Alternator on a long transmission line

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Discussion Overview

The discussion revolves around the potential dangers of connecting an alternator to a long transmission line, particularly when the line has high capacitance. Participants explore the implications of transmission line length, frequency, and power factors on the safety and functionality of such a connection.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express concern about the dangers of connecting an alternator to a long transmission line with high capacitance, questioning the reasons for potential hazards.
  • One participant notes that connecting a quarter wavelength of open circuit transmission line to an alternator could appear as a short circuit, particularly for very long lines at standard frequencies (50 or 60 Hz).
  • It is mentioned that a regular length transmission line behaves like a capacitor, affecting the power factor (PF) seen by the alternator, which could lead to increased current demands.
  • Another participant suggests that high capacitance can lead to an increase in voltage due to the interaction between the stator and rotor magnetic fields, which could be dangerous.
  • Concerns are raised about the presence of lethal voltages in isolated lines, emphasizing the risks associated with long transmission lines and capacitance.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the safety of connecting an alternator to a long transmission line with high capacitance. Multiple viewpoints and concerns are expressed, indicating ongoing debate and uncertainty.

Contextual Notes

Participants mention various factors such as line length, frequency, and operating power, but do not provide specific definitions or assumptions that might clarify the discussion further. The implications of power factor and current handling are noted but remain unresolved.

samieee
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Could it be dangerous to connect an alternator to a long transmission line,if the line has high capacitance?if dangerous then why? please explain...
 
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How long, what frequency and what operating power?
If you connect a quarter wavelength of open circuit transmission line to your alternator, then it will look like a short circuit. This is only relevant for very long transmission lines (trans continental style) at 60 or 50 Hz.
A 'short' / regular length of transmission line will be, effectively, a capacitor, with a value of a few tens of pF per metre of line. This will affect the Power Factor of the load seen by the alternator. You would need to know what PF the particular alternator can cope with and at what output power.
The problem is that, to deliver a given Power, a PF which is less than unity (1) will require more current for a given voltage than the 'Power =Volts times Amps' would suggest. This is because the capacitor will need to charge and discharge, requiring current to flow in addition to the current in the (resistive) load. This current is not in phase with the voltage so there is no 'useful power' involved - just extra current handling demand on the cables and alternator windings.
 
Last edited:
samieee said:
Could it be dangerous to connect an alternator to a long transmission line,if the line has high capacitance?if dangerous then why? please explain...

What is the context of your question? What kind of alternator? Is this for schoolwork?
 
berkeman said:
What is the context of your question? What kind of alternator? Is this for schoolwork?
I didn't realize this thread was started by samieee when I posted a reply to their thread asking about https://www.physicsforums.com/showthread.php?p=2601746#post2601746". Hopefully they will realize it is not a trivial process.
 
Last edited by a moderator:
sophiecentaur said:
How long, what frequency and what operating power?

berkeman said:
What is the context of your question? What kind of alternator?

any kind of alternator,any frequency (let assume it as supply frequency).Any way i got the answer,the anser is :It is dangerous,because at high capacitance(leading power factor) the stator MMF will aid the rotor MMF thus the voltage will increase at large magnitude.which is not desired.
 
One of the problems with long transmission lines and capacitance is that even if the line is isolated there is the posibility of lethal voltages still being present in the lines. Put into circuit Earth and prove dead.
 

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