Primary fuse and xfmr damage curve
Primary fuse and xfmr damage curve
(OP)
in one of the S&C publications , it is referred to an article from " J. R. Dunki-Jacobs " The effects of Arcing ground faults on low-voltage system design" which shows the secondary switchboard on 480/277Y volt circuit can have magnitudes as low as 40% of the maximum available L-G fault current.
Then it’s shown for a Z=8% xfrm this can be as low as 290% and this is considered as the minimum safe point for fuse curve to intersect the xfmr short-time curve.
I can not find the article in IEEE website as it was printed in1972.
1) Does anybody know a similar article or literature that I can find values for say 600V switchboard?
2) I have also found that there is no difference between the 1000KVA and 1500KVA or 2000KVA xfmr curves, am I making mistakes somewhere, SKM shows same curve for all three!
Then it’s shown for a Z=8% xfrm this can be as low as 290% and this is considered as the minimum safe point for fuse curve to intersect the xfmr short-time curve.
I can not find the article in IEEE website as it was printed in1972.
1) Does anybody know a similar article or literature that I can find values for say 600V switchboard?
2) I have also found that there is no difference between the 1000KVA and 1500KVA or 2000KVA xfmr curves, am I making mistakes somewhere, SKM shows same curve for all three!






RE: Primary fuse and xfmr damage curve
RE: Primary fuse and xfmr damage curve
It is true that arcing faults are generally considered to be around 40% of available short circuit current. The current standards, IEEE 1584 and NFPA 70E, considers it to be 38% for its calculaiton methods. Do not confuse this with sizing of fuse sizing for transformer protection. This is even true for any type of overcurrent protection.
RE: Primary fuse and xfmr damage curve
That 38% referes to the min current that the arc will be self sustaining, I think that is only for 480V systems.
RE: Primary fuse and xfmr damage curve
When it comes to the ground fault protection, you have to compensate for the delta-y arrangement. The primary fuse will see 58% of the secondary winding current(per-unit). You have to shift the transformer through-fault curve by 58% to the left and check your fuse curve against it. Hope this answers some of your questions.