breaker fail philosophy 240kV 1

[Sn00ze]

hello,

i have am beginnign design on a 240kV substation connecting a single line to the grid.

the sub will receive 10 x 35kV feeders from wind turbines. but i am wondering how people handle breaker fail ?

I have a bus protection, 240kV (main/line) protection and the feeder protections. Should the bus protection and the 240kV breaker have the BF alone? or hsould the feeders have BF also?

 

[davidbeach]

With breaker failure logic an integral part of every decent relay these days there's no reason not to provide breaker failure protection for every breaker.

 

[DTR2011]

I would assume that the 240 kV BF philosophy would be dictated by the interconnecting utility. At that voltage I presume the utility would require both Transfer Trip Send (your BF to them) & TT Receive (BF trip from them) via some kind of communications channel. This is often complementary to the regular line protection channel, via power line carrier, fiber or other.

I've seen all kinds of different implementations of BF. If you have 35kV Bus Diff and an associated Lock Out Relay, your BF relays can trip the 86B. BF Relaying can be implemented via dedicated BF relays, or have the function built into the digital relay logic. Some prefer a dedicated 86BF LOR. Some may use a digital low impedance bus relay with multiple trip contacts. I've heard of BF implementation via IEC 68150 as well, but it's not popular in my region.

I've seen 35kV VCB's that have an integral high speed grounding switch that was part of the feeder BF scheme. Other than clearing the 35kV bus, unless you have a communications channel to the WTG CB trip there is not much else you can do at that level. As an aside, I've seen the catastrophic results of the VCB integral ground failing while in service.

 

[marks1080]

It would be strange to see any of those breakers without breaker fail in my opinion. As David was saying, it's basically free to deploy so why wouldn't you?

 

[Sn00ze]

Yes every breaker has BF, but should every protection employ it?

Example (after speaking with my settings engineer): we agreed to remove it from the TX protection and bus protection (as this works via a summation CCT so it is unable to differentiate the fault/CT). Left it on the feeder protection iwth a time delay and for sure on the Line breaker (240kV).

do you agree?

 

[DTR2011]

"Yes every breaker has BF, but should every protection employ it?"

I would say yes. Any trip should initiate BF (timer). If you have dedicated BF relay, every relay initiates BF relay. If BF is integral to other protection every trip should internally start the BF timer and trip LOR after BF time (+current).

 

[Mbrooke]

Do not remove fail from a transformer. That is the absolute LAST place I would do so because unlike a transmission line breaker failure which could be picked up by remote zone 2 or zone 3, a transformer fault may not produce enough current to trigger other relays. The internal fault could heat the oil to the point of boiling and catching fire doing obscene damage. The cost, down time, and image damage would justify any BF many times over even if a rare event.


On the other hand a failed 35kv feeder breaker could easily pickup transformer over current protection if set to do so.


BF on the 240kv bus bar. What type of bus topology are you using? Straight; sectionlized; single breaker double bus; ring bus; breaker-and-a-half? If using anything outside of straight bus its wise to have breaker failure initiated for a bus fault. Reason being that if a breaker jammed when clearing a bus fault, its possible to clear more than the one bus section or even possible to clear all 240kv incoming lines. Which in of itself may not be a big issue, but if you are using ring bus or breaker-and-a-half, chances are that design was selected specifically with intent to keep as many things possible in service during a bus fault or breaker failure. But even with straight bus, you have to ask yourself- are you ok with a remote terminal reclosing into a bus fault if zone 2 and 3 re-close?


Also to consider: without BF is the system ok with waiting for none communications assisted (delayed) tripping?

Overall in most cases I would not loose sleep over not having busbar protection in a none bulk substation, but I would very much worry about not having it on the transformers.


Breaker failure logic comes pre-intergrated into most new relays, so implementing it very easy. Something as simple as having a "master trip" auxiliary relay on each bay mimick board and routing the output of each relay's BF to trip the associated aux relays can make a huge difference. People here mention lockout relays, but honestly, you don't need them if you have virtual lockout relays.

 

[Mbrooke]

And also just a few things regarding BF:

1. When protecting a transformer I would use OR instead of AND logic, meaning a closed 52A OR current detectors will intiate BF. Not both- reason being that as mentioned above a trafo fault may not produce substantial currents.

2. Giving credit to those here on this forum- if your breaker locks out due to low SF6, have the relaying automatically arm BF via an SF6 lockout input. When a fault occurs, BF outputs are automatically initiated instead of waiting for 8 cycles while using typical criteria.


