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3000A Ground Fault Protection breaker tripping

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 ?

RE: 3000A Ground Fault Protection breaker tripping

In most places using the ground as anything but a protective conductor is a code violation: run a neutral to the star point. It sounds like your breaker reacted in a reasonably foreseeable manner to a badly designed installation.
  

----------------------------------
  
If we learn from our mistakes I'm getting a great education!
 

RE: 3000A Ground Fault Protection breaker tripping

(OP)
Sorry for not being ,clear the connections at the heater were bad/grounded/in water.
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

A 3000 A breaker probably cannot trip on 79 amps of ground current.  I'm not sure what the lowest setting is, but it will be in the hundreds of amps. Maybe 7900 amps? Or a mis-operation.

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

You could install smaller breakers at each load or zone with ground fault trips coordinated to trip before the GF trip in the main.


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RE: 3000A Ground Fault Protection breaker tripping

I assume that the breaker has a shunt trip that is operated by a ground fault detection circuit.
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

For what it is worth, NEC permits up to 1200A GF pick up and 0.5sec of maximum time delay on 480V main. This for the reasons dpc indicated.

Rafiq Bulsara
http://www.srengineersct.com

RE: 3000A Ground Fault Protection breaker tripping

Is your service 3-phase, 4-wire?  If so, possibly the neutral sensing CT is backwards.  Under normal load the meutral current is below the trip point.

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

You cannot generally get fuses to coordinate with a sensitive ground fault device.  As Bill suggested, you need GFI breakers on your branch circuits to the heaters to get coordination.
  

RE: 3000A Ground Fault Protection breaker tripping

(OP)
Today I was able to eyeball the Ground Fault Relay it is a Sq D GC200E.
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

(OP)
My service is 480Y/277 3phase 4 wire.

RE: 3000A Ground Fault Protection breaker tripping

Those settings are still very sensitive for a 3000A service. It probably won't coordinate with downstream fuses unless they are very small (it might coordinate with the 50A heater fuses). You should plot the time-current curves to verify.

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: 3000A Ground Fault Protection breaker tripping

"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. "

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

What kind of system grounding do you have?

RE: 3000A Ground Fault Protection breaker tripping

If this is a solidly-grounded system, that ground pickup setting on a main breaker is much too low.  

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

Quote:

The GF delay was set to 0s and the pickup was at 120A.
I changed the GF delay to .2 sec.
This problem might call for a bit more of a protection coordination study. If that 3000A breaker was originally set as you specified, the intent might have been to protect downstream branch circuits/feeders (arguably a poor design). Now it might be set too high and require some downstream GF protection.

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

I would recommend taking a serious look at every setting on that breaker, if the ground fault is at 120 amps, I would guess that it was never set up in the first place and was just put in a minimum settings.  Find the coordination study and set the breaker accordingly, A 3000 amp breaker ground fault should be set so small breakers (<100amps) will clear faults before tripping on ground fault.

RE: 3000A Ground Fault Protection breaker tripping

(OP)
I love this site.My favorite response so far " something is amiss". I agree.
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

Quote:

factory default position for time delay is 0 and pickup 120A.
I have never seen a breaker that would allow GF time delay set to 0. What kind of breaker is this?

Quote:

Tech support is stating that if ground fault relay set above 200amp pickup all sorts of bad things could/will happen
nonsense. I would commonly set it up around 0.5 sec and 1000A. Again, coordination study is needed.

Quote:

I have not seen in the field supplementary ground fault protection for motors and heaters
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:

Quote:

As for the coordination study , they might have taken the dimensions of the gear and figured out they could put it in said location.

Alan
----
"It's always fun to do the impossible." - Walt Disney

RE: 3000A Ground Fault Protection breaker tripping

When I set up a GF without a coordination study, after looking over the system it generally gets set at 25% of breaker rating and 0.5 seconds, similar to the way Alan commented on setting it up.

RE: 3000A Ground Fault Protection breaker tripping

Quote (powersoff):

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.
And they know this how? That's the sort of thing a protection study will reveal. So if they've already got one, have them cough it up.

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

Quote:

I did find a 36kw heater with all 3phases grounded. It was fed with (3) 50a LPJ fuses. 1 of the fuses was blown.

Quote:

Sorry for not being ,clear the connections at the heater were bad/grounded/in water.
I understand that the ground fault breaker did what it was supposed to.
You had a ground fault and the ground fault protection acted.
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

(OP)
Thanks for all the replies.
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

Could you post the diagram up here. We should see the diagram.

RE: 3000A Ground Fault Protection breaker tripping

powersoft:

Quote:

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.

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

Quote (rbulsara):

The alternative is to have a coordination study done by a professional.
Considering the impact of just tweaking the GF time delay and calling it good will have on things like arc flash protection and maintenance procedures, this would be a really good idea.

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

Let us not confuse a proper GF setting and coordination with arc flash analysis. Basis of device settings should always be coordination.

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

Plus ground fault setting has no effect on arc flash analysis as it only considers 3 phase faults.

Rafiq Bulsara
http://www.srengineersct.com

RE: 3000A Ground Fault Protection breaker tripping

Quote:

Plus ground fault setting has no effect on arc flash analysis as it only considers 3 phase faults.
Protection time delay does affect arc fault energies. And I do consider ground faults when doing these analysis. The worst case cumulative energies can occur for lower power faults (either ground or phase) if the protection for that case is slow.  

RE: 3000A Ground Fault Protection breaker tripping

But none of the calculations of arc energy are for single phase faults.  You don't have any standard or code based reason to look at anything other than three-phase faults when doing an arc-flash analysis.

RE: 3000A Ground Fault Protection breaker tripping

Quote:

But none of the calculations of arc energy are for single phase faults.  You don't have any standard or code based reason to look at anything other than three-phase faults when doing an arc-flash analysis.
That depends on whose standards I'm using. Not everyone buys into NFPA or IEEE formulas blindly.

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

Is it possible to replace the heater fuses with something more sensitive?

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

Quote:

A 20A fuse or something?
A 20A fuse will open with 120A fault current in a couple of seconds. The GF setting of 120A, zero seconds delay is much faster than that.

So there is some range of fault currents for which the suggested fuse will not coordinate with the stated GF setting.  

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