SOTF protection on Line Differential relay

[Prot123]

Hello All,
Just want to get your view on implementation of SOTF scheme on line diff relays?
I tend to think that being a current based protection no special SOTF(overcurrent threshold based, etc.) needs to be implemented on a line diff. relay. Appreciate your views/experience on this?

 

[sushilksk]

IMO SOTF should be used. It will block AR, which is not required during SOTF.

 

[crshears]

SOTF - simple old transformer fault?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[thermionic1]

SOTF=Switch on to Fault. Likely scenario is that the grounds were left on at the remote end and the line is energized.
Does your line diff relay have distance back up elements? Is it possible you could have a channel failure and still have to energize the line using distance (impedance) elements only?

 

[Prot123]

sushilksk; but i doubt any SOTF scheme put into place would beat line differential in the first place, as SOTF schemes have 1-2 cycle pickup delay.
thermionic1: yeah only if the line is energised with faulty comms and there is a dead short circuit at the yard yielding no polarising voltage for backup distance.

 

[stevenal]

The line differential relays I use have an adjustable time delay between a manual close and automatic reclosing reset. If a fault is sensed during that time, no reclosing occurs.