unbalance 110 loads and the electric meter.

solar_dave
solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
How does the meter work when loads are unbalanced between the 2 110 legs.

Comments

  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    Re: unbalance 110 loads and the electric meter.

    If you are talking the utility meter. Will work just fine.

    My loads are like 75-25.
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: unbalance 110 loads and the electric meter.
    n3qik wrote: »
    If you are talking the utility meter. Will work just fine.

    My loads are like 75-25.
    Are you connected to a smart meter. I live in Pa. too and they have started installing smart meters. There is a monthly charge on my bill for the smart meter. I think they are working into time of day metering eventually in Pa. Solarvic
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
    Re: unbalance 110 loads and the electric meter.

    Not yet. PECO is doing a test install in Chester County. Everyone will get a new meter by 2015.

    How much is this monthly charge???
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: unbalance 110 loads and the electric meter.

    Watch the meters closely--especially in hot weather--They had to change out a bunch of smart meters and give refunds last year that read high (2x?) during hot weather.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
    Re: unbalance 110 loads and the electric meter.

    Ken on my last bill there was a smart meter charge for $1.05. Penn Power whose parent is First Energy. My understanding that will be charged till the meter is paid for.
    Bill How can you tell if the meter is working correctly? I have kept all my electric bills since a year before I commisioned my solar system. Seems that power co is having trouble figuring my bill as it always has white out where they typed in the figures. A friend that has a solar system says his bill always has whiteout too. Even though my neighbor gets thier meter read the same time my bill comes at least a week later than thiers. Solarvic
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: unbalance 110 loads and the electric meter.

    That is the $400 per month question... I read that one utility tech simply plugged in one or two electric heaters for 1/2 hour or so and saw what the meter read while the rest of the house was turned off.

    In a few cases, the utility installed a second socket and plugged in an old mechanical meter.

    In my case, I compare my GT inverter output vs what my meter shows (it has a kWH register). And I know that my home typically draws 100-400 watts with background loads So it is easy to see 3kW from my inverter and 2.7 kW from my utility meter.

    Basically, I would just keep a watch on your year over hear bills--If they double, there is a chance something is going wrong--But so far, it has been difficult to convince the utility there is a problem (testing shows everything is OK--but people complain about very high summer electric bills--in hot weather regions where some meters appeared to fail to log correctly when hot).

    There are also, apparently, com link errors too that have shown up in bills (meters dump readings over their wireless network every 15 minutes to 1 hours; business/residential as I understand for our area).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • solar_dave
    solar_dave Solar Expert Posts: 2,397 ✭✭✭✭
    Re: unbalance 110 loads and the electric meter.

    I guess my question is better stated, how does the meter handle the legs with differing loads? If each leg on a smart meter is measured then added and divided by 2 seems to make sense.
  • russ
    russ Solar Expert Posts: 593 ✭✭
    Re: unbalance 110 loads and the electric meter.

    That is what I am told is done except mine is three phase.

    I have four meters with one as a master (the official one) - everything seems to add up.

    The smart meters have a draw of their own - you never would see it if there is any other consumption but about 190 watts every two weeks or so. Doesn't seem regular.

    Russ
  • Jburgess
    Jburgess Solar Expert Posts: 130 ✭✭✭
    Re: unbalance 110 loads and the electric meter.
    solar_dave wrote: »
    I guess my question is better stated, how does the meter handle the legs with differing loads? If each leg on a smart meter is measured then added and divided by 2 seems to make sense.

    For a residence they usually measure the sum of the two 120 volt legs with one current transformer (element), so meter can’t tell the difference between 50 amps on both legs or 100 amps on 1 leg.
  • Ravs
    Ravs Registered Users Posts: 13
    Re: unbalance 110 loads and the electric meter.

    Solar Dave-

    The utility meter reads both legs of the service and totalizes the KWH, not amps. you could actually be selling power on one leg, and purchasing power on th other if your loads are unbalanced in your house.
  • EurekaMoment
    EurekaMoment Registered Users, Users Awaiting Email Confirmation Posts: 5 ✭✭
    So in other words, if I where install or have installed a 240v center tap transformer between the meter socket and my mains breaker, the meter would record actual power usage and load imbalance would be resolved.
  • EurekaMoment
    EurekaMoment Registered Users, Users Awaiting Email Confirmation Posts: 5 ✭✭
    Oops, The transformer would be rated tor the same amperage as the meter socket/main panel (ex: 100A).
    The revolving stupidity of this is that if National Electrical Code would require the transformer {a $40-60 part, retail}, the power company could use a  240v transformer that would likely cost less on the utility's side to produce, maintain and install.
    - Don't you just love Big-Power ~?~ -
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    edited May 2021 #14
    EurekaMoment, welcome to the forum.

