300kva transformer tripping GFI in 2000 amp switch gear

[Fordean]

In a printing company. They ordered presses @ 480 volts. And they had a service installed years ago at 208. Now we bumped up voltage with Trans. When first energized. Tripped GFI. Now called D tech line. And they stated GFI setting set at factory to zero. I checked and was still at zero. They suggested moving gradually to it holds. Moved it in slight increments. Seemed fine. Now Im told it began to trip. When off hours and closed. Utility. shutting down or Weather related off time. When it comes back online. I Suspect magnetic coils are tripping it again. Can I install a rectifier. If I'm using the correct terminology. Any suggestions. What is a normal GFI dial setting. I have to do the math I'm sure. But wunder why it was on zero to begin with.

 

[kwired]

In a printing company. They ordered presses @ 480 volts. And they had a service installed years ago at 208. Now we bumped up voltage with Trans. When first energized. Tripped GFI. Now called D tech line. And they stated GFI setting set at factory to zero. I checked and was still at zero. They suggested moving gradually to it holds. Moved it in slight increments. Seemed fine. Now Im told it began to trip. When off hours and closed. Utility. shutting down or Weather related off time. When it comes back online. I Suspect magnetic coils are tripping it again. Can I install a rectifier. If I'm using the correct terminology. Any suggestions. What is a normal GFI dial setting. I have to do the math I'm sure. But wunder why it was on zero to begin with.

First you need to know if it is tripping because of ground fault or if it is the magnetic trip function. I would guess the magnetic trip because of high inrush current is more likely. Is there an adjustment for that?

I doubt a rectifier is what you are looking for - that would convert AC to DC. Maybe a line reactor is what you were trying to think of? It could help if it is a magnetic trip problem because of high inrush current.

 

[Joe S.]

Is the problem only when trying to energize the transformer? If so, we had that problem with new 300KVA transformers a few years ago. The manufacturer wouldn't openly admit it, but the xfmrs made at that time had an inrush of 20 times rated current. We couldn't get the 480V breaker feeding the transformer to hold, and the breaker upstream of that one tripped too. We were only 20 ft from the unit substation. Probably need to change transformers or increase the cable length between transformer and breaker. Maxing out the breaker trip rating didn't help us.

 

[templdl]

In a printing company. They ordered presses @ 480 volts. And they had a service installed years ago at 208. Now we bumped up voltage with Trans. When first energized. Tripped GFI. Now called D tech line. And they stated GFI setting set at factory to zero. I checked and was still at zero. They suggested moving gradually to it holds. Moved it in slight increments. Seemed fine. Now Im told it began to trip. When off hours and closed. Utility. shutting down or Weather related off time. When it comes back online. I Suspect magnetic coils are tripping it again. Can I install a rectifier. If I'm using the correct terminology. Any suggestions. What is a normal GFI dial setting. I have to do the math I'm sure. But wunder why it was on zero to begin with.

You didn't specify where the GFI was and it would be my guess that there are 2 settings for it, pickup and delay. What is the ampere pickup, and what is the delay set at.
Normally the pickup is a multiple of the breaker rating and the delay is how which of a hiccup you want to give it before it activate.
I would be nice if you were to provide the description of the GFI as it would prevent a lot of guessing on our part.
Remember, in most cases the settings on a GFI such as the one that you are referring to are there for coordination with other GFI devices. Otherwise, unless a manufacturer of the equipment being supplied doesn't say otherwise go ahead and set the pickup to the max and the delay at the min. If you want to play with them just so that they are just out being a nuisance you could do that but it's not work the risk.
More often than not there is much to-do about nothing when one sits there ands scratches their head about these settings. As a lone device it?s no big deal in most cases unless an engineer has selected it and then specified what it should be set at. There is no way that you would have a clue yourself.

 

[rcwilson]

Make sure it is the ground fault function that is tripping the breaker. Usually transformer inrush will trip just the instantaneous overcurrent trip. Inrush should never trip the ground fault unless the inrush current is so high that it saturates the GF sensing CT's causing a false trip.

Is the 208V – 480V step up transformer a standard 480V to 208/120V transformer wired backwards? If so, is the 208 volt side neutral connected to ground or the panel neutral? If it is connected to ground circulating currents will false trip the service ground fault protection.

The 208 volt side transformer neutral must not be connected to anything. Just connect the phase leads (X1, X3, X3). Leave X0 floating.

