No ac Decrement (NACD)

[wbd]

Hello,

Could anyone provide the name and number of the IEEE document that defines NACD. I've been through a number of books I have and have been searching the hardcopy of the IEEE C37 Book but have not had any success. I think if I had it on a pdf I could do a search and find it. Personally, I don't find the IEEE C37 book to be very user friendly.

Thank You

 

[dpc]

I'm pretty sure it is in ANSI C37.010, but I don't have a copy here at home. I'll check when I get in the office later today.

 

[dpc]

Our copy of C37 seems to have grown legs, but I checked Conrad St. Pierre's book and he references C37.010 when discussing definitions of Local, Remote and NACD.

NACD is a ratio of the non-decaying ac current to the total short circuit current, per CSP's book.

 

[JensenDrive]

Here is the closest to a definition of NACD that I can find in C37.010. The document uses the term in several subsequent discussions, and assumes the concept is understood from this:

A.4 Derivation of E /X multipliers
Figure A.5 shows the relationship of fault current (Iasym/Isym)nacd (the subscript nacd indicates that there is
assumed to be no ac decrement) as a function of X/R for various contact parting times. This family of curves,
which considers only the decay of the dc component of fault current, forms the basis of....

 

[wbd]

If I'm understanding this correctly, then there must be a typo in Conrad's book where he references NACD as non-decaying ac current(Isym) to total fault current (Iasym)whereas C37 has it as Iasym/Isym.

 

[dpc]

I'd have to assume the definition in ANSI C37.010 is "definitive".