Are we talking about an ungrounded power system? If so, then a transient over-voltage due to an intermittent ground fault would be a likely culprit.. need more information regarding the power system and fault that occurred.
There are more things to consider before choosing an "arbitrary" pickup level. For starters, hopefully this transformer does not feed any single phase load or load that is unbalanced in any way?
Your NGR is rated for 400 Amps, but only momentarily-- ask the manufacturer for a damage curve of...
One quick question: does this transformer feed any single phase loads? Is there proper zero sequence removal from the wye side winding for any SLG faults or heavy loads that may arise on a single phase? This zero sequence removal can be done through either settings or ct wiring.
One other question: high impedance differential or low impedance differential?
Either way, you will have some serious issues with CT lead lengths of over half a mile... Like the earlier post said: I think you need more differential zones. If you need maximum selectivity (which is best...
Direct wiring a trip to the alarm contact on an SEL (or any relay for that matter) is a bad idea. As mentioned before, the alarm contact will assert for reasons other than simply relay failure. If it were me, I would wire the relay failure alarm b-form contact into another device (SCADA or any...
I do the majority of my modeling work in ETAP, and the new version (11) has a module for modeling PV arrays. However, I have zero experience with it.... Just letting you know!
Here's my 2 cents.... Back in the day you when you were working as a field tech or whatever, you were probably around new substations that were just energized so had very little, if any, load current. Nowadays, you're an office man, going to existing substations operating at full capacity...
If you decide to reclose, you might look into one of the modern transformer protective relays will monitor through faults and give you lots of useful information on transformer life, etc. Unfortunately you usually have to get the expensive model to add these features though...
