9A current inside conductor

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winnie said:
That bare conductor is the secondary of an unintentional transformer, a shorted secondary.
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Hi Jon
what you said about shorted secondary makes lots of sense to me. would you please explain how to remove the shorted secondary?

Have you confirmed that the supply is actually grounded?

-Jon
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Jon, would you please explain to me how you would go about confirming the ground? as I am in the state of confusion.

Drive has its own ground bus, there is no one common ground bus inside the electrical panel.
 
Before we continue this discussion any further, my guess based upon your questions is that you are not strong on the theory behind the electrical work. I have to caution you that I am on the opposite side of the fence. I am _not_ an electrician. As stated in my profile, I do research on electric motors. I am _very_ strong on the theory behind things, but do not want you to believe that I am an electrician.

powerelectronic said:
Hi Jon
what you said about shorted secondary makes lots of sense to me. would you please explain how to remove the shorted secondary?
I believe that this condition needs to remain. It is a natural fact of life if you have equipment attached to building steel, and also have an equipment grounding conductor. Since the steel is likely to remain and the EGC is required, you are stuck with multiple paths in your 'bonded metal'.

You could _minimize_ this current flow if you replace your separate conduit feeder system with one large conduit or two conduits each with a three phase set of conductors. By placing your conductors closer to each other you minimize the magnetic field that they project into the surrounding space.

However I don't see this parasitic transformer with shorted secondary as a significant problem. It will increase voltage drop in the feeder slightly, and it may slightly reduce fault current in the event of a short circuit, but beyond this I don't see any sort of safety issue.

powerelectronic said:
Jon, would you please explain to me how you would go about confirming the ground? as I am in the state of confusion.

Drive has its own ground bus, there is no one common ground bus inside the electrical panel.
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I was asking about the supply transformer. Have you confirmed that the supply transformer is actually electrically connected to the building grounding electrode system?

If the drive has its own ground bus, what is it bonded to? Is there electrical continuity between the drive ground and the panel?

-Jon
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May I join?

I hope that all your load on the 480V are balanced 3-phase loads so that all current in the 3-phases cancels each other out and no circulating current runs in your system. As far as I know, a bare conductor running along with the phase wires is an equipment grounding. Thus, it bonds the non-carrying metal parts of your equipment. If in case any of your load has a single phase load connected line to line or line to ground that might be the cause for your 9amps. If it line to ground, then your equipment ground is also acting a neutral. This is bad because it energizes the non-current carrying metal parts that is touched by it. If this is the case, the solution to this is provide a insulated neutral wire for the 1-phase load. Most motor controls require 1-phase so it requires a neutral. So it might be inside one of your controller. Having no neutral, someone might have connected a single phase load line-to-ground (either directly on the bare copper or to any of the metal parts that your grounded wire is boned) thus giving him a 277V single phase. 277V are common requirements for motor controllers used by 480V motors.
Another is you can check if all current on each phase is equal, if not, maybe that is where your 9amps is coming from. your 9 amps is coming from your unbalanced load.
It could also be that one of your equipment is grounded, if possible try disconnecting each load and see if your 9amps disappear with any of the load you disconnect. If a load happens to be the source of the 9amps then have it checked. If its a motor, there might be a problem in the winding, maybe one of the phase is grounded. Or maybe it has the condition I stated earlier.
 
winnie said:
When I look at the picture of the feeder conductors to the panel, the source of the 9A in the bonding conductor jumps out at me.

You have a bare conductor that goes back to the supply transformer, presumably bonded to the enclosure of the transformer and the panel. There are almost certainly _other_ electrically continuous paths between these two enclosures; possibly conduit runs, building steel, really good grounding electrodes, etc. So the bare conductor is almost certainly part of a closed loop.

The supply conductors are in separate conduit runs, so they will have 'loop area' between them, and will produce a considerable magnetic field in the space surrounding them.

That bare conductor is the secondary of an unintentional transformer, a shorted secondary.

As far as diagnosing your drive failures, I do not have enough experience to hazard a guess. The only times that I've had to deal with drive failures have been when our in house power electronics has not been up to snuff and we blew output IGBT devices. Have you confirmed that the supply is actually grounded?

-Jon
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I don't see separate conduit runs. All I see is six conductors in cable tray.
 
I'll grant that they could be non-metallic insulated conductors rather than conductors in conduit.

The way all of the conductors have the exact same shape of bend and the color said 'conduit on a trapeze' rather than 'cables on a tray'.

But this makes no difference with respect to the magnetic coupling between the conductors and the bonding conductor, which is the core point that I was trying to make.

If these are conductors in a cable tray, then the coupling to the bonding conductor might be reduced or eliminated by introducing 'transitions' in the conductor arrangement; but I would not want to deal with the analysis of all the implications of such a modification.

