Can an iron core both generate and absorb vars?

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I guess thats it.

But what about feeders and transmission lines where you close a tie point and then VARs change?
 
Transmission lines have capacitance, so the load plays a role here.
As long as the two transformers have the same phase shift, I do not see how paralleling them could change the VARs delivered to their individual primaries.
 
GoldDigger said:
Transmission lines have capacitance, so the load plays a role here.
As long as the two transformers have the same phase shift, I do not see how paralleling them could change the VARs delivered to their individual primaries.
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I'll take your word for it.
 
GoldDigger said:
As long as the two transformers have the same phase shift, I do not see how paralleling them could change the VARs delivered to their individual primaries.
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you won’t get them together unless they do...
 
GoldDigger said:
How does paralleling them affect the magnetizing current? That is where the VARs appear.
The unloaded currents will definitely change, but the real component of the power is where the change is seen.
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I meant unless they have the same phase shift they won’t parallel. Or if you manage to get them together (If they’re small enough) I doubt they will last long.
 
Hv&Lv said:
I meant unless they have the same phase shift they won’t parallel. Or if you manage to get them together (If they’re small enough) I doubt they will last long.
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I understand that there will be very small differences in phase shift based on %Z even for the same winding geometry. That is what I was referring to, not the sort of major phase shifts that can be seen in three-phase transformers with different geometries.
 
Hv&Lv said:
I meant unless they have the same phase shift they won’t parallel. Or if you manage to get them together (If they’re small enough) I doubt they will last long.
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Right, like Dyn01 against a Dyn11 or Ynyn0 against a Dyn11.

Im talking about identical transformers set on different taps. I know you know this but just clarifying.
 
mbrooke said:
Seems you're right... can a 180* phase shift really be called "reactive"?


https://imgur.com/cQp8vEK
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I see what seems to me to be a fundamental problem with the above analysis, namely that the for the unloaded case with the two transformers in parallel the circulating current must be purely resistive. What is it about the loaded case that suddenly makes the circulating current purely reactive?
 
mbrooke said:
Seems you're right... can a 180* phase shift really be called "reactive"?
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I think I was trying to express that in one of my responses.

To restate differently, we commonly say that loads where the current lags the voltage (inductive loads) 'consume' VARs, and that loads where the current leads the voltage (capacitive loads) 'supply' VARs.

In the case of the circulating currents, the current flows out of the 'top' of one winding, into the 'top' of the other winding, then out of the 'bottom' of the second winding and into the 'bottom' of the first winding. (Yes, the current is alternating....) The point being that the phase angle of the current referenced to one winding is always going to be 180 degrees out of phase as when referenced to the other winding.

This 180 degree phase difference is what means that one winding is supplying power to the circulating current, and one winding is consuming power from the circulating current. Similarly, if one winding is supplying inductive VARs to the circulating current the other winding must be consuming inductive VARs from the circulating current.

Note: I have nothing to say about how much power factor the circulating current will have. I simply don't know enough on that issue. I am simply talking about the VARs involved for any arbitrary power factor.

-Jon
 
GoldDigger said:
I see what seems to me to be a fundamental problem with the above analysis, namely that the for the unloaded case with the two transformers in parallel the circulating current must be purely resistive. What is it about the loaded case that suddenly makes the circulating current purely reactive?
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Dunno. I'm having a hard time wrapping my head around this concept. 🤔
 
winnie said:
I think I was trying to express that in one of my responses.

To restate differently, we commonly say that loads where the current lags the voltage (inductive loads) 'consume' VARs, and that loads where the current leads the voltage (capacitive loads) 'supply' VARs.

In the case of the circulating currents, the current flows out of the 'top' of one winding, into the 'top' of the other winding, then out of the 'bottom' of the second winding and into the 'bottom' of the first winding. (Yes, the current is alternating....) The point being that the phase angle of the current referenced to one winding is always going to be 180 degrees out of phase as when referenced to the other winding.

This 180 degree phase difference is what means that one winding is supplying power to the circulating current, and one winding is consuming power from the circulating current. Similarly, if one winding is supplying inductive VARs to the circulating current the other winding must be consuming inductive VARs from the circulating current.

Note: I have nothing to say about how much power factor the circulating current will have. I simply don't know enough on that issue. I am simply talking about the VARs involved for any arbitrary power factor.

-Jon
Click to expand...

Does anyone know more about what power factor the circulating current will have?

Also, do both windings heat evenly?
 
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