- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Yes, it could be a big problem unless you use an isolation transformer to create an ungrounded delta from the generator's wye output. You cannot run the generator ungrounded.
Ungrounded Delta anomaly
- Thread starter rsnell22
- Start date
- Status
rsnell22
Member
- Location
- Western WA
The voltage to gound was still present when the chiller was isolated. There are other VFDs on boiler draft fans that I cannot just turn off.
Working to shedule a total shutdown and one by one isolating of circuits until the voltage to ground goes away. If the on site staff will allow it.
Right now I have a Fluke 1735 recording, just to CMA.
It gets downloaded tomorrow, and I have a new board for the chiller on the way.
All I have for now.
Working to shedule a total shutdown and one by one isolating of circuits until the voltage to ground goes away. If the on site staff will allow it.
Right now I have a Fluke 1735 recording, just to CMA.
It gets downloaded tomorrow, and I have a new board for the chiller on the way.
All I have for now.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130417-2337 EDT
rsnell22:
If you can be sure that there is no protective circuit of some sort that would object to a 10 A load from one line to ground, then apply such a load and monitor the three voltages to ground. If the source is a rather low impedance, like a wye primary transformer with its mid point connected to ground, then there won't be much change in voltage. A higher impedance source will cause a larger voltage change.
With this kind of single phase load you may be able to go around to various pieces of equipment and look for that current going to ground. If not directly making the measurement, then a flux measuring coil, for example 2000 turns on a 1/2" square core with a 10 microvolt resolution (Fluke 87) meter should allow sensing the field from the ground current near the source of connection to ground. An 0.47 ufd capacitor across the coil will filter a lot of harmonic content.
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rsnell22:
If you can be sure that there is no protective circuit of some sort that would object to a 10 A load from one line to ground, then apply such a load and monitor the three voltages to ground. If the source is a rather low impedance, like a wye primary transformer with its mid point connected to ground, then there won't be much change in voltage. A higher impedance source will cause a larger voltage change.
With this kind of single phase load you may be able to go around to various pieces of equipment and look for that current going to ground. If not directly making the measurement, then a flux measuring coil, for example 2000 turns on a 1/2" square core with a 10 microvolt resolution (Fluke 87) meter should allow sensing the field from the ground current near the source of connection to ground. An 0.47 ufd capacitor across the coil will filter a lot of harmonic content.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
139418-1326 EDT
rsnell22:
My 2000 turn coil of #34 wire shunted with an 0.47 ufd capacitor has an output noise level combined with the meter not over 10 microvolts when I am in a generally free space condition (not close to current carrying conductors).
A relatively separated #12 wire, thus essentially a single wire, with 10 A flow and the center of the coil spaced about 1" from the center of the wire produces about a 7 to 10 millivolts reading.
I have a 1.25" copper water supply line. With the coil adjacent to this pipe the reading is around 1 millivolt. So the water line has about a 1 A reading.
This kind of sensitivity might allow you to find what is creating the apparent ground connection.
.
rsnell22:
My 2000 turn coil of #34 wire shunted with an 0.47 ufd capacitor has an output noise level combined with the meter not over 10 microvolts when I am in a generally free space condition (not close to current carrying conductors).
A relatively separated #12 wire, thus essentially a single wire, with 10 A flow and the center of the coil spaced about 1" from the center of the wire produces about a 7 to 10 millivolts reading.
I have a 1.25" copper water supply line. With the coil adjacent to this pipe the reading is around 1 millivolt. So the water line has about a 1 A reading.
This kind of sensitivity might allow you to find what is creating the apparent ground connection.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130418-2402 EDT
mivey:
The capacitor size was large enough to get rid of high frequency junk, but not too physically large, and it is a size that is in the drawer, and further already had banana plugs that I use with another coil.
The coil inductance is 72 mH, and thus resonant frequency is about 865 Hz.
The coil is a small transformer primary or secondary in a molded package made by the Charles F. Warrick Co, a client of mine in the early 1960s.
