Neher-McGrath "attainment factor"

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morgan3520

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What is the meaning of the "attainment factor" and how do you use Table IX - Comparison of Values of % (AF) for Sinusoidal Los Cycles at 30% Loss Factor form the 1957 Neher-McGrath paper.
 

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The ampacity current I=sqrt(Tc-(Ta+ΔTd)/(Rdc*(1+Yc)*Rca')

Rca'=Ri+qs*Rse+qe*Re'

Re'=0.012*ρe*n'*{log(Dx/De)+LF*log[(4*L/Dx)*F]}

So, in order to calculate Re'[outside thermal resistance] we need to know Dx

the fiction diameter of the last part of the thermal circuit.

If you know the diffusivity of the medium and the thermal cycle duration you may use

formula (45) Dx=1.02*sqrt(α*length of cycle) .If you don’t then use equation (67)

log(Dx/De)=83/n'/ρ*[(1-x)*Rea-x*Rce] where x=(1-AF)/(1-LF).
 
The ampacity current I=sqrt(Tc-(Ta+ΔTd)/(Rdc*(1+Yc)*Rca')

Rca'=Ri+qs*Rse+qe*Re'

Re'=0.012*ρe*n'*{log(Dx/De)+LF*log[(4*L/Dx)*F]}

So, in order to calculate Re'[outside thermal resistance] we need to know Dx

the fiction diameter of the last part of the thermal circuit.

If you know the diffusivity of the medium and the thermal cycle duration you may use

formula (45) Dx=1.02*sqrt(α*length of cycle) .If you don’t then use equation (67)

log(Dx/De)=83/n'/ρ*[(1-x)*Rea-x*Rce] where x=(1-AF)/(1-LF).
Thanks, but what does the "attainment factor" represents?
 
First "attainment factor" it is a name ["what's in a name?" as Shakespeare said :)]
as “ampacity”, for instance, and it was introduced in 1932 [I am not sure because I haven't read this publication] in Calculation of the Electrical Problems of Underground Cables by D.M. Simmons as Neher himself declared, I think.
By the way, IEEE 835/1994 presents an equation of how may be calculated the
diffusivity of the medium α: α=104/(ρe)^0.8 where ρe=Earth thermal resistivity[°C cm/W]
 
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