3000A Ground Fault Protection breaker tripping
3000A Ground Fault Protection breaker tripping
(OP)
I had a 3000 amp 480 volt breaker trip on a Ground Fault. The Hmi for the ground fault showed 79Amps. I did find a 36kw heater with all 3phases grounded. It was fed with (3) 50a LPJ fuses. 1 of the fuses was blown.
In the future I would like fuses to open before tripping the 3000 amp breaker. Does anyone have any suggestions as to what sort of protection should be implemented to act faster than a ground fault protection ?
In the future I would like fuses to open before tripping the 3000 amp breaker. Does anyone have any suggestions as to what sort of protection should be implemented to act faster than a ground fault protection ?






RE: 3000A Ground Fault Protection breaker tripping
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RE: 3000A Ground Fault Protection breaker tripping
I understand that the ground fault breaker did what it was supposed to. But let me assume that in the future something bad happens to another heater( I have many heaters on site all with similar fusing) what I would like to avoid happening is 3000 amp main tripping on a ground fault that feeds dozens of other loads.
The 3 phase 480 volt supply(hot) conductors feeding the heaters are not normally grounded. But today something bad happened.
Thanks,
RE: 3000A Ground Fault Protection breaker tripping
The ground fault trip unit will have time delay setting adjustments. For a breaker this large, you will want a fairly long time delay to allow downstream protection time to clear the fault.
What type of trip unit and what pickup and time delay settings?
RE: 3000A Ground Fault Protection breaker tripping
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RE: 3000A Ground Fault Protection breaker tripping
Consider more GFI breakers. Your distribution panels may be retrofitted with ground fault breakers set lower than the main breaker.
As an alternative or addition, the breakers feeding the heaters may be retrofitted with GFI breakers. With proper coordination, the breaker closest to the ground fault will trip first and isolate the fault without interrupting service to other devices.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 3000A Ground Fault Protection breaker tripping
Rafiq Bulsara
http://www.srengineersct.com
RE: 3000A Ground Fault Protection breaker tripping
When a high harmonic load with lots of neutral currrent comes on, the swapped CT will cause a GF trip.
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
The GF delay was set to 0s and the pickup was at 120A.
I changed the GF delay to .2 sec.
The GC DSP showed the I(g)"last trip" as 79A. After talking to tech support they suggested with no delay, relay actuates faster then display.
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
Alan
----
"It's always fun to do the impossible." - Walt Disney
RE: 3000A Ground Fault Protection breaker tripping
Nonsense, the relay has to see Igf above pickup and will record it, something is amiss here, when is the last time this GF system was tested?
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
In an integral ground trip unit, the lowest available setting would probably be 0.2 or 600 A. We would likely set it much higher than that, with a long time delay.
RE: 3000A Ground Fault Protection breaker tripping
Sadly, the basis for original settings such as this one are rarely documented (other than by the firm that did the design). One often has to reverse engineer things to deduce what they were thinking.
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
If it has been tested the documentation went the way of the dinosaur.
As for the coordination study , they might have taken the dimensions of the gear and figured out they could put it in said location.
Tech support said in the absence of design specs the factory default position for time delay is 0 and pickup 120A.
I believe it has been operating this way for about 8 years.
The end use load with the fault in this case was a 36kw heater fused at 50amps with a 200amp I line breaker feeding the fuses all originating from the 3000amp breaker with the ground fault relay.
Tech support is stating that if ground fault relay set above 200amp pickup all sorts of bad things could/will happen and that I need to implement even more ground fault protection to be safe.
Is this a case of bells and whistles being added on to bells and whistles?
Or does this sound normal to someone.
I have not seen in the field supplementary ground fault protection for motors and heaters.I have seen it for heat tape.
And in my bathroom about once a year the GFI trips .
RE: 3000A Ground Fault Protection breaker tripping
nonsense. I would commonly set it up around 0.5 sec and 1000A. Again, coordination study is needed.
A second level of ground fault protection can frequently improve coordination. You can certainly install branch circuit breakers with ground fault trip, for $$. This is not the solution to your present problem.
