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IratelyBlank posted:I'm an EE student (although early in the curriculum) and is there a reason that it is always voltage being described when people talk about power lines and etc and not current? I have a hard time putting a "danger value" on a piece of equipment or whatever without both a current and a voltage, but that may be something I haven't been exposed to yet? Equipment voltage ratings are standardised across the whole power distribution system. Current ratings aren't. At the transmission and distribution levels there are a range of different conductors used with widely varying current capacities but usually* the same voltage rating. The reason is that more current capacity means more aluminium or copper in the wires with bigger towers or poles to support the strain and more land required. Or bigger cables and larger ducts. Even in a substation stuff at the same voltage is rated to different fault current capacities. *Things get operated at lower than their design voltage sometimes.
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Sep 9, 2011 08:59
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| # ¿ May 6, 2024 21:43 |
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http://entergy-neworleans.com/content/superbowl/130202_Report.pdf I wonder what other undocumented features S&C relays have. Yeesh.
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Mar 29, 2013 04:10
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My favourite part of the report is at the end where the author references a list of email chains because email chains are where a protection engineer lives and dies.
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Mar 29, 2013 07:18
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Pvt Dancer posted:e: Now I see why they're blaming S&C. When they put these weird rear end relays in they better set it to the right value, it only depends on fuse size. Although it is primarily S&C's fault because the manual didn't explain anything, the utility is also to blame because relying on a blocking circuit to prevent load encroachment trips when you aren't forced to to is a bad idea. An undocumented blocking failure mode from the factory isn't usual but leave an electromechanical/electronic relay in service for 40 years of nuisance pickups and eventually the thing might either spuriously trip or not pickup at all. Load blocking to prevent spurious trips does make sense for distance protection relays where you're sending hundreds of MVA down a long transmission line and the load impedance is low enough that it can creep into backup distance zones. In that situation the relay uses the power factor of the fault to discriminate. Fault blocking for coordination when paired with distance protection is occasionally the reason for gigantic blackouts because you're relying on the blocking signal to get to all upstream protection devices and slow them down. If you have the distance protection at transmission substations backing up not just the adjacent subs but ones further away and the person coming up with the scheme misses a weird failure mode or the network gets reconfigured without a proper review you can trip gigantic amounts of load.
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Mar 30, 2013 05:00
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TheFargate posted:Do you guys not have a set up for work on your reclosers? I know for the line guys, when they need to work, we switch reclosers to instant trip and no reclose. Not 100% sure if we do that for guys closing manual switches. Live line work should have fast trips on your reclosers with reclose disabled, but closing an ABS doesn't usually require it. That engineer who wanted to keep switching after a near fatality switch failure needs to be reported to the local board or safety authority that is not cool. Disabling SEF to parallel lines can be standard, but turning off all earth fault protection is nuts. edit: I hope someone at your company is investigating this, because if that model of switch failed and you have a lot of them its a matter of time before it happens to someone else. slorb fucked around with this message at 12:36 on Oct 26, 2015 |
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Oct 26, 2015 12:32
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angryrobots posted:
If you're paralleling radial feeders with open delta regulators on them you will have an induced loop of zero sequence current which will often trip the sensitive earth fault protection unless the regulators are locked at neutral tap. Another situation that can trip recloser SEF is a bad (resistive) connection on one phase of a non-ganged switch close leading to unbalanced load on that phase. I believe this is the one you're disabling the recloser EF for. If your protection guys know what they're doing you shouldn't have all your recloser EF protection pick ups low enough to require disabling it entirely on the recloser though, the whole point of SEF is its set low and slow so you have it as a backup under normal operation. I hope the button you're talking about just disables SEF. slorb fucked around with this message at 04:43 on Oct 27, 2015 |
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Oct 27, 2015 04:40
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| # ¿ May 6, 2024 21:43 |
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angryrobots posted:OK so a clarification. I asked our one guy (yes we have over 4k miles of distribution and 30k customers, with the absolute bare minimum of employees but I digress) and while he did not use the term sensitive earth fault protection, it may be exactly that. Huge props to that guy who does all your protection, doing protection work on your own is scary poo poo. Yeah if you're closing in one phase at a time to a parallel feeder (especially one fed from a remote substation) and there's a big enough difference in impedance to the substation(s) on the different feeders you'll get unbalance current that will trip the feeder on earth/ground fault. If you're just disabling the slow extra sensitive earth fault curve that makes sense. The reason I was concerned is if you're disabling all residual (earth fault / ground fault) protection on the recloser on a 12kV feeder it is unlikely your phase fault OC setting can be low enough to pick up on high impedance ground faults like conductors hitting a tree or a line down on crap sandy soil unless its a very lightly loaded line.
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Oct 28, 2015 09:03
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