Problem NW 3000A Breaker 6.0P Drawout Indoor Dry Location

[Natfuelbilll]

NW 3000A Breaker 6.0P Drawout Indoor Dry Location

This is a 3000A breaker between a four generator bus system (each with individual 800A generator breakers) and tied to the load side of a utiltiy fed 3000A breaker (grid parallel).

We have had three GF trip events. One a couple of years ago, and the last two within the last two months.

The trip amp details on phases A/B/C of a ground fault trip event were exactly 300/1200/1200, another were 300/1200/1200 and the latest trip event at 600/1200/1200. These values seem to me to be too precise, too repetitive, too fractionally proportional to the breaker trip rating. i.e.: exactly 1/10th, exactly 1/5th and exactly 2/5ths. It seems unlikely to me that an actual ground fault would provide these repeatable fractional values. The breaker ground fault trip setting is now 500A.



Also, the trip events had no trip date.
300/1200/1200 no trip date
300/1200/1200 no trip date
600/1200/1200 no trip date
The Time/Date screen has correct data

Talked to SquareD - they can't explain the readings.
SquareD Quote #1 is to go over the breaker and wiring $$
SquareD quote #2 is to study the power system for multiple NG connections and adjust GF amp values. $$$

Do you think the recorded amp values are correct?

Did I have a GF?


Here, I'll give some of my hair that I have pulled out.

 

[Phil Corso]

Natfuelbilll...

Presumably this is an LV system! And all gen neutrals are grounded together with utility xfmr's neutral.

Have you measured current(s) in each of the five (5) Neutral-GroundING conductor's?

Regards, Phil Corso

 

[templdl]

It's been a while since I have been involved with metal clad or power breakers but it appears that you are looking of and exact value of the fault when you are getting at what point the breaker tripped. If you had a current rise to the point at which you set the breaker it would trip at that point and not what the current would be if it was to go unchecked to a maximum current.
Does this make sense?
It is of my opinion that because the setting is an instantaneous setting you have set the trigger point setting and it is that point that the breaker is indicating.

 

[jim dungar]

Do you have a modified differential ground fault scheme (MDGF)?

Has the complete ground fault system been field tested, or do you just test the breaker trip unit?

 

[Natfuelbilll]

Natfuelbilll...

Presumably this is an LV system! And all gen neutrals are grounded together with utility xfmr's neutral.

Have you measured current(s) in each of the five (5) Neutral-GroundING conductor's?

Regards, Phil Corso

Yes, this is a 480v system.
Generator neutrals not bonded at each generator but are tied together in the generator paralleling switchboard unbonded till they reach the single point NG bonding location in the utility fed switchboard. Otherwise there would be shared normal neutral currents on the egc and conduit.

 

[Natfuelbilll]

It's been a while since I have been involved with metal clad or power breakers but it appears that you are looking of and exact value of the fault when you are getting at what point the breaker tripped. If you had a current rise to the point at which you set the breaker it would trip at that point and not what the current would be if it was to go unchecked to a maximum current.
Does this make sense?
It is of my opinion that because the setting is an instantaneous setting you have set the trigger point setting and it is that point that the breaker is indicating.

I think you are saying that the recorded values don't make sense to you either?

 

[Natfuelbilll]

Do you have a modified differential ground fault scheme (MDGF)?

Has the complete ground fault system been field tested, or do you just test the breaker trip unit?

I think I have a MDGF scheme, but the ^;$#> vendor won't provide the gear drawings - grrrrr

Neither the ground fault system nor the breaker GF has been recently field tested. Is this a best practice? What is the typical cost of that testing? $3k? $30k?

Thanks everyone!

 

[Phil Corso]

NatfuelBill...

The reason for measuring the neutral current ss to determine ifharmonics are present! And if they are are they present with or without the Utility connnection!

Phil

 

[Natfuelbilll]

Natfuelbilll...

Presumably this is an LV system! And all gen neutrals are grounded together with utility xfmr's neutral.

Have you measured current(s) in each of the five (5) Neutral-GroundING conductor's?

Regards, Phil Corso

No, I have not measured these neutral currents with any handheld instruments.

I do see Ig (ground) currents on the generator and generator main breaker of 10A gen#1 0A gen#2 0A gen#3 gen#4 is off and 22A on main

And I see In (neutral) currents are 11A gen#1 (micrologic 6.0 P) no reading on gens #2 #3 (micrologic 6.0A) and 0A on the main.

 

[zog]

I agree the trip readings are just to percise to be the result from an actual fault. The bets thing to do like has been mentioned is to have the breaker and ground system tested, not as expensive as you think, I would however get a 3rd party to do the testing so you are sure you get a honest opinion. If you PM me where you are located I can recommend a few good testing companies near you.

There is a recall notice on micrologic trip units, in your case with a 6.0A model the affected date codes are April 2001-Dec 2005, so I would check that first, the reason fro this was nuisance tripping from transient noise, which sounds likely in your case.

Are you using a nuetral CT or a 3 wire system? That is key info here as well.

As far as your lack of of trip log info my first thought would be a dead battery, these trip units have a history of battery issues (I.N. also released by SQ-D) due to passivation, there is a depassivation procedure, or you can replace the battery. If your battery is dead, which will happen fast if you don't have enough load on the breaker for the CT's to power the trip unit, you will not have a fault history log.

 

[Phil Corso]

Natfuelbilll...

1) Do you have, or can you obtain utility xfmr no-load ph-ph and ph-neutral and ph-grd voltages?

2) Are gen's dissimilar in design ratings, or mfgr?

3) Do Ig currents change wit load?

4) How about some capacity info covering the five electrical apparatus (or aparatuses or is it apparati)?

Phil

 

[Natfuelbilll]

As far as your lack of of trip log info my first thought would be a dead battery, these trip units have a history of battery issues (I.N. also released by SQ-D) due to passivation, there is a depassivation procedure, or you can replace the battery. If your battery is dead, which will happen fast if you don't have enough load on the breaker for the CT's to power the trip unit, you will not have a fault history log.

The trip unit is powered by a station battery. Also, SquareD tech service doesn't understand why there is no date but I do have trip values recorded...

 

[Natfuelbilll]

Natfuelbilll...

1) Do you have, or can you obtain utility xfmr no-load ph-ph and ph-neutral and ph-grd voltages?

2) Are gen's dissimilar in design ratings, or mfgr?

3) Do Ig currents change wit load?

4) How about some capacity info covering the five electrical apparatus (or aparatuses or is it apparati)?

Phil

1) I can get these values later - with some planning.
2) generators are identical
3) Ig currents do fluctuate
4) Gens are 336kW, gen breakers are 600A, main buss is 3000A

 

[zog]

The trip unit is powered by a station battery. Also, SquareD tech service doesn't understand why there is no date but I do have trip values recorded...

I forget these can use an aux 24VDC external signal for that as well.