SKM TCC Curve

[steve66]

I know what the transformer inrush point is, and I see a marker for the transformer full load current. But do the other 2 or 3 lines for the transformer mean?

 

[charlie b]

They represent the "transformer damage curve." You want the protective device upstream of the transformer to be below this curve. I don't know where PD-006 and PD-008 appear on the one-line, but neither is coordinated with the transformer damage curve.

 

[steve66]

Thanks, Charlie. That's what I suspected, but I'm not sure why there are two lines for this, and why one branches off. (Maybe one is a lower limit and the other is the upper limit?)

PD-006 and PD-008 are two possible choices for the transformer primary protection.

Is it acceptable and/or common to let the circuit breaker on the transformer secondary protect the transformer? Like this:

 

[ron]

Look about 2/3rds of the way down this link
http://www.skm.com/Equipment%20Damage%20Curves%20Transformers.shtml

For primary protection you want an E rated fuse.

 

[steve66]

Thanks Ron. My head is spinning from that link.

PD-0010 is the curve for an E rated fuse, but the current plan is to have adjustable HV relays protecting the transformers and cables. However, I am assuming that the relays can be programmed to mimic an E rated fuse.

Steve

 

[coulter]

Ron -
That's an excellent link.

Thank you

carl