Relcosing logic for 311C
Relcosing logic for 311C
(OP)
Starting this thread as not de-rail another one. How do you guys set the reclose logic for two terminal 69 and 115kv lines with non communicating, non PLC relays? The desired outcome is to have only one relay do a single reclose attempt after 30 seconds, and once the line holds for 20 seconds have the other relay close its breaker after a sync check. Ie, have the remote relay not reclose but also not lockout.






RE: Relcosing logic for 311C
You can get fancier and do a stall on dead line and have a 20 second reclose at the second end.
You can get terminally fancy and watch for the line to come hot, then drop out again, and then drive to lockout. That will fail you now and then for various reasons.
We've gone to a fast end-slow end approach, but the slow end is only 30 cycles slower than the fast end. We've been using SOTF longer than we've been doing the fast-slow, so if the fast end closes into a fault, it will be open again long before the 30 cycles has elapsed.
We do, however, have longer "waits" when the slow end is at a plant, we may wait 15 seconds in that case to make sure the line is going to hold.
If you're going to have 20 seconds between recloses, you probably want a reclose reset time longer than that, perhaps 30 seconds.
RE: Relcosing logic for 311C
Will anything be gained or have to be changed in settings by having a set of 3 phase VTs on the line and a single VS on the bus? This is a straight (simple) bus system.
Is there any benefit of having the relay drive to lockout vs having it so the relay will automatically come back in once the line is energized say several hours latter after repair?
One possible issue I see arising here is that with a single VS and a bolted B phase fault or a bolted 3 phase fault with 3 phase VTs that the voltage may not rise high enough to assert drive to lockout. I am guessing this is what you were referring to regarding failing?
Makes sense and I will keep this in mind.
RE: Relcosing logic for 311C
We try to limit automatic operations to the period immediately following the fault. Once people might have arrived at the station we don't want an auto reclose well after the fact. But if you've got a really remote station with no SCADA control it might be desirable to have it auto close once the line comes hot.
RE: Relcosing logic for 311C
I agree with david, that you want a timer to allow the second reclose breaker to expire if the line does not come and stay hot.
RE: Relcosing logic for 311C
Automatically restoring the second terminal via sync check might be worthwhile if it saves operators/dispatchers significant time during restoration. Delayed automatic reclosing of the first terminal into a dead line seems risky.
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
@Cranky108, I use SOTF even on bus mounted VTs in that a 3 phase fault near the substation can also produce deeply depressed voltages.
RE: Relcosing logic for 311C
By risky delayed reclosing, I was referring to:
RE: Relcosing logic for 311C
But your point is far from invalid, a fast reclose is a good idea in those cases.
RE: Relcosing logic for 311C
SOTF - if the protection voltage is in front of the relay, aka on the line, then the SOTF trip elements must include non-directional overcurrent elements. If the protection voltage is behind the relay, SOTF can be done with just the zone 2 distance pickups. I see no reason not to include SOTF on transmission; distribution is sort of the opposite where instantaneous tripping is turned off following the first reclose. But on transmission there's no tapped fuses that you want to blow, so trip as quickly as possible and minimize the disturbance to the rest of the customers.
RE: Relcosing logic for 311C
None of that here over 35kv, but in such a case it would certainly make sense and I hear you.
Any idea what these typical over current values should be set at? Would there be an flaws using zone 2 for line VTs?
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
For SOTF (or line test, as we call it) we use an overcurrent element AND'd with an undervoltage element.
The overcurrent element is typically set to be the smaller of 50% of the minimum TPF for the protected line, or 10A secondary.
We use 0.3pu for the undervoltage pickup, for more than 2 seconds.
Mark
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
Marks1080: Thank you- excellent! I never considered adding voltage to that over current, but I will take that into consideration.
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
If you are using OC only (with voltage supervision - which I would recommend) that pickup will be too high.
50% minimum TPH fault is a good level to use (or 10A secondary - whichever is less) for OC line test. You want to consider the system configuration for when you actually want line-test to work. The line is dead, and one terminal gets closed in first. That's the line test scenario. You could be testing because someone left grounds on the line (maybe the most common reason for this), but also consider other types of possible faults that could happen while a line is dead.
I believe our standard voltage setting for supervision of the OC element is 0.3 pu, probably based on a 500kV application. You may want to tweak that depending on your set-up, but I think 0.3 should be safe for most applications.
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
If you are expecting unbalanced loading, then setting the ground higher is alright.
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
So: I apologize for my ignorance, but what is SOTF an abbreviation for in the Protection and Control world?
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
but what is "POCO" ????
RE: Relcosing logic for 311C
Sorry for all the jargon. I tend to over use it at times lol.