My favorite quote:
Alan
----
"It's always fun to do the impossible." - Walt Disney
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
They might be correct. There may be something downstream that needs that level of sensitivity for GF protection. Perhaps a GF function needs to be added to a branch circuit (or several) downstream.
Dialing in a time delay might fix your problem. But, aside from that 36 KW load, what else lies downstream of the 3000A breaker and what sort of TD value will achieve coordination with the rest of your system?
RE: 3000A Ground Fault Protection breaker tripping
You may increase the trip setting on the breaker so that ground faults are cleared by the fuses, but, you may end up boiling a lot of water in a similar instance if a ground fault is not drawing enough current to blow the fuses. It takes awhile for 79 amps to blow 50 amp fuses. It is possible that the next time that a junction box is flooded the fault current may not be enough to blow the fuses. I don't see a higher setting on the only ground fault protection as a good idea.
The reason that the codes call for ground fault protection on large installations is to prevent large scale damage in the event that a serious arc to ground is not cleared by the over current protection.
OR
You may install ground fault breakers coordinated with the main breaker so as to clear ground faults without taking the whole plant down. The added breakers may be the main feeds for panels or installed on the individual circuits, or both.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: 3000A Ground Fault Protection breaker tripping
Most of the end use is motors,roughly (40) 20 hp + 40 1/2-10hp motors.
125kw of heaters .
The biggest I line breaker in the switchboard is 800 and the smallest is a 60.
What concerns me about adding more GF protection is the possibility of more nuisance tripping. Granted it would save the 3000 amp main. But if say instead of a 15amp fuse blowing now I am taking out 200 amp GF breakers. I will not be getting a raise.
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
Your concerns are valid and your thinking as well. Plus adding GF at lower levels is expensive and is not normally done in systems like yours. The key is to set your GF pickup (and delay) on the main less sensitive than all or most of your feeder/branch breakers.
The NEC permitted maximum limit on GF setting, I indicated earlier, is there for a reason. In fact it is there exactly to address the situation you are in without having to go through expansive studies and engineering. Make "full" use of it.
The alternative is to have a coordination study done by a professional.
Rafiq Bulsara
http://www.srengineersct.com
RE: 3000A Ground Fault Protection breaker tripping
Since powersoff's technicians expressed concerns with changing the original settings, it would be a really good idea not to catch them by surprise the next time they get to wrenching on a live system.
RE: 3000A Ground Fault Protection breaker tripping
No one should be wrenching on a live system to begin with and if they do, surprises should only be expected. Arc flash analysis and PPE although helpful, provide a false sense of security.
Working live should only be a last resort and requires a permint per NFPA 70E. If any settings are messed around for arc flash, they should only be temporary or at least not at the expense of permanent coordination.
PPE only protects against burns not against shrapnel or blast pressure. Even the burn injuries could be a second degree burn while wearing a PPE, which is most painful burn injury but curable. So anyone thinks that just by using PPE as we know today will save them from surprises or all injuries should think twice.
Rafiq Bulsara
http://www.srengineersct.com
RE: 3000A Ground Fault Protection breaker tripping
Rafiq Bulsara
http://www.srengineersct.com
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
RE: 3000A Ground Fault Protection breaker tripping
For systems above 600V, the code requirement is to determine the flash protection boundary at 1.2 cal/cm^2. If I can show where, for a combination of lower fault currents and longer clearing times* the energy exceeds that figure, I'll use my own judgment.
*For 600V or lower systems, although the code specifies the fault power formula, the exposure time is _not_ tied to this current level. If an actual fault is a single phase to ground and the applicable clearing time is longer, then that's the value of 't' you've got to plug into the formula.
RE: 3000A Ground Fault Protection breaker tripping
A 20A fuse or something?
I spose if your main breaker is popping out at 0s then it may not make too much difference but any changes could be minimised in the main breaker if you can size the heater fuse more accurately.
Thanks,
Andrew
RE: 3000A Ground Fault Protection breaker tripping
So there is some range of fault currents for which the suggested fuse will not coordinate with the stated GF setting.