 

[zog]

Or, maybe there is a ground fault?!? Has any testing been done after the modifications? Has the GFP itself been tested?

 

[ron]

Test first and verify what is going on with meters and visual inspection.

It could also be that step down transformers wired as step up's will have higher inrush than normal because of the how the windings are wound in order around the core (which first). You can buy a step up that was designed as step up for regular inrush.

 

[templdl]

Make sure it is the ground fault function that is tripping the breaker. Usually transformer inrush will trip just the instantaneous overcurrent trip. Inrush should never trip the ground fault unless the inrush current is so high that it saturates the GF sensing CT's causing a false trip.

Is the 208V ? 480V step up transformer a standard 480V to 208/120V transformer wired backwards? If so, is the 208 volt side neutral connected to ground or the panel neutral? If it is connected to ground circulating currents will false trip the service ground fault protection.

The 208 volt side transformer neutral must not be connected to anything. Just connect the phase leads (X1, X3, X3). Leave X0 floating.

Good point. Check that X0. You can count on the inrush being 8-10 times the rated current 208v. Isn't the pri FLA@208c 832a? We have no clue what the pri breaker even is.
the inrush should be no more than approx 8000a. Considering that the mag. trip is adjustable aften from 5 to 10X the breaker rating one thing to check is to varify the mag. setting as you had suggested as they do ship in the lowest set point and very often left at that setting.

 

[templdl]

Test first and verify what is going on with meters and visual inspection.

It could also be that step down transformers wired as step up's will have higher inrush than normal because of the how the windings are wound in order around the core (which first). You can buy a step up that was designed as step up for regular inrush.

You are correct regarding the higher inrush.
Because the LV windings are wound first next to the core you can expect that the inrush ratio will be a bit higher energizing the LV winding using the transformer to step up than energizing the HV windings as a conventional set down. I really don't know exactly what to expect the increase on the ratio would be but it will be higher.

 

[brian john]

First transformer and feeder should be tested.
Second the GFPE should be tested.

I would NEVER, NEVER, NEVER close a switch/CB into a possible fault.

Third the most likely reason, assuming you do as noted above, the most likely cause of the tripping is the low settings, the instantaneous inrush for the transformer is resulting in the GFPE CT's/Relay see the imbalance during the instantaneous inrush current.

If you firm is not capable of completing this testing I would hire a firm that can.

Ideally SOMEwHERE there should be an engineer that can give you the correct settings in lieu of guessing and sneaking up on the possible right/wrong setting.

 

[templdl]

First transformer and feeder should be tested.
Second the GFPE should be tested.

I would NEVER, NEVER, NEVER close a switch/CB into a possible fault.

Third the most likely reason, assuming you do as noted above, the most likely cause of the tripping is the low settings, the instantaneous inrush for the transformer is resulting in the GFPE CT's/Relay see the imbalance during the instantaneous inrush current.

If you firm is not capable of completing this testing I would hire a firm that can.

Ideally SOMEwHERE there should be an engineer that can give you the correct settings in lieu of guessing and sneaking up on the possible right/wrong setting.

With a magnetic trip setting there are really no correct of incorrect settings. The only magnetic settings that are adreessed in the NEC is in art 430 regarding a breaker as part of a combination motor starter such as an MCP.
On regular TM breaker for cable protection faults can be arcing and bolted. It is not often an arcing fault will trip the breaker instantaneously because the current most likely is too low. Arcing faults are a bear to detect and a GFI is most likely to pcik it up and a line to ground issue.
The bolted fault is a hell bent for election occurance. Most of the time there is not in between or a sort of a bolted fault and, as such, whether you have the breaker setting lower or higher really doesn't matter. If you set 2 identical breakers side by side one set high and the other set low and both were subjected to and identical bolted fault both would clrear the fault the same.
It is often the same with GF settings but a GF could be arcing where the lowest setting possible with out a nuisance trip would be more desirable. The short time delay if provided doesn't bring much to the party as a lone device. Both the pick up and delay settings would be usefull when coordination with another device.

 

[beanland]

Backward transformer?

Backward transformer?

If you installed a 480V delta to 208Y/120V transformer as a step-up from 120/208 to 480V and if you grounded the star point of the wye winding, the transformer is acting as a grounding transformer and is supplying ground current for faults, includingo nes on the utility system, if that is a wye-wye transformer. A fault on the utility high-voltage system will lead to voltage unbalance and the wye-delta transformer tries to fix the problem by sending ground current. That current will cause the GFI to operate.

