SOTF calculation

[mabdeltawab]

Usually for Overcurrent relay, we do DFT calculation on current samples to get the 1st Harmonic RMS
then use it in further calculation to get the trip time based on either DTL or IEC/ANSI curves.


What is the difference between SOTF calculation and normal calculation
does the SOTF also based on 1s harmonic RMS ?

 

[cranky108]

Maybe you should explain what you think SOTF is to you.

To me it is Switch-On-To-a-Fault. Which is what happens on a ring, or BAAH scheme when you close onto a fault, and the PT's have not had time to energize.

This most likely happens when someone has grounds on a line, and someone closes a breaker.

 

[Fischstabchen]

Switch Onto Fault is used to trip out quickly without needing directionality. The fault was already determined to be in the segment and if fault current is detected when reclosing, the fault still exist or was not isolated with reclosers and should trip immediately.

 

[mabdeltawab]

@cranky108 @Fischstabchen

I think the difference between SOTF and normal operation is that SOTF mandates instantaneous trip
but normal operation can be instantaneous or based on IDMT


is that correct?

 

[cranky108]

SOTF should be controlled by the breaker positions. First close starts the timer for SOTF to be active.

What does Harmonics have to do with it?