3 phase transmission line mutual coupling

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Discussion Overview

The discussion revolves around the effects of mutual coupling in a three-phase transmission line during fault conditions. Participants explore the discrepancies between calculated fault currents using symmetrical component analysis and those measured in physical simulations, focusing on the role of mutual inductive coupling and its implications for current measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether mutual coupling affects the current through each line during a fault, noting that their calculated fault current values are consistently higher than those obtained from physical simulations.
  • Another participant suggests that the inductors used in the simulation represent mutual inductive coupling between the lines, implying that this could influence the results.
  • A participant describes their setup using a three-phase inductive load bank and notes that their theoretical calculations yield currents that are approximately 0.1A higher than the measured values, raising the question of whether mutual coupling could explain the lower measured values.
  • One participant states that the inductivities of the conductors increase the total reactance seen by the source, suggesting that this could lead to smaller fault currents further from the source.

Areas of Agreement / Disagreement

Participants express differing views on the impact of mutual coupling on fault current measurements, with no consensus reached regarding its specific effects or the reasons for discrepancies between calculated and measured values.

Contextual Notes

The discussion highlights potential limitations in the calculations, particularly regarding the treatment of mutual coupling and its effects on measurements, but does not resolve these issues.

Physicist3
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Hi, if I simulate a three phase transmission line operating with a fault across two of the phases, would the mutual coupling have any effect on the current through each of the lines, as I have calculated the fault current values using symmetrical component analysis and the values are consistently slightly higher than those obtained from physical simulation testing using a three phase transmission line that I have constructed using an inductor and resistor in series per phase?
 
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The inductors values represent mutual inductive coupling between two lines in this case. Maybe you used values for line to ground return fault (which are close but identical)
 
What I have done is used a 3 phase inductive load bank to simulate a transmission line. I have then (using the known inductance and resistance values from this load bank), used symmetrical component analysis to calculate the theoretical currents through the system and these are all about 0.1A above the values measured from testing of the physical system. Because the calculations will not take the mutual coupling values between the phases into account, but the mutual coupling will still affect the measured results, would this cause the measured values to be slightly lower than the calculated ones?
 
Inductivities (and hence reactances) of the conductors of a transmission line increase total reactance seen by source powering the fault. Therefore, the fault current will be smaller far away from the source.
 

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