Bussman Point by Point AIC Calcs

[HYDL]

I've been evaluating the Point by Point method of AIC calcs that is in the Bussman Fuse book and also indicate in other literature. They have calculation for an f factor and an M factor. I'm trying to figure out where they come up with the M factor (the multiplying factor) 1/1+f.

 

[Senselessticker]

Think of "M" as the percent (%) of the available fault current that can travel downstream to a given point on the system.

Where f = some function of length, cable type, voltage, and and available fault current at the "beginning" of a system(in many casees this will be available fault current at the secondary of a transformer)

 

[Senselessticker]

Also note that if all other factors are constant (voltage, available SC, cable type) that M decreases exponentially with cable length.

 

[HYDL]

Thanks for responding. I understand the M being a percentage of available fault. What I'm trying to do is disect these formulas to determine how they were derived. All items in the f formula I can account for, but I'm not sure why they add 1 to the f and then take the inverse.

 

[Senselessticker]

Interesting...now you've got me thinking about it...For now, I'm going to guess that 1/(1+f) is some kind of approximation for:

exp^-f(x)

where f is some real value of function f(x) and x > 0.

OR maybe its some kind of approximation for a summing series. I'll check into later this evening...I'm studying for the FE anyway.

 

[HYDL]

Any more thoughts on the derivation of the point-by-point formulas?

 

[rbulsara]

See thread238-172100 for my opinion.

As for your basic question, ask Bussmann.