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Thread: POCO issue or not?

  1. #1
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    POCO issue or not?

    5 day recording by poco for 120/240 1ph resi.

    poco tells me they run by ANSI C84.1 (i assume range A)

    under C84.1 is it supposed to be 120 nominal, at least once? this chart shows ~124 nominal.

    but i'll ask, does ANSI C84.1 just provide a min/max range, or does it also spec that nominal should be 120v with the allowance for fluctuation to min/max ?

    this chart does not look to me to be complaint with C84.1. I rather sure it went above 127v at least once, but poco says "all looks ok".

    what say you?


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    Looks okay, perhaps something changes due to weather, wind, neigbors neutral, etc... What's the reason for the test?

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    190613-1952 EDT

    FionaZuppa:

    What is the definition of "nominal"?

    The following is from https://www.merriam-webster.com/dictionary/nominal

    See 3 b.

    In other words the design criteria is for 120 V.

    The recordings show a somewhat instantaneous set of values, actually short time average values. Looking at the charts the overall daily average is about 124 V. This is the output of a nominal 120 V supply. Very typical.

    Nominal and average do not mean the same thing.

    You need to look for some other criteria than nominal to determine if power company meets its obligations. Somewhere a definition of a short time average time period is needed.

    .

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    Quote Originally Posted by Buck Parrish View Post
    Looks okay, perhaps something changes due to weather, wind, neigbors neutral, etc... What's the reason for the test?
    Voltage dips & spikes (i suspect spike) are causing a APC UPS to trip on for short period. This happens 3-7x weekly.

    The 127v seems a bit high though, that's the max under the ANSI spec.

    I'll dig out my DATAQ 16kHz recorder to see what I can find, I don't think poco recorder is of any good type.

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    190613-2414 EDT

    FionaZuppa:

    I don't know if UPSs trip on spikes, usually it is dips. I also don't trust power company recording, from experience, unless I really know something about their recorder.

    I believe APC UPSs have data output that provides time information on transitions. Requires a serial port data collector.

    With an old model TED 1000 I can record line voltage with 1 second, and 0.1 V resolution. See my plot PE1 at http://beta-a2.com/energy.html . Also see plots P29 and P30 at http://beta-a2.com/EE-photos.html . These last plots are at the end of a long branch circuit, not at the main panel. The other plots were at the main panel.

    Note: newer versions of TED do not provide 1 second resolution even though their implication is 1 second.

    .

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    120 volts is nominal- which basically means a certain min or max range that can not be exceeded. In reality it will vary between 115 to 127 if not more. Sometimes it will be continuously above or below 120, other times it will yo-yo throughout the day or year.

    Be happy, in a lot of other parts of the world is varies more than +- 10%.


    Considering just how much goes on in a power system from ferrarenti rise to switching lines out to power factor compensation to I2R which is in every wire and piece of equipment no matter the size its a miracle you can get a +- 10% bandwidth let alone +- 3%.

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    I recommend you read these, highly educational.


    Of note, transmission and sub-transmission voltages will vary + or - 5% of nominal for many complex reasons and sometimes will vary + or - 10%.




    https://beckwithelectric.com/wp-cont...pp-Note-17.pdf


    https://beckwithelectric.com/wp-cont...pp-Note-29.pdf


    https://beckwithelectric.com/wp-cont...-App-Tip-2.pdf


    Caps also regulate voltage on the distribution and transmission levels:


    https://beckwithelectric.com/wp-cont...-App-Tip-4.pdf



    All can be found here:

    https://beckwithelectric.com/app-notes/



    Typically under peak demand the substation tap changers will keep the distribution bus voltage at +5% of the 12.47kv nominal as the 115kv transmission voltages varies +or- 5%.


    This is so customers at the start of the 12.47kv feeder will have 126 volts, 120 at the middle of the run, and 116 at the end of the run.


    If the voltage at the end dips below 116 volts, POCOs will add cap banks or voltage regulators or both to correct and boost this voltage. With voltage regulators you can boost the 116 volts at the end to 126 volts basically starting the process over again increasing the length a feeder can travel.



    Switching schemes like picking up load that was served by another feeder or substation can cause the voltage to dip below 115, 110 is not unheard of during emergency restoration switching after a car brings down a pole.


    With that said when load dips at night or during the spring/fall its not energy efficient to keep the feeder voltage at +5% since due to the reduced voltage drop along the 12.47kv feeder most of the customers will see 126 volts and those at the end might see 124 volts. Typically anything fed above and below 120 will be less efficient and things like light-bulbs will burn out much faster above 120. So you get into line drop compensation. As the load decreases at the substation the tap changers only maintain +3% or +1.5% at the substation buss. That way customers at the start of the run will see 121.5 volts, 120 in the middle and 119 at the end. Like this the total customer median/mode voltage is 120 throughout the year under all loading conditions.

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    1) the APC UPS has it's own recording software, but it only records what caused the event as "low" or "high", and the UPS itself can be set via software for min & max, which is set properly. My DATAQ data acquisition device & software will datalog at 16kHz, which is way better than the poco device.
    2) This problem is not new, had it years ago, then it went away, now it's back. Was told back then that the hv feeder also feeds local cement plant and that we get ringwave spikes/dips due to plant turning on heavy motors, and, that the switching gear is old and antiquated.

    I am well versed with this poco and their power issues, I was just trying to see if their "looks ok to us" statement jives with the chart they provided.

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    Don't APC UPSs have a 'sensitivity' setting? I don't remember what it's sensitive -to-, but might be worth a look.

    My power regularly >glitches< about 4 Saturday afternoon (maybe every afternoon, but I'm not home). My APC may gurgle a bit; I don't recall it actually 'running.'

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    190514-1425 EDT

    FionaZuppa:

    On the surface the power company plot does not show a problem, but their averaging time per point may be too long.

    You will need to run your own tests.

    My comment on the APC data output was that it provides timing information on when events occur which would make it easier to look for a glimpse of what is happening at very isolated times in the power company plot.

    .

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