Do you have a single line of this substation by chance?

 

[marks1080]

Breaker Fail is it's own protection, not a protection to be deployed by other protections. Breaker fail should be initiated every time a breaker is called to trip. Mbrook I'm a little confused with your comment on 52A or current detectors to initiate BF, can you clarify? We have use 3 BF times, 62a,b and c. One is mechanical failure (using adv. 52/a), one is an electrical failure (using o/c function) and the last is just time delay. When we initiate BF its a race against the timers. Anyone of the timers going is all you need to initiate a BF trip. We deploy this logic on pretty much all breakers at all voltage levels.

Weather or not your have breakers on the high or low side of the transformer determines how much of the power system needs to be cleared for a transformer fault; it has nothing to do with how you deploy a breaker fail protection. If you don't put in a high side breaker than you better have comm's with the remote terminal, because now you need to clear the entire line for a transformer fault. If you don't have the high side breaker you need to send a 77 to the other terminal breakers, which would also cause a BF initiate on those breakers.

 

[bacon4life]

Every fault location should have be able to be cleared by both primary circuit breaker(s) and by backup protection activating other circuit breakers. Using BF logic is one form of protection, but other kinds of backup protective elements may also be used. BF is typically faster than backup distance/backup overcurrent elements, but BF tripping also adds more complexity to the installation.

marks1080-Are recommending to initiate breaker failure tripping for manual/SCADA trips as well as protection trips?

 

[Mbrooke]

@Marks1080: I disagree, but its most likely my own wording that is causing the confusion. BF is a protection thats initiated by other protections that call for the breaker to trip.

When protecting a transformer its not a good idea to use AND logic because a transformer may not generate enough current during a fault to pickup fault detectors. Instead have it such that over current detectors OR 52A have the ability to qualify as breaker fail indicators. Meaning either alone can can count as BF indicators.

Here is what I have in mind. It does not mention transformers, but shows the logic I am talking about:

https://www.nerc.com/comm/PC/System...PCS_Breaker_Failure_Design_approved_by_PC.pdf

 

[davidbeach]

We use just current based BF everywhere except generators where the 52a enters the picture as well; but I can see why transformers may benefit from breaker position based breaker failure protection as well. With a few generators and lots of transformers and the times that the 52a has caused a BF misop I'd be leery of going there with transformers. (Though with more 52a sensitive locations that trap might become less sensitive.)

While some might do otherwise, I'd never initiate breaker failure on a manual or SCADA breaker open command. For fault clearing the current through that breaker must be interrupted, come hell or high water, but for normal switching the failure of a single breaker to interrupt simply results in a need to go to plan B. Load currents, charging currents, loop currents, and etc. can all be interrupted with devices that one would never consider for interrupting fault currents. A BF trip is almost certainly to result in dropped load, but plan B switching, even if it takes a day or two to implement ought to be possible without any load interruption (assuming the right/wrong fault doesn't occur in the meantime).

Internally initiated BF tripping can have a relatively sensitive fault detector but where we have external BF initiation we set the current detector above load current to avoid the bad things that can happen with spurious BF initiation. The SEL-4xx relay with multiple types of BF protection is handy in that respect.

Lines and transformers all do their own BF protection; bus relays may simply trip the bus lockout and each position on the bus then sees that lockout as a BF initiation signal. That way low-Z bus diff and high-Z bus diff both get treated the same even though one could do it's own BF and the other can't. Also less wiring for the bus relays.

 

[Mbrooke]

Great info- though to me knowledge you can't interrupt load current with an isolator unless it has an SF6 attachment.

 

[crshears]

@ my utility it is policy to not initiate BF from manual or SCADA trips. I've also heard it stated that "the operation of breaker fail will not initiate breaker fail," meaning that there will be no cascading equipment operations due to the operation of a breaker failure detection scheme.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[davidbeach]

We cascade breaker failure. I don’t have any first hand examples, but I’m aware of situations others have had where multiple breakers fall simultaneously. One example was a station where the wrong grease had been used during breaker maintenance and multiple breakers failed to operate at low ambient temperature conditions.

