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1
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crjohnson
Electrical
- Mar 31, 2017
- 3
Hi Folks,
I think I may have found an inconsistency in IEEE 242-2001 between the equations Section 9.5.2.4 and Table 9-6.
I hope that I am making a mistake somewhere, and y'all will be able to help point out my error.
Edit: I believe if you follow just the equation for any value of K other than 1, the equation results are way off. For values of k<1, you could overestimate the amount of current the cables could handle by a factor of 2 or more.
Based on the standard, values in table 9-6 are calculated based on the equation shown in 9.5.2.4:
However, if you plug in the values as indicated the results returned do not equal that of the table.
For example, take first line of table 9-6 calculated for EPR-XLP with Te=130, Tn=90,and To=40
From the table:
But, if you change the equation to divide by k instead of multiply by k then it appears to work.
From Equation as corrected:
Does the corrected equation work for y'all?
Did I miss somewhere in the section where is says the inverse of K should be used?
I attached my spreadsheet where I ran my tests.
Thanks,
Chris
I think I may have found an inconsistency in IEEE 242-2001 between the equations Section 9.5.2.4 and Table 9-6.
I hope that I am making a mistake somewhere, and y'all will be able to help point out my error.
Edit: I believe if you follow just the equation for any value of K other than 1, the equation results are way off. For values of k<1, you could overestimate the amount of current the cables could handle by a factor of 2 or more.
Based on the standard, values in table 9-6 are calculated based on the equation shown in 9.5.2.4:
Ie/In % = SQRT(((Te-To)/(Tn-To)-e(-Θ*K))/(1-e(-Θ*K))*((230+Tn)/(230+Te)))*100
Where:Ie is emergency operating current rating,
In is normal current rating,
Te is conductor emergency operating temperature,
Tn is conductor normal operating temperature,
To is ambient temperature,
K is a constant, dependent on cable size and installation type (see Table 9-5 in IEEE 242-2001),
230 is zero-resistance temperature value (234 for copper, 228 for aluminum),
e is base for natural logarithms.
In is normal current rating,
Te is conductor emergency operating temperature,
Tn is conductor normal operating temperature,
To is ambient temperature,
K is a constant, dependent on cable size and installation type (see Table 9-5 in IEEE 242-2001),
230 is zero-resistance temperature value (234 for copper, 228 for aluminum),
e is base for natural logarithms.
However, if you plug in the values as indicated the results returned do not equal that of the table.
For example, take first line of table 9-6 calculated for EPR-XLP with Te=130, Tn=90,and To=40
From the table:
k=0.5, %=1136
k=1.0, %=1602
k=1.5, %=1963
k=2.5, %=2533
From Equation as written:k=1.0, %=1602
k=1.5, %=1963
k=2.5, %=2533
k=0.5, %=2265.49
k=1.0, %=1603.885
k=1.5, %=1311.5
k=2.5, %=1018.061
k=1.0, %=1603.885
k=1.5, %=1311.5
k=2.5, %=1018.061
But, if you change the equation to divide by k instead of multiply by k then it appears to work.
Ie/In % = SQRT(((Te-To)/(Tn-To)-e(-Θ/K))/(1-e(-Θ/K))*((230+Tn)/(230+Te)))*100
From Equation as corrected:
k=0.5, %=1136.859
k=1.0, %=1603.885
k=1.5, %=1962.765
k=2.5, %=2532.281
k=1.0, %=1603.885
k=1.5, %=1962.765
k=2.5, %=2532.281
Does the corrected equation work for y'all?
Did I miss somewhere in the section where is says the inverse of K should be used?
I attached my spreadsheet where I ran my tests.
Thanks,
Chris