Relay Settings for Ring Bus 1

[Mbrooke]

Ok, here is what I want to see: Both breakers open for a fault. 15 seconds latter one breaker makes an auto re-close attempt. Said breaker trips. After a quick delay the line terminal MOD opens. Once the position switches indicate the mod is open the breaker closes back in and then its companion for a line fault. For a bus section fault the breaker re-opens and the relay locks out.


How do I go about accomplishing this? SEL 421 relays.

 

[davidbeach]

Two shot reclosing. Free form logic that opens the MOD for “TRIP AND SH1”.

 

[Mbrooke]

Should I pause the 79 cycle waiting for the MOD to open or just let it cycle through on time delay?

 

[davidbeach]

Just use a long enough open interval. On our lines that have MODs that respond to line operations we use 15 second open intervals, but tighten that up to 5 seconds when all automatic response is by circuit switchers.

 

[Mbrooke]

Easier than I thought.

Have you ever had a sluggish MOD inadvertently open under load?

 

[davidbeach]

Not that I can recall, but we have had cases where an MOD has closed to make a fault because the fault happened after the MOD was told to close. That probably wouldn't be an issue in a station with the configuration you describe, but we have automatic sectionalizing stations that are controlled by presence or absence of line voltage. Line comes hot, stays hot long enough for the close command and then the fault restrikes (tree during in wind storm or some such) while the MOD is closing. No way to tell it to stop closing.

 

[Mbrooke]

Good to know. Not really an issue here.

Curiosity: does the MOD survive closing into the fault?

 

[davidbeach]

Generally don't have MODs at locations with high fault current, but every time we're aware of it happening we send a maintenance crew out to give it a check. I don't know what they might typically find.

 

[DTR2011]

We use a scheme where the MODs open circuit is wired in series with the two breakers 52b contacts to prevent opening under load.

 

[bacon4life]

We have MODs halfway down a line that open similarly to what you want to do. We open the MODs based on loss of voltage. In the SEL421 reclosing logic, we use a 15 second timer and check for dead line. The only times we have had sluggish MODs is when thieves steal the batteries from the remote site.