 

[marks1080]

bacon - No sorry, i wasn't thinking about SCADA trips. great point! We don't currently initiate breaker fail on SCADA trips - but there's an argument to be made to do so. The main point against is that it wasn't a protection system initiating the trip, therefore there should still be a protection system (at least one) standing by to clear the fault (failed breaker). However it is easy to imagine a mechanical catastrophic failure where you would have been better off hitting the BF initiate with the SCADA trip.

mbrooke - we are much more conservative with our transformers. The current pickup level used for breaker fail is quite low. I think we just do it differently.

62a is becoming obsolete with the speed of the new breakers. You can make a case for disabling 62a (based on adv. 52/a). A lot of new breakers don't even have an 'advanced' pallet because they are so fast.

crshears - the old school concept of 'breaker fail shall not initiate breaker fail' is dead and over. We do it all the time now. The limitation to this was in the old DC logic for the electomechanical systems. We also are ok sending trips to failed breakers now, which is something we never did in the past. The IEDs are capable of controlling the trip seal in so that if a trip did go into an already failed breaker it's limited to 400ms.

 

[Mbrooke]

Advanced pallet? Sorry I'm tired today lol.

 

[marks1080]

It was expected to see older breakers come with adv. pallet. Sometimes it's its own mechanism separate from the main pallet stack, sometime you see it as one of the pallets off the main stack thats been tuned a bit differently. The difference between adv. A pallet and A pallet is that the Adv. A contact should close immediately when the mechanical mechanism starts to move, where as the normal A pallets typically close at some point during the middle of the travel. New ABB SF6 breakers still label an adv. A on the drawings but it's no different than any other A pallet. We manually set these to behave like an adv. A.

So when we set our 62a path timer I use the the time of the adv. a pallet (measured, not guessed) plus two cycles. This typically fall in the range of 50 - 70 ms. That means if there is a BF initiate and the 'adv. A' pallet doesn't open in the logic within that time you trip the zone.

Further to the convo: we use 62b path (electrical failure) at about 150ms, typically supervised by a 52a and an O/C device. So if your pallet shows open, but you still see current -> trip the zone.

Our final path is 62c and is set as a backup with 400ms. If the zone trips on this pathway it means you got problems lol.

 

[Mbrooke]

Why 62C? I'll admit I haven't seen it done the way you describe, but then again we might be talking about the same thing just using all the different terms and expressions lol.

 

[marks1080]

Mbrooke - I must have been sleepy too. I just re-read what I posted and there are a few mistakes there. But in general I think we're talking about the same thing. The 'advanced' pallet was something I saw all the time when I got into the business 10 years ago working mostly at older sites. I don't see 'advanced' pallets come with new fast SF6 breakers, but we still designate one as 'advanced' and try our best to set it accordingly. '62' is just to denote a timer. Our breaker fail has 3 paths (another lie but I'll explain later). Our 62a path is meant to pick up mechanical failure of the breaker, which is why the 'advanced' pallet is used. So if the mechanical operation of your breaker is slowing down or if the linkage falls to pieces, in theory the 62a will time out before the expected change in mechanical position and trip the zone. I like to set my 62a by adding two cycles to the actual measured contact opening time done during commissioning, with 75ms being the max. 62b picks up electrical failures. So the breaker 'opened' but there's still current. For this we use a 52/a pallet and an overcurrent element. If the breaker looks open but there's still current -> trip the zone. This timer I've seen set between 90 - 180ms. 62c path is what I really screwed up above. It's not just a time backup, nor is it for 400ms 62c is a last ditch effort in case the 62a and b timers don't go but another protection is continuing to call for a trip. We consider this to be an uncleared low magnitude fault scenario. It's supervised only by 52/a and a timer. For LV breakers we use 300ms and 500ms on high voltage breakers, to coordinate with adjacent zone 2 timed back up protections (400ms).

The fourth path I eluded to above is the early trip path. It's my favorite path. It's a protection against the workers So when a worker is doing breaker fail maintenance and accidentally picks up a breaker fail trip bus (very very bad thing to happen during routine maintenance, but also very very easy to do) the early trip path will just trip the breaker you're working on, which, unless the breaker actually decides to fail at that moment, should defeat all the 62 path timers and cancel the breaker fail zone trip. Breaker fail protections generally don't trip the breaker they are a part of, rather the breakers of the surrounding zone. A miss-operation causing breaker fail to fire is a bad place to be.

Newer IED's will often have their own internal 'breaker fail' logic. This is going to be different depending on the manufacturer. We're ok using some of them, but others we might not. It's always an option to deploy the philosophies described above in the logic. Some of the manufacturers have their own internal breaker fail elements that are basically what I described above.