[RE-wrenches] Quantifying power quality

[Starlight Solar Power Systems]

Hi William,

If you recall a couple years ago we had some discussion here about a problem with a specific make appliance being powered by a Magnum inverter. The problem, it was discovered, was the appliance input PF was creating current demands that the transformer based inverter could not keep up with. When I powered the load with a low cost, high frequency inverter, it worked fine. Apparently the HF inverter can keep up with the current changes faster than the Magnum.

To fix the problem, a 50mf run type capacitor was installed in the appliance so that it was applied across the AC input when powered on. Everything worked fine then because the cap was taming the wild current created by the low PF. 

Try looking at the current and voltage waveform together (AC shunt, dual trace scope) at the UPS input. If the current is displaying large spikes and/or is out of phase, you may have found the problem is with a non linear load from the UPS. It may be the SI, like the Magnum, can not keep up and so the UPS input circuits are throwing a fit.

Or, something else you can try, connect a high frequency inverter and try to power the UPS. This can be a portable 12 volt battery and inverter. If the problem disappears, well, you take it from there.

Larry



On Oct 11, 2014, at 11:21 PM, William Miller <william at millersolar.com> wrote:

Friends:
 
I am still having a pi$$ing match with the company that installed the expensive home entertainment system for a client over the issue of power quality.  The UPS beeps frequently and the AV system crashes now and then.  The lead installer has copped an attitude and is blaming the Sunny Island / Sunny Boy / Generac system for the AV system problems.  The UPS emails reports in flurries that indicate a “power failure” has occurred. 
 
I have a Dataq data acquisition system sampling at a rate that allows me to see the individual cycles on the system output on one of three phases.  During the time that a power failure is reported to have occurred each and every cycle looks great.  I know this is not a definitive test of power quality so I upped my game.  I bought a Fluke VR1710 power monitor and I am recording power quality from the same receptacle that feeds the UPS.
 
I have some log files from the Fluke Power Log software but the instructions are not that great and I don’t know how to interpret the data.  Do any of you have any experience with this software and could possibly advise me?
 
In a more general sense, how good is power to be called “good”?  I have done some research and the industry material is a bit overwhelming.  Does anyone have a short answer?
 
And lastly, even though the UPS is beeping, if it is doing what it is designed to do, the power quality should not be an issue because the UPS corrects for any problems.  (Actually the UPS was beeping—the best move in this situation was to mute the annunciator so at least the homeowner is not hearing the beeper.)
 
I know others of you are dealing with the same problems because it came up on this forum.  I am interested in an approach that verifies the Sunny Islands are producing adequately good power, or not, so I can either address the problem or get the AV guy off my rear end.
 
Thanks in advance.
 
William
 


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