My understanding is anything over 5% THD is getting to be a problem.
I've measured that high on grid here before. Do you have any idea what
harmonics this distortion is at? Have you looked at it on an O scope?
What generator is this? I've seen portable generators with terrible
wave forms under load. They have a front end spike on the waveform, and
then they flatten out under load. Anything that isn't a pure sine wave
is distortion.
Have you checked the peak of the wave form? I've seen generators under
load, flatten to 135 v peak, which is really not even a sine wave
anymore. Very poor performance, most AC electronics do not like a DCish
wave form.
Also, I have a Seaward meter that does THD, its a little clunky to
navigate, but it gives real time readings, is battery powered, and can
break out the separate harmonics too. The harmonics just give you an
idea at what frequency the distortion is at, which "might" let you
figure out what is causing problems. I don't know enough about AC GFI
electronics to know what effect THD would have, but 19% THD is total
trash, and all bets are off; it could damage all sorts of other
equipment too.
I think you've already done all that needs to be done: They need a
better generator.
Ray Walters
Remote Solar
303 505-8760
On 1/23/20 1:16 PM, William Miller wrote:
Colleagues:
In a recent post about some AC GFI tripping problems, I mentioned I am
measuring some high THD readings in certain scenarios—the highest
being when the generator is charging at high percentages:
Inverter only: 2.5% THD
Gen Max: 19% THD
Gen 5 Amps: 8% THD
I measured the THD using a Fluke VR1710 <TJ3fTpspG2DGCzC>. This is a
handy little gizmo and pretty expensive considering its size. The
device has limitations:
1.It is cord connected.
2.Results cannot be viewed in real-time.
3.It measures voltage parameters only.
Here are my questions:
1.Has anyone here had to consider problems with high THD in any
off-grid scenarios?
2.What readings are normal?
3.What is the significance of voltage harmonics versus current harmonics?
4.What instruments are you using to measure THD?
5.Has anyone seen high THD causing AC GFI tripping?
6.What other symptoms might occur with high THD?
Tip: The reason we first started suspecting high THD is that cheap
voltmeters registered abnormally high (including the onboard Radian
metering) during periods of high THD, while true RMS meters (Fluke 87)
continued to measure normal AC voltages. If you experience this
situation, high THD is suspect.
Answers are always gratefully appreciated.
William Miller
PS: If you are receiving a BCC of this email, it is because you are
part of the team working on this problem. The message is directed to
an industry forum in hopes of gleaning additional knowledge. I will
share any results I receive.
Wm
Miller Solar
17395 Oak Road, Atascadero, CA 93422
805-438-5600
www.millersolar.com <http://www.millersolar.com/>
CA Lic. 773985
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