Bung
Electrical
- Feb 10, 2002
- 428
We use sensitive earth fault protection set at around 8A pickup on our 400A (CT primary) 11kV feeders supplying overhead lines. The idea is to detect and trip downed conductors. The time setting is 10 second definite time.
The problem is that in the past the relays used have an instantaneous reset characteristic. The advent of digital relays means that we know more about what faults rreally look like. The recordings from an actual fault showed us that a downed conductor at the side of a road (about a metre of conductor lying on dry sand) resulted in a fair bit of arcing, the conductor jumped around a bit, but the fault current was being interrupted before the full 10 sec time-out was reached. The feeder was eventually tripped by remote SCADA ops from the control room. The fault current was not enough for the standard e/f relay to pick up.
Has anybody any experience with using a slow reset function on SEF relays? This will extend the total time to trip where on-again off-again arcing occurs, but is better than no trip at all. What reset function was used (linear, fixed time etc?), problems encountered etc.
(BTW, conductors on sand make these really cool little glass tubes! (and no, don't try it at home, folks))
thanx
Bung
The problem is that in the past the relays used have an instantaneous reset characteristic. The advent of digital relays means that we know more about what faults rreally look like. The recordings from an actual fault showed us that a downed conductor at the side of a road (about a metre of conductor lying on dry sand) resulted in a fair bit of arcing, the conductor jumped around a bit, but the fault current was being interrupted before the full 10 sec time-out was reached. The feeder was eventually tripped by remote SCADA ops from the control room. The fault current was not enough for the standard e/f relay to pick up.
Has anybody any experience with using a slow reset function on SEF relays? This will extend the total time to trip where on-again off-again arcing occurs, but is better than no trip at all. What reset function was used (linear, fixed time etc?), problems encountered etc.
(BTW, conductors on sand make these really cool little glass tubes! (and no, don't try it at home, folks))
thanx
Bung