Short Circuit Value

[sak3281]

I have carried out ANSI 30cycle Short Circuit Study in SKM but the Values of ANSI_30cycle_3P & SLG is 20A & 12A respectively at 13.8kV. The utility is rated as 500MVA.

What might be the problem.Why the Value is so small? I cannot do the settings for the relays unless I rectify this.

 

[EddyWirbelstrom]

More information is required. One-Line Diagram ?
Is the Utility 3 phase short-circuit contribtuion of 500 MVA at 13.8kV ? 3P SC = 500 MVA / ( sqrt(3*13800 ) = 20.92kA

 

[rbulsara]

Look more closely at the units of all data that you put in as well as output.

Rafiq Bulsara

http://www.srengineersct.com

 

[sak3281]

In the attach link you can see that the value of I30cycSLG is 2231.75A. The FLA of Chiller#1 is 873.6A at 380V with starting inrush of 5.88 x FLA.

Now the starting inrush for Chiller#1 is much higher then the minimum fault current (I30cycSLG i.e. 2231.75), so I want to now at how many times of FLA of Chiller, the Instantaneous Protection shall be set at???

 

[rbulsara]

In the attachment the 3 phase fault is 60kA and only SLG is 2.2kA.

What does chiller starting kA has to do with SLG fault current? Motor starting will not be seen by the ground fault element.

As for actual settings, it depends on your objectives. Low as possible but high enough to coordinate and avoid nuisance trips.





Rafiq Bulsara

http://www.srengineersct.com