Power Quality Analyzation

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Greg Swartz

Greg Swartz

Senior Member
Location
Colorado Springs, Colorado
Anyone here ever perform Power Qualify Analyzation?

We were referred a client today, that has some potential power quality issues.
I know basic power quality analyzation techniques, but am wondering about the indepth stuff, and what you did in such a situation.

I have no problem taking this to PM or e-mail or phone.

Thanks,
Greg
 
Issues...

Issues...

The tenant has 8 or so rack mounted servers, and another 15-20 high end desk top computers. All high grade stuff. Not Best Buy quality.
Everything is hand made.

They move into the property, and every 6 weeks to 3 months, they blow a power supply, which leads to more failed parts. This last time, there was a complete RAID system that failed. ($$$)

Every computer is on it's own dedicated circuit to the panel.
Every computer is on it's own UPS. Ususally APC 1500VA systems.

There are other tenants in the building, but none of them have this problem.

I think... personally... that there are large harmonics due to the computer usage... but I cannot substantiate that, until I come out to check.

I gave the guy a price to come and check it out, but he told me he'd get back to me in 3-4 WEEKS... :roll: ... I imagine the last hard drive crash / replace / recover should cost 2x my price alone!

Thoughts?
 
Greg Swartz said:
The tenant has 8 or so rack mounted servers, and another 15-20 high end desk top computers. All high grade stuff. Not Best Buy quality.
Everything is hand made.

They move into the property, and every 6 weeks to 3 months, they blow a power supply, which leads to more failed parts. This last time, there was a complete RAID system that failed. ($$$)

Every computer is on it's own dedicated circuit to the panel.
Every computer is on it's own UPS. Ususally APC 1500VA systems.

There are other tenants in the building, but none of them have this problem.

I think... personally... that there are large harmonics due to the computer usage... but I cannot substantiate that, until I come out to check.

I gave the guy a price to come and check it out, but he told me he'd get back to me in 3-4 WEEKS... :roll: ... I imagine the last hard drive crash / replace / recover should cost 2x my price alone!

Thoughts?
Click to expand...

I'll bet his neutrals are cooked and you can measure several volts from his neutral to ground at the computers.

It's funny the Code allows a reduced neutral but with the advent of computers (non-linear loads) 200% neutrals are becoming the "in" thing.

We had a medical clinic that fried a computer or server everytime a black cloud came over but they didn't have any money for correcting the "cause" of the problem.
 
Another thing to check is if it supplied by an isolated ground, that it is properly grounded. I have seen many Isolated ground bars that are so isolated that they didn't ground it at all!:rolleyes: Since the Isolated ground bar is insulated like a neutral bar, if no ground is taken back to the service the equipment is effectivly ungrounded. I have seen "electricians" take the ground to a sole ground rod, thinking thats what "Isolated Ground" means!
 
that is a funny story Hillbilly. I had a guy (computer engineer) ask me to do exactly that once. But the equipment should not even be using the GEC at any time, except for a short.

My money is on harmonics, since they would eventually overtax the PSU.
 
I'm assuming that this was thought of before, but it is worth checking...

Is it always the same power supply or is it a different power supply every time? Has the same power supply failed 2 or more times since they have been at that location?

What about the area/room that the equipment is in? Is it sufficiently ventilated and/or cooled? Are the power supplies/servers in electrical enclosures or are they simply on a free standing metal rack? If they are in electrical enclosures, are the enclosures ventilated, and if they are, do the vent openings have filters on them (you would be surprised at how infrequently people change filters).

These are a few questions that should be answered or given thought to before it is automatically assumed that it is a PQ problem. I have seen MANY power supplies and VFD's fail simply because of insufficient cooling/ventilation. Sometimes the same power supply or drive has failed at least 2 times before anyone thought about ventilation.

As I said, I am assuming that was thought of already, given the fact that they have this much expensive equipment, but it doesn't hurt to check!
 
Check voltage at the panel.
Check the voltage at the loads.
Check neutral and all phase currents you can determine if harmonics are high based on this.
Measure zero sequence currents on all phases and neutral
Check the current at the neutral to ground bond.
Check for neutral issues in the panel and upstream of the panel.
Look for the always noted loose connection.

