
Likes   Reactions: cnh1995
anorlunda said:
Yes, of course the loads change all the time. That doesn't mean that you can't quote an average value or a specific value as an example.
So, if the current waveform for a minute is plotted, it has to be of variable amplitude(provided the load is changning). But for the numericals, some specific value is taken for convenience, right?
 
It is a simplification. AC analysis with P+jQ does assume an average over an integral number of pure cycles. But we also use it when the average is time variant. We simply ignore the distortions in the sinusoidal. Nevertheless, the approximations are highly accurate and often verified.

Most students never realize the apparent contradiction between "static" AC analysis and time varying averages. Good for you.
 
  • Like
Likes   Reactions: cnh1995
cnh1995 said:
I mean, every minute someone is switching something on and something off.
And when a car goes along the road, it will keep changing its velocity and power output.That doesn't stop us from doing calculations about a specific set of conditions. Things can rapidly get very complicated in real life so we have to start with a simple case.
 
  • Like
Likes   Reactions: cnh1995

Similar threads

  • · Replies 21 ·
Replies
21
Views
3K
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 39 ·
2
Replies
39
Views
10K
Replies
4
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 14 ·
Replies
14
Views
18K
  • · Replies 69 ·
3
Replies
69
Views
9K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K