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Author Topic: Solar Panel (Grid-tied) System and EMI / RFI  (Read 15472 times)
WX7G
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Posts: 6218




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« Reply #15 on: October 19, 2013, 08:08:22 AM »

...it's been my experience that grid power is dirty and runs anywhere between 55-65hz and 95-130vac. At least that's what I measured when I was a PG&E and SoCal Edison subscriber.

I think you had a substantial power grid frequency measurement error. The power grid in Arizona is tied directly to California and New Mexico which are tied into the rest of the Western U.S. There can be no local frequency changes and the frequency is maintained within about 0.02 Hz short term. In the long term the frequency averages to exactly 60 Hz so that clocks are accurate.

http://en.wikipedia.org/wiki/Utility_frequency#Long-term_stability_and_clock_synchronization

Here is a real-time map of U.S. AC power frequency.

     http://fnetpublic.utk.edu/gradientmap.html
« Last Edit: October 19, 2013, 08:18:09 AM by WX7G » Logged
KG7BGZ
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Posts: 2




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« Reply #16 on: October 20, 2013, 04:32:51 PM »


I think you had a substantial power grid frequency measurement error. The power grid in Arizona is tied directly to California and New Mexico which are tied into the rest of the Western U.S. There can be no local frequency changes and the frequency is maintained within about 0.02 Hz short term. In the long term the frequency averages to exactly 60 Hz so that clocks are accurate.

http://en.wikipedia.org/wiki/Utility_frequency#Long-term_stability_and_clock_synchronization

Here is a real-time map of U.S. AC power frequency.

     http://fnetpublic.utk.edu/gradientmap.html

A couple things here:

Notice that I said that I'm off-grid in Arizona. I've never dealt with APS, so I wouldn't know how reliable their service is on a personal level.

I am acutely aware the power for the WAPA Desert Southwest and WAPA Sierra Nevada districts (the areas I lived) come from. And I am also acutely aware of how it all works.

Sure, power is supposed to be 60hz within an extremely small tolerance. But, as I said, I have found that it is not always clean and not always at ~60hz. In the areas I lived "Sags", "Swells", "Rolling Brown Outs" and "Transient Impulses" were/are very common and cause a wide variation in the frequency of the power. And they happened quite a bit, every single day. PG&E and SCE say they only occur for milliseconds. But, the University of California has data that shows otherwise. This study from the University of California (LBNL) documents that there are many sustained frequency variations in the national grid. In fact, you'll see that there are documented deviations that were sustained for periods of one minute or more. http://www.nerc.com/FilingsOrders/us/FERCOrdersRules/Interconnection_Frequency_Performance.pdf. Maybe my measurements were wrong but the fact that PG&E and SCE both say that their variations are just "occasional" and only last "milliseconds"  while UC Berkley has documentation that shows hundreds of these variations lasting one-minute or more, I'm not convinced.

Of course, there was an article in 2011 that reinforced my observations that grid power is dirty. And it used clocks in various areas as an example of the deviation, pointing out that some of them are as much as 40-minutes off. It was an article about allowing a proposed year-long experiment to allow wider variation in grid frequency. That article is here: http://www.washingtontimes.com/news/2011/jun/24/ap-exclusive-power-grid-change-may-disrupt-clocks/?page=all

I realize that you said nothing about the other quality issue I mentioned, voltage being delivered to the customer but I thought I'd also address that. Conservation Voltage Reduction is quite real. The utilities (at least in California) reduce the power provided to homes. It's only supposed to be a ~5% reduction, but, again, I saw voltages much lower than a 5% reduction over very long periods of times extended periods of times. The utilities will say it's a misconception that CVR will not damage appliances, and it probably is true if the reduction is ~5%, but I experienced reductions in the 12% range. Does this cause interference? I don't know but I'd bet that it causes other devices to run at less than optimum performance, potentially causing interference.






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KO7I
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Posts: 106




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« Reply #17 on: October 26, 2013, 12:29:51 PM »

Don, I bet you work at Northwest EMC. When I worked I Micron I took several pieces of in-house test equipment to the Oregon NW EMC for testing.

After doing commercial EMC at Micron Technology for a number of years I did Military EMC for five years. I now do consulting and my specialty is EMC filter design. I'll be installing solar panels on my RV next year and look forward to taming the expected EMI issues.

I work for CKC Labs (ww.ckc.com). My specialty is MS-461 & DO-160. After getting our lightning lab up and going, I moved on to HIRF.  We are about to go online with a reverb chamber (by ETSL) using a 2kW 80-1000MHz amp by AR & 4kW TWT's by CPI covering 1-18GHz, We chose NEXIO Bat-EMC as the control SW. We will be able to reach 3,500V/m with 12dB of chamber loading. I doubt we will ever go to MS-464 HIRF, the required amps in dB $$ are cost prohibitive.
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