Frequent vs. Infrequent Xfmr Damage Curves

[lielec11]

I keep coming across references to frequent vs infrequent damage curves for transformers. SKM refers to the transformer TCC curves as "primary side thermal limit" and "secondary side thermal limit", with an additional two legs at the bottom referred to as primary and secondary damage curves. Can someone clarify what the frequent and infrequent curves are? Are they the bottom legs, if so, which is which?

 

[Bugman1400]

It has to do with the frequency of faults downstream and that effect on the life span of the xfmr. The frequent curve is always used.

 

[lielec11]

It has to do with the frequency of faults downstream and that effect on the life span of the xfmr. The frequent curve is always used.

I get that much, I am trying to figure out which curve is which. I guess my question wasn't clear enough so I apologize.

If you're looking at a standard transformer TCC, which curve is the frequent and which is the infrequent? There are typically a "left" and "right" limit to the damage curve.

 

[kingpb]

I get that much, I am trying to figure out which curve is which. I guess my question wasn't clear enough so I apologize.

If you're looking at a standard transformer TCC, which curve is the frequent and which is the infrequent? There are typically a "left" and "right" limit to the damage curve.

This should help:

 

[lielec11]

kingpb that's just wanted I needed, thank you!