Remove the "Xo" connection on the transformer and operate as a 3-winding transformer.

Properly done, you should have used a 208 delta to 480Y/277V wye transformer to avoid the problem.

 

[brian john]

With a magnetic trip setting there are really no correct of incorrect settings. The only magnetic settings that are adreessed in the NEC is in art 430 regarding a breaker as part of a combination motor starter such as an MCP.
On regular TM breaker for cable protection faults can be arcing and bolted. It is not often an arcing fault will trip the breaker instantaneously because the current most likely is too low. Arcing faults are a bear to detect and a GFI is most likely to pcik it up and a line to ground issue.
The bolted fault is a hell bent for election occurance. Most of the time there is not in between or a sort of a bolted fault and, as such, whether you have the breaker setting lower or higher really doesn't matter. If you set 2 identical breakers side by side one set high and the other set low and both were subjected to and identical bolted fault both would clrear the fault the same.
It is often the same with GF settings but a GF could be arcing where the lowest setting possible with out a nuisance trip would be more desirable. The short time delay if provided doesn't bring much to the party as a lone device. Both the pick up and delay settings would be usefull when coordination with another device.

I am not sure of your point in regards to main post and the OP's question. In reviewing his post I see no mention of a circuit breaker. My response has to do with the operation of the GFPE.

 

[Fordean]

BP type switch

BP type switch

I am not sure of your point in regards to main post and the OP's question. In reviewing his post I see no mention of a circuit breaker. My response has to do with the operation of the GFPE.

The switch is a BP type 2000 amp Pressure switch.

The xo connection on transformer. I will look at that. Thanks for response. I will compile a better list of what you all are asking.

Thanks.

 

[rcwilson]

The switch is a BP type 2000 amp Pressure switch.

A bolted pressure switch will only trip on ground fault or fuse blowing, if it has a blown fuse trip feature. So your first assumption is probably correct: the Ground Fault Protection is tripping the BPS.

That leaves four scenarios:
1) an actual ground fault,
2) a false ground fault due to the X0 terminal being grounded,
3) the transformer inrush current creating false GF signals due to sensing CT saturation, or
4) miswiring of the GF system causing a false trip.

I would bet on #2 since the problem was not there prior to the new transformer. But eliminate #1 first. To eliminate #4, check the location of the N-G bonding jumper. It should be on the utility side of the GF sensing CT with no other downstream N-G connections.

Bolted Pressure switches that trip a lot under load can develop rough surfaces on the contacts that keep the BPS from fully closing. It looks closed from the faceplate but it's not. Only a small portion of the mating surface makes contact creating overheating. I have seen two switchboards melt down due to excessive BPS tripping on spurious ground faults. (Both were 480/277V, > 2000A boards. GF's were set low and tripped when 277 V light wiring shorted).

You may want to do some maintenance checks on the BPS.

 

[templdl]

I am not sure of your point in regards to main post and the OP's question. In reviewing his post I see no mention of a circuit breaker. My response has to do with the operation of the GFPE.

Did he indicate what the GFCE is and where if is located? Would it be "assumed" that it is an integral part of the breaker feeding the transformer or a external component? Only after this post PO mention that it was a BP switch. Should the OP have stated what the GFCF was and what it controlled either as part of a breaker of a component that controlled a BP it may have been possible to address his questions more expediently. You response was post #13 I believe and the BP was finally mentioned in post #14.
My response was meant toward a breaker with integral GF. Should a breaker trip is it GF, or inst? How should the setting be set? Also would apply to a separate GF device which it now appears that he has. As such the some answers apply. The settings are there for coordination with other devices otherwise there are no rules as you can set them any where you want unless you are advise by someone qualified that has done a study that would determine a given setting.
When you install one of these devices you see all of the adjustments and think that you must do something with them because they are there. Often times with no direction given you set them just high enough to be out of the nuisance trip range.

 

[brian john]

A bolted pressure switch will only trip on ground fault or fuse blowing, if it has a blown fuse trip feature. So your first assumption is probably correct: the Ground Fault Protection is tripping the BPS.

Bolted pressure switches can have a variety of devices that can trip the switch, phase failure, Blown Fuse, GFP, lately we have seen quite a few phase failure relays defective. The manufactures have stated that the high rate of failure is the devices being meggared.