One could probably use a Potter & Brumfield relay coil from a KUP relay.
I have a commercial magnetic probe, a wire coil inside an electrostatic shield, that produces about the same results, and is somewhat calibrated. The marked constant is f*20/60 = mV/Gauss. 194 mH and about the same output level 11 mV at 10 A center of coil about 1" from isolated #12 wire.
The reason I used the Warrick coil was because the turns and wire size were marked on the coil. Thus, some reference for somebody.
If needed I can create a picture.
.
mivey:
The capacitor size was large enough to get rid of high frequency junk, but not too physically large, and it is a size that is in the drawer, and further already had banana plugs that I use with another coil.
The coil inductance is 72 mH, and thus resonant frequency is about 865 Hz.
The coil is a small transformer primary or secondary in a molded package made by the Charles F. Warrick Co, a client of mine in the early 1960s.
One could probably use a Potter & Brumfield relay coil from a KUP relay.
I have a commercial magnetic probe, a wire coil inside an electrostatic shield, that produces about the same results, and is somewhat calibrated. The marked constant is f*20/60 = mV/Gauss. 194 mH and about the same output level 11 mV at 10 A center of coil about 1" from isolated #12 wire.
The reason I used the Warrick coil was because the turns and wire size were marked on the coil. Thus, some reference for somebody.
If needed I can create a picture.
.
Last edited:
mivey
Senior Member
gar,
No pic if you don't already have one. Sounds like you made a convenient gauss meter with what you had on hand. I have a few coils and magnet wire spools and thought it might be fun to do the same. To my best recollection, my coils have no specifications so I was wondering how critical the capacitor sizing was.
No pic if you don't already have one. Sounds like you made a convenient gauss meter with what you had on hand. I have a few coils and magnet wire spools and thought it might be fun to do the same. To my best recollection, my coils have no specifications so I was wondering how critical the capacitor sizing was.
rsnell22
Member
- Location
- Western WA
I had the recorder set for 5% event threshold, and ran it for about 18 hours. No events triggered.
The only thing that indicated anything other than normal was a rise to 497 volts for about a minute, early in the morning.
I think that was just utility switching.
The new board came in, and the chiller is back to normal.
Haven't made any progress on the voltage to ground, other than I can't find any other transformers that could be the culprit.
Thanks again to everyone.
The only thing that indicated anything other than normal was a rise to 497 volts for about a minute, early in the morning.
I think that was just utility switching.
The new board came in, and the chiller is back to normal.
Haven't made any progress on the voltage to ground, other than I can't find any other transformers that could be the culprit.
Thanks again to everyone.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130419-0928 EDT
mivey:
At 72 mH it takes 98 ufd for 60 Hz resonance. So no resonant amplification at 60 Hz. But would be a problem around the 14th harmonic and those near by. A 98 ufd capacitor is sort of unwieldy.
An experiment with 90 ufd and the low Q of the coil did not result in much peaking.
A 1/2" dia. carriage bolt thru the coil center with 0.47 ufd approximately increased the voltage by 10 times with the same 10 A thru #12 and 1" away. Measured resonant frequency is about 490 Hz, and more peaking. When using a higher Q coil, as this is, it would be important to tune to 60 Hz.
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mivey:
At 72 mH it takes 98 ufd for 60 Hz resonance. So no resonant amplification at 60 Hz. But would be a problem around the 14th harmonic and those near by. A 98 ufd capacitor is sort of unwieldy.
An experiment with 90 ufd and the low Q of the coil did not result in much peaking.
A 1/2" dia. carriage bolt thru the coil center with 0.47 ufd approximately increased the voltage by 10 times with the same 10 A thru #12 and 1" away. Measured resonant frequency is about 490 Hz, and more peaking. When using a higher Q coil, as this is, it would be important to tune to 60 Hz.
.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130419-1034 EDT
mivey:
Testing with a separate excitation coil and close to constant input voltage. The coupling between the two different coils is different.