-Jon
 
is that bad enough to shut down the operation?

is that bad enough to shut down the operation?

winnie said:
But this makes no difference with respect to the magnetic coupling between the conductors and the bonding conductor, which is the core point that I was trying to make.

-Jon
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is the issue of 9 A current in the electrical panl critically bad enough (against NEC code?) to call for an immediate remedy? is that something we should or shall to do someting about it.

Jon, how does the leakage current have to do with the drive inoperatable, since we have to replace vfd drive on regular 4 monthes basis,

What the the magnetic couple, secondary short, and 9 amp overall in the electrical panel have to possibly do the the drive failure? I am very puzzled.


Please refer to the earlier post for background info.
dave said:
With the 9A in ground mystery remains unsolved, we have another AC drive failed. it is GE AC drive AV300i, mounted on the chassis inside the electrical panel (where 9A is detected from ground cable)

GE AC drives have the power amplifier board mounted on the top of heat sink, that is mounted on the top of chassis.

GE drive is not cheap, and this is the second time the same typies of drive failed. To clarify, here is sequence of event:
-E-stop is trigged
-motor brake (external mechanical brake) is engaged
-motors come to stop
-reset E-stop
-run the cycle from the beginning of step one (no ride through)
-certain drive is inoperable

there is no fault code can be retrived, since the operator panel is blank
,unknown cause indeed, or i am missing some crucial clues that aid diagnosis.

this is the second time the same type of drive failed, inside the same electrical panel(fed with 3 phase, star secondary, ), my feeling is that without identifying the cause of failure, we are set to deal with another drive failure down the road,
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dave
 
Dave,

I will repeat my message above. It appears that I messed up the quoting, so it is kind of hard to follow.


Before we continue this discussion any further, my guess based upon your questions is that you are not strong on the theory behind the electrical work. I have to caution you that I am on the opposite side of the fence. I am _not_ an electrician. As stated in my profile, I do research on electric motors. I am _very_ strong on the theory behind things, but do not want you to believe that I am an electrician.

powerelectronic said:
Hi Jon
what you said about shorted secondary makes lots of sense to me. would you please explain how to remove the shorted secondary?
Click to expand...

I believe that this condition needs to remain. It is a natural fact of life if you have equipment attached to building steel, and also have an equipment grounding conductor. Since the steel is likely to remain and the EGC is required, you are stuck with multiple paths in your 'bonded metal'. Multiple parallel paths through the equipment ground system and bonded metal are expected and often required.

You could _minimize_ this current flow in this 'parasitic transformer' if you re-arrange things to minimize the magnetic field produced by the feeder conductors. This could mean moving conductors into conduit which contain complete three phase sets, or possibly simply re-arranging the conductors in the cable tray. By placing your conductors closer to each other you minimize the magnetic field that they project into the surrounding space, and reduce the current induced in other conductors nearby. But you will not be able to eliminate these induced currents.

At the same time, I don't see this parasitic transformer with shorted secondary as a significant problem. It will increase voltage drop in the feeder slightly, and it may slightly reduce fault current in the event of a short circuit, but beyond this I don't see any sort of safety issue. 9A is being induced into the bonding conductor, but I don't see this as causing significant voltages.

powerelectronic said:
Jon, would you please explain to me how you would go about confirming the ground? as I am in the state of confusion.

Drive has its own ground bus, there is no one common ground bus inside the electrical panel.
Click to expand...

I was asking about the supply transformer. Have you confirmed that the supply transformer is actually electrically connected to the building grounding electrode system? Is there a bond between the transformer secondary winding and the grounding/bonding conductor system?

If the drive has its own ground bus, what is it bonded to? Is it electrically connected to anything? Is there electrical continuity between the drive ground and the panel?

-Jon
 
how much is the minimized current?

how much is the minimized current?

Jon,
when the transformer is off, there is ma current in the grounding conductor(or in your word, the shorten secondary, or just bare conductor shown in picture),

when transformer is on, but all vfd inverters are off, there is 8A current in the bare cable.

is that logically to say the current is from the transformer line said, not from load side of drives??? i believe that transformer is the only power supply to the electrical panel.

there are three racks of drives, each rack has its own ground bus that attached to chassis, and electrical panel sits on the steel frame.

again, giving drive failure history, is that necessary to minimize the 9A current in bare conductor, are there any rules that set limits to the objection current in the electrical panel?????

and on the same line of question, how much A is "minimized" A?
 
As george points out, but how the rules applied in this case

As george points out, but how the rules applied in this case

georgestolz said:
powerelectronic said:
Eric
If the transformer is bonded
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would you please explain what "bonded" means?
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For a definition of bonding for ungrounded systems, see 250.4(B)(2), (3) and (4).

For a definition of bonding for grounded systems, see 250.4(A)(3), (4) and (5).
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please elaborate, everyone?
 