Bolted Pressure switches that trip a lot under load can develop rough surfaces on the contacts that keep the BPS from fully closing. It looks closed from the faceplate but it's not. Only a small portion of the mating surface makes contact creating overheating. I have seen two switchboards melt down due to excessive BPS tripping on spurious ground faults. (Both were 480/277V, > 2000A boards. GF's were set low and tripped when 277 V light wiring shorted).

You may want to do some maintenance checks on the BPS.

A properly maintained BPS will have arcing contacts that minimize any pitting on the main power contacts, as for BPS burning down during an fault, in all my experiences and I have service 1000's of BPS and been involved in numerous burn downs, is director related to a total lack of service, the use of improper lubricates on the power blades or the spring loaded operators are defective due to the technicians not properly operating the switch, trying to open or close the switch in an non-approved manner.

A switch that will not fully close also has to do with improper maintenance (lubricant) and/or improper adjustment of the closing cams on the side of the power contacts.

 

[brian john]

Did he indicate what the GFCE is and where if is located? Would it be "assumed" that it is an integral part of the breaker feeding the transformer or a external component? Only after this post PO mention that it was a BP switch. Should the OP have stated what the GFCF was and what it controlled either as part of a breaker of a component that controlled a BP it may have been possible to address his questions more expediently. You response was post #13 I believe and the BP was finally mentioned in post #14.
My response was meant toward a breaker with integral GF. Should a breaker trip is it GF, or inst? How should the setting be set? Also would apply to a separate GF device which it now appears that he has. As such the some answers apply. The settings are there for coordination with other devices otherwise there are no rules as you can set them any where you want unless you are advise by someone qualified that has done a study that would determine a given setting.
When you install one of these devices you see all of the adjustments and think that you must do something with them because they are there. Often times with no direction given you set them just high enough to be out of the nuisance trip range.

Actually a few basic common sense rules do apply to just adjusting a GFPE, but I would be leery of just telling someone to adjust the relay current or time. There are liabilities you accept when making recommendations in person or on the phone, that is the event of a system failure resulting in damage or injury would not look goose in court.

At a minimum I would want the GFPE tested to verify proper operation.

 

[templdl]

Actually a few basic common sense rules do apply to just adjusting a GFPE, but I would be leery of just telling someone to adjust the relay current or time. There are liabilities you accept when making recommendations in person or on the phone, that is the event of a system failure resulting in damage or injury would not look goose in court.

At a minimum I would want the GFPE tested to verify proper operation.

I agree. When there are adjustments on a device one assumes that they must be adjusted. But, as I referred to in one of my previous posts the NEC does not address adjustment issues anywhere except the magnetic settings of MCP that I'm aware of. As such one can stand in front of the GFPE and scratch your head and think what do I do now?
Also, the only time that those setting are really important is for coordinating with other devices. The time delay is a benefit, the pickup setting is relative. If it is a lone device what it amounts to is like splitting hairs and there is a risk of it nuisance tripping your BPS. But a qualified engineer should dictate what those setting should be. As far as liability for the setting on a lone device that would be somewhat of a stretch to be liable.
I would be more worried about nuisance tripping and the loss of power that's where back charges and liquidated damages may hurt.

 

[brian john]

I agree. When there are adjustments on a device one assumes that they must be adjusted. But, as I referred to in one of my previous posts the NEC does not address adjustment issues anywhere except the magnetic settings of MCP that I'm aware of. As such one can stand in front of the GFPE and scratch your head and think what do I do now?
Also, the only time that those setting are really important is for coordinating with other devices. The time delay is a benefit, the pickup setting is relative. If it is a lone device what it amounts to is like splitting hairs and there is a risk of it nuisance tripping your BPS. But a qualified engineer should dictate what those setting should be. As far as liability for the setting on a lone device that would be somewhat of a stretch to be liable.
I would be more worried about nuisance tripping and the loss of power that's where back charges and liquidated damages may hurt.

In the court cases I have been involved with lawyers always go for the stretch, and while you may win, you still need to defend yourself which cost. At a minimum I would have the facility sign a document stating they requested the adjustment.

Typically I would recommend the minimum setting of 400 amps, .2 seconds. This gets you outside the majority of CBs in a facility 20 and 30 amp circuit breakers.

In my area I would bet better than 80% of the GFPE systems are left at factory setting s of minimum and an additional 18% are randomly adjusted or turned off to avoid the device from doing it's job. The remaining 2% are set per an engineers study.