With the commercial flux probe and 0.47 ufd the resonant frequency is about 540 Hz and substantially peaked. An output of 0.7 at 60 Hz and 3.5 at 540 Hz.
The Warrick air core coil reads 2 at 60 Hz, 17 at 540 Hz, and 35 at 845 Hz.
I would need to do much more controlled experiments to draw any specific relative conclusions. Either coil with the 0.47 ufd capacitor is an effective tool to use for stray 60 Hz AC magnetic field detection.
.
mivey:
Testing with a separate excitation coil and close to constant input voltage. The coupling between the two different coils is different.
With the commercial flux probe and 0.47 ufd the resonant frequency is about 540 Hz and substantially peaked. An output of 0.7 at 60 Hz and 3.5 at 540 Hz.
The Warrick air core coil reads 2 at 60 Hz, 17 at 540 Hz, and 35 at 845 Hz.
I would need to do much more controlled experiments to draw any specific relative conclusions. Either coil with the 0.47 ufd capacitor is an effective tool to use for stray 60 Hz AC magnetic field detection.
.
Did any voltage surge damage the board? What is the surge withstand capability of the circuit board?
rsnell22
Member
- Location
- Western WA
Sahib,
I don't have any solid evidence of what took the board out. It is the ISM board on a 19XRV.
I wasn't able to get surge withstand info on the board.
There is a TVSS unit on the 480 side, but on another feeder. And a reactor on the feeder to the chiller.
There was some work done on the high voltage primary over the winter.
And some primary side problems about 18 months ago.
And there were other electronics failures in the building.
All in all, I can't prove anything.
I don't have any solid evidence of what took the board out. It is the ISM board on a 19XRV.
I wasn't able to get surge withstand info on the board.
There is a TVSS unit on the 480 side, but on another feeder. And a reactor on the feeder to the chiller.
There was some work done on the high voltage primary over the winter.
And some primary side problems about 18 months ago.
And there were other electronics failures in the building.
All in all, I can't prove anything.
Last edited:
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
I pulled up the PDF for the system (HERE) you listed and Carrier does design some very well engineered systems, we used some of their chillers in the past for hydraulic oil cooling at a aluminum extrusion plant but back then they were more of a relay logic control system then what we have available today.
In looking over the PDF I couldn't find anything restricting the chillers use on a ungrounded system, but it does have ground fault protection that is rendered useless on a ungrounded system and not used with the VFD version as the drive provides the GFP (FIG 57 in the pdf).
The ISA (integrated startup module) board is supplied from the 3kva control transformer that also supply's various other loads and control elements within the chiller, depending upon which options this chiller is being used it has either a 3 amp onboard fuse or a 1 amp fuse (3amp with VFD option), this board also does all the monitoring of the motors for current and ground fault (the ISM GFP is not used with a VFD) as well as under voltage and over voltage, but the voltage monitoring is through an open delta isolation transformer which would limit many type of faults that could damage the board except over voltage as this would be passed on through the transformer but should show up with damage to the voltage detection circuits of the ISM board, I do not see any kind of SPDs used on the input to this board or the 3kva transformer but this doesn't mean that they couldn't be onboard as this board doesn't have any board level component diagrams in the PDF which are most likely manufacture proprietary.
Without board level diagnostics to see what failed on the board it will be hard to say defiantly what was the cause, such as if the input (115 volt) section has damaged components then I would suspect that the board was over voltage, was the supply fuse (3 amp or 1 amp) opened? or did the board fail on the monitoring side such as the voltage detection side which would not allow the motors to start.
Is the unit under warranty from Carrier? or are you having to foot the bill? if you are footing the bill then if might be worth sending the board to Carrier to diagnose it at component level to see what took place, as if the problem with the service transformers did cause over voltage problems I would not be paying for something that was cause by others, with the fact that they experienced other electronic failures in the plant and if this boards failure was at the same time then I would be willing to say it was hit with an over voltage that should not be under any warranty.
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
130420-1622 EDT
mivey:
See PM I sent to you.
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mivey:
See PM I sent to you.
.
- Status