[RE-wrenches] Strange voltage readings, power quality

[Darryl Thayer]

jm7 y first thought is a bad neutral connection, it could be heavy neutral current do to harmonics,  The grow lights put a load on the neutral by third harmonic.  I have seen a switch gear burn up after we put the school on electronic balasts.  
Darryl


________________________________
From: Nathan Jones <solardude97 at yahoo.com>
To: re-wrenches at lists.re-wrenches.org
Sent: Sunday, November 13, 2011 3:12 PM
Subject: Re: [RE-wrenches] Strange voltage readings, power quality

Mac,
I have encountered two battery based inverters that were affected by the feedback frequency of CF bulbs. One would trip and show overload from a single 15 watt bulb with no other loads connected every time. The other one was an intermittant situation. Had I not encountered this problem before I might still be trying to figure that one out. I think it would be worth ruling out as a possibility at this point.
Nathan Jones
Power Source Solar
417-827-0738
On Sun, Nov 13, 2011 10:55 AM CST mac Lewis wrote:

>Hello wrenches,
>
>I am having an interesting grid-tied issue and would love to get some input.
>
>The installation is 3 Fronius IG Plus inverters all single phase, two 7.5s
>and one 10.0.  The service is 120/208.  We have the two 7.5s feeding a
>dedicated 3 phase sub and tied back into the main panel after production
>meter.  The first 7.5 is tied across Va to Vb, the second is tied in across
>Vb to Vc.   The 10.0 feeds directly back to the main panel after production
>meter and is tied in across Va to Vb.
>It should be noted that this facility has very large capacitive load, about
>25 kW of grow lights.  According to an egauge on site, the power factor
>ranges from 0.5 to 0.75 on all phases.
>The system worked flawlessly for 3 months, suddenly the two 7.5s dropped
>out and gave a myriad of grid errors, everything from islanding errors, to
>high grid voltage, and low grid voltage etc.
>
>I went over there and found the phase B voltage to neutral, was way out of
>wack, anywhere from 120-170.  Oddly, the Line to line voltage was fine,
>right around 208 for all phases.  I called the power company and had them
>install a monitor at the transformer.  After 5 days they came back and said
>that their end was within spec.  I decided to put both of the 7.5s between
>Va to Vc.  They would not boot up.  I then went to the main panel and
>changed the physical location of the breaker for the subpanels of the 7.5s.
> This seemed to make the difference.  They booted up and are exporting
>power.  I tried switching one of the 7.5s back Va to Vb, but it still would
>not boot up unless it is connected from Va to Vc.
>
>My working theory right now is that we are getting harmonics traveling back
>to the inverters from the ballasts on the grow light across line B.  As far
>as explaining why it suddenly happening, my guess is that he has started
>turning off inductive loads such as fan motors and compressors as we are
>entering the winter.  There may have been a filtering effect going on with
>the motors absorbing some of these harmonics and attenuating them.  I am
>going to try to verify this with an oscilloscope this week.
>
>Does anyone have any other theories to explain this type of behavior?
> Anyone seen this before?  Should I look for anything else?
>
>Thanks
>
>Mac Lewis
>
>
>-- 
>
>
>
>Mac Lewis
>
>*
>
>"Yo solo sé que no sé nada." -Sócrates
>*

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