Understanding Arc Flash Fault Current Differences from DAPPER Results

Overview

Arc Flash Evaluation may display bolted and arcing fault currents that differ from the DAPPER short-circuit result. This is expected because Arc Flash Evaluation selects the calculation case that produces the largest Incident Energy (IE), rather than simply displaying the DAPPER calculated fault current.

Requirements

• SKM PTW v11.0.1.1 or a project using Arc Flash Evaluation and DAPPER short-circuit studies.

How Arc Flash Evaluation Determines the Result

1. Arc Flash performs calculations using both Imax and Imin.
2. It determines which calculation produces the largest Incident Energy.
3. It displays the arc flash results from that calculation case.
4. The selected case can therefore have a lower fault current than the DAPPER result.

Example

For a bus where DAPPER calculates a fault current of 14.08 kA, Arc Flash Evaluation may display:

• Bolted fault current: 12.32 kA
• Arcing fault current: 7.10 kA
• Trip time: 0.060 s

The lower value can be correct when the Imin calculation produces the largest Incident Energy. The PPE Notes column identifies which calculation is being used. In the reported example, Imin produced 0.92 cal/cm², compared with 0.87 cal/cm² for Imax, so the Imin results were displayed.

Rerunning After Input Changes

After changing an Arc Flash input, such as Equipment Type or Electrode Configuration, click Rerun Study to recalculate the Arc Flash results. Changing a parameter may make the displayed values appear to match DAPPER temporarily, but the Arc Flash result is still based on the calculation case producing the largest Incident Energy.