Expertise on theoretical short-circuit current

[PedroUK]

Dear All,

I am new to this forum and I hope that I am going to be able to find a support from an expert in short-circuit current theoretically speaking or someone to assist me in general !

I am working everyday to an international standard IEC60439 (or the new IEC 61439) where it describe the prescriptions for testing LV equipment and especially short-circuit testing where I am seeking help. I have enclosed a document which is from a book where many formulas are explained but not devloped mathematically. It is based upon the standard IEC 60909.
It is only a 2-page document, please read it as my question will be related to this one.
I have demonstrated (after having sweat a lot!) the formula 8.11 OK.
But now I am trying to understand how the peak factor "k" is demonstrated (8.13b and 8.14) but also if the factor k the same as n expressed in the standard IEC 60439?

I do not consider it as homework but if it is, please accept my sincere apology and I will re-enter it in the other forum.

Thanks. PedroUK

 

[PedroUK]

Hello everyone and thank you for reading my question, however receiving no answer, I am wondering if my question is clear?
Please feel free to post a reply for seeking more accurate info if you think some of you are missing important data to respond fully to my demand?

Thanks. Pedro

 

[berkeman]

Dear All,

I am new to this forum and I hope that I am going to be able to find a support from an expert in short-circuit current theoretically speaking or someone to assist me in general !

I am working everyday to an international standard IEC60439 (or the new IEC 61439) where it describe the prescriptions for testing LV equipment and especially short-circuit testing where I am seeking help. I have enclosed a document which is from a book where many formulas are explained but not devloped mathematically. It is based upon the standard IEC 60909.
It is only a 2-page document, please read it as my question will be related to this one.
I have demonstrated (after having sweat a lot!) the formula 8.11 OK.
But now I am trying to understand how the peak factor "k" is demonstrated (8.13b and 8.14) but also if the factor k the same as n expressed in the standard IEC 60439?

I do not consider it as homework but if it is, please accept my sincere apology and I will re-enter it in the other forum.

Thanks. PedroUK

Sorry to be blunt, but you have no EE experience, but are asking how to qualify a product to IEC safety standards? Do you not have some professional EEs at your work?

 

[PedroUK]

Sorry maybe I am explaining myself wrongly. I want to understand how figures from a specific table in the standards IEC 60439 are coming from, not qualify a product to a standard.
I need to understand the maths or physics behind those figures and if they are linked to the factor k that is calculated somewhat.
Perhaps you are right and I should seek info from another source.

 

[PedroUK]

That's all right folks, I found the explanation of my question, I simply forgot some elements to take into consideration. This item can be closed now. Thanks anyway, sort of...

 

[uart]

That's all right folks, I found the explanation of my question, I simply forgot some elements to take into consideration. This item can be closed now. Thanks anyway, sort of...

Hi Pedro. Glad you got it sorted. I'd just read through your attachment before you posted the above and had some info that I was going to give, I'll post it anyway as it still might help.

Equation 8.14 is derived purely empirically. It does not follow analytically or algebraically from 8.13b. Rather 8.13b (well actually it's derivative) is solved numerically for a range of different values of the parameter gamma and the corresponding values of maximum of "k" are so obtained numerically.

Equation 8.14 is then basically just a curve fitting exercise to the above numerical data.

Hope that helps.

 

[PedroUK]

Thanks again for your asssitance I figured it out too late but also I forgot to include sqrt2 to k to obtain the true peaking value when considering a pure inductive load. Hence the maximum peak that I shall consider is around 2.8 or there about.
In real life, when conducting a short-circuit for example at a level of 50kA on LV equipment (switchboard) then the max peak applied on the std IEC60439 is 2.2 for a reason as there are resistive load added to circuit.
Anyway, Thanks again, take care.