PT said:
May I join?

I hope that all your load on the 480V are balanced 3-phase loads so that all current in the 3-phases cancels each other out and no circulating current runs in your system. It could also be that one of your equipment is grounded, if possible try disconnecting each load and see if your 9amps disappear with any of the load you disconnect. If a load happens to be the source of the 9amps then have it checked. If its a motor, there might be a problem in the winding, maybe one of the phase is grounded. Or maybe it has the condition I stated earlier.
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Hi PT,
Hi all,
here is the latest readout of current
at the electrical panel
L1 105.1,105.1
L2 103.3,111.6
L3 109.1, 79.5

current at the service entry of plant
L1, 143,170
L2, 139,203
L3 164,179.8
neutral, 3.8,5.6

how bad it is???

also
 
Karl is right, your wire acts as a parallel neutral. If your load is balanced in a 3-phase system and you have a clamp ammeter wherein you can place all your phase wires (L1, L2 & L3) together, the reading should be zero; everything cancels out. Having an unbalanced load, there must be another conductor where the uncancelled current must run, this is one of the reason for a neutral conductor. The neutral is an insulated for reason it carries current.
As in the picture, your conductor is bare, I think it also bonded to some metal parts of your system. Your bare conductor is energized then some of the metal parts of your system is energized. you might or might not able to notice it. What I mean is any personnel experiencing having a tingle of electric current run thru when accidentally in contact with metal part of your system. If you haven't yet, it's because your bare copper is doing a good job as a neutral, as job that it should not be doing. If possible, have the motor (experiencing this 9A) tested for any ground. Megger test it if possible. Then if you have cleared it of any ground, provide a real neutral wire from the X0 of your transformer to your whole system.
I hope that will fix your problem.
 
Hi PT,
Thank you for the big picture, I want to follow up with you on the some small details, by asking you the same question that I asked jon earilier....
when the transformer is off, there is ma current in the grounding conductor(or in your word, the shorten secondary, or just bare conductor shown in picture),

when transformer is on, but all vfd inverters are off, there is 8A current in the bare cable.

is that logically to say the current is from the transformer line said, not from load side of drives??? i believe that transformer is the only power supply to the electrical panel.
Click to expand...

if you agree that there is current from transformer, then should the megger testing on motor can be omitted? or not, in the nutshell, would you please explain why it is good time to do megger test, what do you expect to verify?

thanks again
 
What do you by "the transformer is off"? Do you mean totally disconnected at the line side? If this is so, do you have any other power source in your building. Because as I have said earlier, the bare conductor is bonded. Any current, it may be a residual current or a current that is coming from another source which is looking for a path to ground may use the said bare conductor.
Or you just shut -off all of the load connected? So it is still connected, the controls are still on-line.
Or you disconnect all the load? Then we go back again to your other source! Is your 2nd electrical source properly grounded? Maybe that system is experiencing a slight line to ground fault. Slight, meaning it's not big enough to trip your breaker. And that leakage current that your second system is experiencing has no good path to ground and thus utilizes the conductor that we were discussing as its path to ground because your whole building is bonded. Bonding is a good thing and is a must for safety reasons. It has a draw back because for slight line to ground fault, it makes locating it difficult because all systems are connected.
 
the transformer maybe the only source of that panel, but as i have said, there are other sources in your building that your building is bonded by its grounding. and I'm sure that even if you disconnect the line of your transformer, and if it was your other source that is supplying the current, then your bare conductor which is still directly connected to ground in the secondary by it X0 terminal (even if you disconnect the primary) is the path to ground of that current coming from the other source.
I had an experience on that, current coming from another source that was not properly grounded passing thru the good grounded EGC of another. Luckily we were able to trace where the slight line-to-ground fault. It was a shocking experience to all who touched any of the metal on that building.
I hope you find yours.
 
PT said:
if you disconnect the line of your transformer,...I hope you find yours.
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Hi PT
Please look into this diagram,
transopen.jpg


after disconnect the lines of transformer, the current read out in bare cable is 8mA. is that permissible?

if yes, then can i conclude that most of current in bare cable comes from the transformer (induced? maybe)?? and the solution is to pull neutral wire??

Bounding....is that necessary at this point to check on the load sides since all bounded to the steel structure? is that possible that drives are failed by the ground fault current while the lines are shuttng down? how to prove it?

There is dip just before the line shut down, we have power factor capacitor bank switch on and off, and drive is failed due to overvoltage, plus 9A current in grounding conductor,

Please let me know your thought.
 
As per your diagram, the center of your wye is connected to ground, it is not also connected to to the load? You have a capacitor bank, that can also be factor in your mystery current.
Some drives are very sensitive, sometimes we install AVR or TVSS to protect them from over-voltage.
 
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