Last 3 times we had this happen the manufactures finally admitted defective power supplies.
Time before that it was whiskers.
One time it was excessive dust dirt blocking cooling.

If they have one item in particular causing problems get a double conversion (true UPS) to isolate the issue.

Isolated ground or not should make no difference.

I'd bet on the manufactures.
 
Greg Swartz said:
The tenant has 8 or so rack mounted servers, and another 15-20 high end desk top computers. All high grade stuff. Not Best Buy quality.
Everything is hand made.

Every computer is on it's own UPS. Ususally APC 1500VA systems.


I think... personally... that there are large harmonics due to the computer usage... but I cannot substantiate that, until I come out to check.

Thoughts?
Click to expand...

All high grade stuff / hand made? I would think the designer/manufacturer of this stuff would be interested in doing a failure analysis of their quality stuff that is failing so frequently.
Such an analysis could help point to the cause.

Have they been asked about the possibility that their equipment might fail due to high harmonics? If each computer is on its own UPS I would not suspect harmonics (at the computer loads) to be at issue?

If I am remembering correctly the output of a lot of APC UPS's have their neutral floating with respect to Earth gnd.
 
ELA said:
All high grade stuff / hand made? I would think the designer/manufacturer of this stuff would be interested in doing a failure analysis of their quality stuff that is failing so frequently.
Such an analysis could help point to the cause.

Have they been asked about the possibility that their equipment might fail due to high harmonics? If each computer is on its own UPS I would not suspect harmonics (at the computer loads) to be at issue?

If I am remembering correctly the output of a lot of APC UPS's have their neutral floating with respect to Earth gnd.
Click to expand...

Great questions for the mfg. but don't be surprised if they don't own up to a problem. The answers you receive will probably come from their legal dept. not eng.
 
ELA said:
All high grade stuff / hand made? I would think the designer/manufacturer of this stuff would be interested in doing a failure analysis of their quality stuff that is failing so frequently.
Such an analysis could help point to the cause.
Click to expand...

ARE YOU CRAZY, if they know there is a defect then they have to implement a recall and replace ALL defective components, if the keep it under wraps then it is a onesy twosy thing.


Have they been asked about the possibility that their equipment might fail due to high harmonics? If each computer is on its own UPS I would not suspect harmonics (at the computer loads) to be at issue?
Click to expand...

Typically they do not ask they blame grounding then harmonics.

If I am remembering correctly the output of a lot of APC UPS's have their neutral floating with respect to Earth gnd.
Click to expand...


When on battery, I think this may be the case. On utility the UPS is doing nothing.
 
Considering each unit has it's own UPS and the power supplies are failing while other tenents have no problems--they have a batch of bad power supplies. Of course the manufacturer and/or supplier is pointing fingers at the building. The UPS is designed to prevent any possible damaging voltage to reach the device it is protecting. But we always installed our data loggers and provided documentation to make them happy and it's easy work:D
 
brian john said:
Check neutral and all phase currents you can determine if harmonics are high based on this.
Measure zero sequence currents on all phases and neutral
Check the current at the neutral to ground bond.
Check for neutral issues in the panel and upstream of the panel.

Time before that it was whiskers.

If they have one item in particular causing problems get a double conversion (true UPS) to isolate the issue.
Click to expand...

Could you please explain what all that means?
 
charlietuna said:
Considering each unit has it's own UPS and the power supplies are failing while other tenents have no problems--they have a batch of bad power supplies. Of course the manufacturer and/or supplier is pointing fingers at the building. The UPS is designed to prevent any possible damaging voltage to reach the device it is protecting. But we always installed our data loggers and provided documentation to make them happy and it's easy work:D
Click to expand...

2/3s of the time this is the case or was that 3/4ths. But you have to prove it is not a PQ issue.
 
Last edited:
Greg Swartz said:
The tenant has 8 or so rack mounted servers, and another 15-20 high end desk top computers. All high grade stuff.
...
Every computer is on it's own UPS. Ususally APC 1500VA systems.
Click to expand...

The comments above make me wonder about the logic of their design.

