Continue to Site

Eng-Tips is the largest engineering community on the Internet

Intelligent Work Forums for Engineering Professionals

  • Congratulations Toost on being selected by the Eng-Tips community for having the most helpful posts in the forums last week. Way to Go!

Arc resistance

Status
Not open for further replies.

hhhansen

Electrical
Jan 14, 2004
61
Hi out there
IEC60909 stipulates the principles for short circuit calculations.
It is well known that an arc is generated in case of a short circuit. In our calculation we are neglecting this in order to obtain the maximum short circuit current. But what about the minimum short circuit current to be used for relay settings.
I can not find anything in IEC about requirements for the value of the arc resistance.
Your comments are much welcome.
 
Replies continue below

Recommended for you

Check the 1584. An accepted industry standard for 480V systems the minimum fault current that will be self sustaining is 38% of the BF value.
 
Warrington formula.
The calculation of the arc resistance is an iteractive calculation, if you want to do it manually. Most of short circuit calculation software can manage that.
 
HI,

521AB: warrigton formula is applicable for phase to phase fault. What about the phase to ground fault? Arc resistance calculation for phase to ground fault is not easy to calculate. It depends on line lenght & fault location, tower hight, atmosphere conditions, soil resistance etc.

hhhansen:
Are you talking about arc resistance calculation for indoor swithchgear or for transmission line? If you can use ETAP/CYME/EDSA etc. power system software can takecare of arc flash study for indoor switchgear while you can RUN SHORT CIRCUIT module.
 
Hi
I am referring to short circuit on cables or connection points in industrial applications.
What about IEC requirements rather than IEEE
 
Hi,
Warrigton formula will not work for cable.

I will suggest some calculation for that.

Thanks
 
00123456...

ground faults (overhead lines) are not easy to calculate but not impossible. The earthing tower resistance is known, and the arc is calculated with the Warrington formula.
Clearly the Warrington formula contains the phisical aspects of the overhead line, and also it is possible to consider the wind effect.
But we are talking about cables, so forget about it.
I don't have the answer.
I would say that it is more important the estimation of the equivalent source impedance then the maximum arc resistance.
In the cables, there are no trees growing ( :) ), I have always "seen" cable faults with a very small fault resistance (disturbance recorder analysis), but if somebody has some figures, I am also interested in knowing them.
 
Status
Not open for further replies.

Part and Inventory Search

Sponsor