Short Cable Length -Fault Contribution
Short Cable Length -Fault Contribution
(OP)
Hi All,
This is my first time and have seen some similar posts like my question. My feeder is 1.5 km from utility and the fault level at that point and my feeder is approx. same and some how my fuse cannot coordinate with their instantenous overcurrent protection.
Could you advise me how a situation like this can be resolved. Is their some kind of methodology to discriminate between same fault level at different location between fuse and instantenous electromechanical relay.
Thanks
This is my first time and have seen some similar posts like my question. My feeder is 1.5 km from utility and the fault level at that point and my feeder is approx. same and some how my fuse cannot coordinate with their instantenous overcurrent protection.
Could you advise me how a situation like this can be resolved. Is their some kind of methodology to discriminate between same fault level at different location between fuse and instantenous electromechanical relay.
Thanks






RE: Short Cable Length -Fault Contribution
RE: Short Cable Length -Fault Contribution
You could ask them to raise their inst setting, but good luck with that.
Alan
RE: Short Cable Length -Fault Contribution
RE: Short Cable Length -Fault Contribution
You may want to make sure that what you are suggesting is also reviewed by some experienced engineer at your end.
Rafiq Bulsara
http://www.srengineersct.com
RE: Short Cable Length -Fault Contribution
Utility is supplying us with a cable feeder and they dont use reclosing on U/G cable feeds. As I recall they have have seprate old individual Inst O/C and TOC Very inverse relay.
As per the suggestion in the post, if they disable their instanteous for my case, it will take their relay atleast .5 secs(relay operating time)+ breaker cycle(air breaker 5-8 cycles) to clear a 12000 A fault on 13.8 kV.
All this time, rest of the customers on the same feeders will see a voltage drop for atleast .5 sec.
1 ) What is your take on this perspective.
2) What does a fault flowing for .5 sec means.
An unrelated question in the same post:
A PILC lead cable or XLPE unarmoured cable; Which one of these cable has a better fauly handling capaciy.
If I look at a TCC, How do I quantify damage on a cable for the fault amplitude and duration. I would appreciate if there is some kind of literaure avaible to know this in detail.
Thanks
RE: Short Cable Length -Fault Contribution
RE: Short Cable Length -Fault Contribution
It is an actual underground cable feeder fed right from the substation breaker and this feeder have other customers as I have been told. Could you kindly reply other part of my (1,2) questions in the above post as well.
Thanks
RE: Short Cable Length -Fault Contribution
There is no single correct answer as to the best approach for coordination philosophy, especially for distribution feeders. The best you can hope for is a compromise that doesn't leave anyone too unhappy.
David Castor
www.cvoes.com
RE: Short Cable Length -Fault Contribution
Could you still advise the practical(historical & statical ) impact of fault current flow for .5 sec and the cable fault capability question in my post.
RE: Short Cable Length -Fault Contribution
RE: Short Cable Length -Fault Contribution
Should I presume that a voltage drop of .5 sec can take down computers motors and lot of other nuisance stuff. As soon as power will be restored after -5 secs, motors will regain inrush current and breakers can trip.
Thanks for your input.
RE: Short Cable Length -Fault Contribution
I agree that you should work with the utility coordination engineer to solve your problem. Have they supplied you with their coordination curves?
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