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Relcosing logic for 311C
The issue is not that most of the requirements are a concern, it's the paperwork and documentation, that required us to hire so many lawyers who don't even understand the requirements.
Also the auditors who have no idea what they are auditing. They just want to see the paperwork.
It's sort of like a federal government takeover of the utilities.
RE: Relcosing logic for 311C
I am wondering: are there any US/Mexico tie lines that will need to be routed through a "power wall" in some manner?
CR
"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]
RE: Relcosing logic for 311C
Regardless what people think, places like India are where talent can spread its wings.
RE: Relcosing logic for 311C
There are lines into Baja Mexico, likely they are taller than the wall of Southern Cal/Mexico border.
RE: Relcosing logic for 311C
But with the way things are going we might not even be exchanging power with Mexico.
RE: Relcosing logic for 311C
The connections with Mexico are not that major, in that it only includes Baja Mexico, and not the whole country.
I was not even aware they use 60 Hz until a number of years ago.
RE: Relcosing logic for 311C
If I am not mistaken Mexico used to be 50Hz more than half a century ago but was converted over, at least that is what I have heard.
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
https://www.youtube.com/watch?v=RV3hEKLNm74
Although to be honest I prefer the sound of 50Hz to 60Hz.
RE: Relcosing logic for 311C
Does anyone know how to set the logic such that re-closing is blocked for zone 2 and zone 3 faults but proceeds as normal for a zone 1? This would hold for both positive sequence MHO and ground quad elements in regard to their respective zones.
I checked the manual but it only mentions 3 phase faults as follows:
RE: Relcosing logic for 311C
First set the zone 1 common timer to 0, not OFF. Then 79DTL would be TRIP * !Z1T.
I've seen too many instances where relays over trip for what ever reason to not want every distance element trip to reclose. But this is far from the first time I've seen the idea of only reclosing on zone 1, so maybe I'm missing out on something.
What about faults toward the remote end of the line for which zone 1 never picked up? How well do all of your zone 3 (probably really zone 4 if you're using SEL relays) elements coordinate? That is, how well do they continue to coordinate as tripping progresses? What looks to coordinate before the first trip may not, or conversely, what looks not to coordinate at all prior to the first trip actually coordinates perfectly well afterward. Personally, I'd be more worried about not getting the reclose on an over trip than having a zone 4 operate twice.
RE: Relcosing logic for 311C
Oh, that is easy! :)
In a system with none communicating protection relays a Zone 2 pickup can either be a line fault on the far end or a bus fault with a simultaneous stuck breaker at the receiving station. If the latter it is generally a good idea not to reclose onto a faulted bus. Now with communicating relays a failed breaker during a bus fault can send over a DTT to the sending station preventing a re-close. In such a system (with communication) relcosing one both zone 1 and zone 2 can be done without worry.
I am sure there are other reasons out there, but in my case this is the primary driver not to reclose on zone 2.
In such a system both 311C (or both 421) relays have a single re-close enabled on Zone 1. Which ever relay picked up zone 1 will reclose 15 or 30 seconds latter, and if the re-close is successful the relay on the other end which picked up on zone 2 will re-close after a synch check (hot line, hot bus). If both ends pickup on zone 1, then one end will reclose after 15 seconds and then the other after 30 seconds regardless if the first relay was successful or not at re-closing.
I know this sounds messy, but in a none communicating system its often a compromise.
In my world if a a relay trips on zone 3 (zone 4) this would indicate a serious problem such failed relaying at a remote substation. There of course could be a high Z fault out on the line, but the concern is generally not great enough to consider reclose.
Of course zone 3 trips can occur if a line is heavily loaded, however this would be mitigated via load shedding or generation re-dispatch before zone 3 elements (or over current elements) pick up.
Generally speaking a system which can tolerate a 30 second reclose delay via 3 pole tripping (vs needing single pole high speed auto reclosing) indicates a strong system with many other paths in the flow-gate. Thus biasing a system for dependability rather than security presents no major risk to losing load and is considered good practice. A line or element failing to trip, or a bus fault reclose, take more concern.
Though I do hear you, and your concerns are valid none the less.
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
A hypothetical what if... does not mean I will do it that way. What if I just kept things close to the factory settings so the speak, giving both relays a single reclose attempt (15 sec for one 30 for the other) and not bothering to to stop reclose on zone 2 and zone 3?
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
Here is one example of steaming before flashing over:
https://www.youtube.com/watch?v=pNsUDmlG6js
RE: Relcosing logic for 311C
RE: Relcosing logic for 311C
Still a tad confused though- I am able to get zone 2 and zone 3 to initiate drive-to-lockout, however is there anyway to set up an timed 79DTL expiration or reset for when the line comes back live?