Looking for help with some Power Quality Reports

[iwire]

Hi all, I have two power quality reports I have produced and ... well ..... I need some help making sense of them.

I would be glad to hear any thoughts and I will answer any questions I can.

The reports are in Word.doc files and I had to place them at a file sharing web site, sorry you have to see some ads to get the download.

Thanks in advance for any help.

http://www.mediafire.com/file/f1p78jd7h8d5lip/Vilanova Report.rtf


http://www.mediafire.com/file/jg53cj1wx8i1l76/Hamlet Report.rtf

They are only about 3 MB each.

 

[iwire]

A little more background.

These reports are from two fairly large identical school buildings located within site of each other but are each independently supplied via a pad mount transformer out side of each.

The schools are fairly new and from what I am being told have been replacing a large amount of motors. We where asked to look into it.

Is 70 to 80 amps of harmonic current a lot with about 250 to 500 amps of load?

Why do the VHTD Timeplots show such regular patterns of rising and falling?

Do you think that just represent the electronic ballasts being turned on during the day and off at night?

What is flicker and should I be concerned about it?

I know, a lot of complicated questions in a short post.

Thanks,

 

[mayanees]

Bob,

A real quick review, real, real quick, and I offer the following observation:
I first go the the tolerance curve. I think it's labeled magnitude/duration curve, but it represents either ITIC or CBEMA compliance. The Vilanova file shows no deviations from that curve, but the Hamlet curve shows several hits below the curve. Those are problems that electronic type equipment wouldn't be expected to ride through, and even VFDs for that matter.
Both files show terrible power factors, which may offer areas for improvement. The Voltage and Current Distortion levels are relatively high, but really shouldn't provide problems for any given motors as long as the effective RMS value of current isn't tripping breakers.
It may be a case of oversized VFD-driven motors that are cycling excessively. I think that's where I'd start, at the larger VFDs in the system. Motors have poor power factors in the lower operating range, and if they're running real low, may not be cooling themselves off during a normal duty cycle.
Good Luck. I'm looking at something similar right now myself, but it's more from the school's apparent jump in energy consumption.
John M

 

[gar]

100823-0809 EST

iwire:

Why do you have to use the site where you located the files?

I went to the site. I have no idea where your file is or what are the unintended consequences if I click on something on the page that is displayed.

I am very gun shy of any site with that much unclear junk. The site is obviously intentionally deceiving.

.

 

[ghostbuster]

IWIRE

This is quite typical for a school,in recording studios the neutral current is almost 2 times the phase current


It could be ballasts or other mechanical equipment that is turned on during the day-V.F.D's etc.

 

[iwire]

100823-0809 EST

iwire:

Why do you have to use the site where you located the files?

Becuse I do not have a web server and the files are too big to upload to the forum.

I went to the site. I have no idea where your file is or what are the unintended consequences if I click on something on the page that is displayed.

You click the button at about the 2:00 position that says download.

I am very gun shy of any site with that much unclear junk. The site is obviously intentionally deceiving.

I do not see anything deceiving, they are not charging me to host my file so of course they are going to display ads.

 

[steve66]

Why do the VHTD Timeplots show such regular patterns of rising and falling?

My WAG would be that its caused by equipment turned on during the day. Lights, computers, copiers, printers, equipment with VFD's, etc.

Another WAG: I wonder if a lot of the voltage THD is caused by other utitlity customers? If not everyone in the area is on a delta to wye transformer, some of that could be coming in with the utility power.

 

[hurk27]

I'm seeing a very large brown out on 08/05/2010 about 15:00 hours, with a surge in current after this event, again on 08/09/2010 but in this case phase C is hit the hardest, with phase A almost as much with very little affecting phase B, might be some bad connections on the utility side?

on 08/01/2010 in the current time plots we can see where something was faulted on B phase by the jump in current in both the neutral and B phase?

 

[iwire]

No doubt there was an outage in the Hamlet report, I was really not concerned with that.

Mostly I was wondering if anyone saw something that could be causing motor failures.

 

[ptonsparky]

No doubt there was an outage in the Hamlet report, I was really not concerned with that.

Mostly I was wondering if anyone saw something that could be causing motor failures.

Hmmmm....I wonder

 

[gar]

100824-1028 EST

iwire:

What has failed in the motors? Insulation breakdown or windings opening? Are all windings equally damaged? I am assuming the failures are not mechanical, meaning bearings.

Do all failed motors fail in the same way?

What might be common between the failed motors? Are they all VFDs or in some way controlled with electronics? In this case meaning there are power semiconductors in series with the motor windings. What about ambient temperature commonality?

Are any standard induction motors with standard mechanical contact contactors in the group of failed motors? Standard induction motors are extremely reliable, even with moderate changes in supply voltage. Maybe wptski can provide you with some experience on motor failures at Ford Sterling. My guess is that they have few thousand motors in that plant.

I quickly looked at your Vilanova data.

On "Voltage Timeplots" B Vrms shows a large down spike before noon on 8-11-2010 and a slight up spike on A Vrms. These are likely correlated. Most of this is a B phase problem.

On "Flicker (PLT) Timeplots" at about noon + all three phase show a large flicker pulse. Looks correlated. A small down spike shows on all three voltage plots st this time.

Nothing is obvious that would cause standard induction motors to fail.

.

 

[ptonsparky]

What is "flicker" as used with these reports?

 

[mxslick]

Bob, I think the harmonics you recorded as well as the low power factor may be the root of the problem. I'm not a motor expert though so I am not sure how/if those factors would affect motor life.

As for the "outage" noted in the Hamlet report, that could be attributed to a short circuit from one of the motor failures perhaps?

Interesting reading in any event, thanks for sharing them and I hope that someone here can get you the answers you seek.

 

[IslandSparky]

Motors not on VFD are a sink for harmonic voltage. When the motor shuts off, Vthd increases if current sources persist. Can't view the graphs, but look at your harmonic profile and see if you are richest in 3rd or 5th/7th. A phase-shift transformer can then be selected to help cancel some of the internal harmonics. 3rd harmonics should be all internal, but 5, 7,11,13 could be external.

Motor failure can be attributed to excessive harmonic heating of the stator.

 

[AdrianWint]

I can't view the reports, but a thought....

Look for even order harmonic voltages (2nd, 4th etc) these are negative sequence and when they hit a direct connected motor, they create a torque which is in opposition to that created by the fundamental. If these are large enough, you can get to the silly situation where the motor is overloaded with only a small mechanical load

Just my two penny worth!

Adrian