Why in the world would you spend the money to buy individual line interactive UPS's? For the money they spent they could have bought a larger dual-conversion UPS to power all of the equipment and clean up the power at the same time instead of having many static switched battery backup sources that all require battery pack replacements every 4 years (or less). I think calling all of the 120V APC UPS's uninterruptible power supplies is pretty deceiving - I'm amazed the industry still uses the term UPS for line interactive units.

A return-on-investment analysis on the battery maintenance of many small units may be enough to justify a larger, higher quality unit. A large stationary battery bank can be serviced and will last 15 years as opposed to replacing many small packaged battery packs every 3-4 years.
 
ohm said:
I'll bet his neutrals are cooked and you can measure several volts from his neutral to ground at the computers.

It's funny the Code allows a reduced neutral but with the advent of computers (non-linear loads) 200% neutrals are becoming the "in" thing.

We had a medical clinic that fried a computer or server everytime a black cloud came over but they didn't have any money for correcting the "cause" of the problem.
Click to expand...
I told the owner that there could be a problem with the neutrals.
I also explained that due to high harmonics, the transformer may need to be replaced (with a K type).

hillbilly1 said:
Another thing to check is if it supplied by an isolated ground, that it is properly grounded. I have seen many Isolated ground bars that are so isolated that they didn't ground it at all!:rolleyes: Since the Isolated ground bar is insulated like a neutral bar, if no ground is taken back to the service the equipment is effectivly ungrounded. I have seen "electricians" take the ground to a sole ground rod, thinking thats what "Isolated Ground" means!
Click to expand...
IGs are over rated (no pun intended)... I believe if we (electricians) do our job correctly, there should never ever be a need for IGs.
Just a personal belief.

eric7379 said:
I'm assuming that this was thought of before, but it is worth checking...

Is it always the same power supply or is it a different power supply every time? Has the same power supply failed 2 or more times since they have been at that location?

What about the area/room that the equipment is in? Is it sufficiently ventilated and/or cooled? Are the power supplies/servers in electrical enclosures or are they simply on a free standing metal rack? If they are in electrical enclosures, are the enclosures ventilated, and if they are, do the vent openings have filters on them (you would be surprised at how infrequently people change filters).

These are a few questions that should be answered or given thought to before it is automatically assumed that it is a PQ problem. I have seen MANY power supplies and VFD's fail simply because of insufficient cooling/ventilation. Sometimes the same power supply or drive has failed at least 2 times before anyone thought about ventilation.

As I said, I am assuming that was thought of already, given the fact that they have this much expensive equipment, but it doesn't hurt to check!
Click to expand...
There are multiple PS that have failed, on multiple circuits. Again, each circuit being a HR back to the panel.
The servers have blown PS and the server room a 4' x 4' closet has serious venting... it will close the door on you... I already asked that.
The desktop / workstations have had power supplies fail as well. However, not as often.

brian john said:
Check voltage at the panel.
Check the voltage at the loads.
Check neutral and all phase currents you can determine if harmonics are high based on this.
Measure zero sequence currents on all phases and neutral
Check the current at the neutral to ground bond.
Check for neutral issues in the panel and upstream of the panel.
Look for the always noted loose connection.

Last 3 times we had this happen the manufactures finally admitted defective power supplies.
Time before that it was whiskers.
One time it was excessive dust dirt blocking cooling.

If they have one item in particular causing problems get a double conversion (true UPS) to isolate the issue.

Isolated ground or not should make no difference.

I'd bet on the manufactures.
Click to expand...
1. I have those items noted. I was going to use a PQ monitor and log the data at the panel. Then download the data and look for spikes / sags and excessive neutral current.
2. Good idea on the loose connection.
3. At this rate, I think the guy will let a few more PS go before he hires us.

charlietuna said:
Considering each unit has it's own UPS and the power supplies are failing while other tenents have no problems--they have a batch of bad power supplies. Of course the manufacturer and/or supplier is pointing fingers at the building. The UPS is designed to prevent any possible damaging voltage to reach the device it is protecting. But we always installed our data loggers and provided documentation to make them happy and it's easy work:D
Click to expand...
I agree that it would be easy work. We could make a good profit on the job. What's a good price to perform data logging for 24 hours... and then interpret the data for them?
 
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