Thanks for responding.I haven't used SKM so I can't respond specifically to your question, but it wouldn't make sense for the software to modify %Z pre-emptively. The direction of the presumed tolerance will be based on what type of study you're doing. A short circuit study would want to use -10% Z and an arc flash study would want to use +10% Z, so that value is likely defined when you initiate the specific study.
Your comment in bold...is the value on nameplate ACTUAL test value or factory target value? If this is the case then the tolerance band still applies.I think this is an option in the short circuit settings in SKM. If the transformer is existing, you'll just use the actual impedance from the nameplate, of course, so the software shouldn't do any adjustment in that situation.
Please go to "The nameplate value is an actual test value. It's measured after the transformer is built in every case I've ever encountered. It's part of the routine transformer test prior to shipment, and is a relatively simple measurement. I'd be interested in seeing the statement from Eaton - just out of curiosity.
SKM does also allow specifying a range of utility voltages - again as an option. +/- 5% is a reasonable range - this is allowable normal range in the ANSI standard.
Thanks DavidInteresting. I think his interpretation is incorrect. The ANSI C57 standards he referenced talk about the "specified value" of impedance. When a transformer is ordered and manufactured, it will have a nominal impedance value specified and the standards have nominal impedance values. The ACTUAL impedance as measured by test can vary per the allowed range (generally +/- 7.5%). On older transformer nameplates, the impedance was left blank until the transformer was tested and then the actual value was stamped on the nameplate. I checked Conrad St. Pierre's book on short circuit calculations and he makes no mention of this issue in terms of adjusting nameplate impedances, and I've never heard it explained this way. Perhaps it is different with the very small dry-type transformers, but in my experience there is generally an actual impedance (not nominal) on the nameplate. (This is in the US.)
Thanks for responding.Relatively few general purpose dry type transformers are actually tested. Stock units tyipcally use design values. Custom ordered units often include impedance testing as part of their deliverables.
No, but I am confident every label uses a design value unless a custom test has been ordered and paid for.Thanks for responding.
Rep was a little iffy on the dry types.
So you are confident all padmounts or drytype unit subs label would be a test value?
JimNo, but I am confident every label uses a design value unless a custom test has been ordered and paid for.
Rep implied this was the case for everything...I think you have to be specific about the type of transformer you are talking about. It appears small dry-types are tested to a different standard than pad-mounts or substation transformers.
David…”do whatever….”Do whatever you want, but I don't believe his comments are accurate except for maybe the dry-type transformers. I'm not sure what you mean by "tag", but transformers have a nameplate with the impedance marked.
Yes.Jim
Conversation with my SQ-D rep...
Actual value ONLY provided if a test report is specified.
Xfmer's with a specified test still ship with standard tag that indicates design value, NOT the value from a test.
Every Xfmr IS tested to verify it meets tolerance band, but test value does not get added to factory tag.
Does this match your experience on the topic?