    What is your question here? Yes, you are correct, you can install a transformer on the 240 VAC L1&L2 utility terminals, and have the transformer output with L1/N/L2 and let the transformer "manage" the unbalanced loads...

    HOWEVER, that does have issues. 1) a second transformer creates more losses. 2) the "small" transformer you install at your home is probably much smaller than the pole transformer (which can supply 3-5+ homes vs the "one home" transformer you have). So, unbalanced loads would not be a problem for the pole transformer, but a bigger issue for your small transformer (which would make "unbalanced" L1 & L2 loads more of an issue.

    Utility meters are designed to measure the power--Whether balanced or unbalanced. At this time, most residential power meters do measure kWatt*Hours (real power).

    For commercial installations, they may pay penalties for poor Power Factor--And the meters can report KVAr which is "apparent power"--Basically if you have a lot of AC induction motors (say a large oil refinery or water pumping), the utilty can charge you for the poor power factor (Power=Voltage*Current*Power-Factor). For induction motors, you can install "motor run" capacitors to "fix" the poor power factor of induction motors.

    The whole issue of "AC Math" is actually quite complex... And "simple" fixes (like a second transformer to "balance" poor AC line balance on 120/240 VAC split phase service) or adding capacitors to induction motors can create other issues.

    If you are curious--Looking up specifications for various devices out there can give you a nice view of the underlying details... Just for an idea--Here is a manual for an Electronic based AC utility power meter:

    https://fccid.io/ANATEL/01602-11-07034/Manual/01ED17F8-15A9-412A-A66F-13DC9FC642DD/PDF

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EurekaMoment
    EurekaMoment Registered Users, Users Awaiting Email Confirmation Posts: 5 ✭✭
    Hi, Bill, nice to meet you  and thank you for the kind welcome.
    My post(s) is/are based on Ravs' post stating that utility meters monitor both legs combined, in the case of unbalanced loads the sensor would see power demand and not take into account the power fed back to the line transformer to compensate for the imbalance.
    My introduction of the center tap transformer is to act as a buffer to prevent back-feeding to the line transformer and result in the meter recording only actual power drawn from the grid with no back feeding.
    This is less a question than a postulate that if a center tapped transformer sized to match rating of the meter-socket/mains breaker panel would result in the meter reading only demand-side power usage without to the line-transformer/grid.
    This is not argumentative: I would hope the transformer would be smaller, most line transformers have to do a step down from 20Kv or more depending on the local utility grid layout and the one just outside my back gate is on par with a 35 gallon drum and has a tendency to kill off squeals far more often than I would like (the last one happened while I was working in my yard and sounded like a stick of TNT went off and required my local utility to cut a new fetus in order to restore power - a transformer sized to match the maximum rating of the meter socket and mains panel would be logical as overseeing it would result in flux-based-loss = it has been my experience that unless someone does something extraordinary stupid most residential users rarely ever exceed 30~40% of he rated capacity of their mains breaker.
    3 phase is a completely different situation and is not reliant to split phase residential usage outside of apartment complexes depending on local utilities and codes.
    In my situation, I have 3 meters = 3 micro grids, hence accurate billing for actual power used is important to me, as well as alternative energy sources power management.
    Thank you for your post, if anything I stated is inaccurate or ambiguous, please let me know and correct me on any errors on my part/; I am doing my beset to grasp this material appropriately and from an informed stand point and would like to share my learning with others to prevent repetition of any errors on my part.

  • EurekaMoment
    EurekaMoment Registered Users, Users Awaiting Email Confirmation Posts: 5 ✭✭
    I should have named the account "Oops", sorry Bob, are you an Electrician or an Electrical Engineer, I could realty use input form a EE, well and a physicists - The research I am involved in involves novel design and application where inducers and transformers are concerned largely revolving around a fluid-dynamic model where magnetic flux is concerned (and God help me Spintronics is involved too).
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Transformers (at least the "good ones") are not cheap... Here is a 4 kWatt autowound transformer for $415 (one off/retail):

    https://www.solar-electric.com/x-240.html

    Copper windings and labor cost money (as well as shipping, stocking, and taxes). A 100 Amp @ 240 VAC is 24 kW/KVA...

    The use of an output transformer to "balance" loads from a Split phase 120/240 VAC inverter has been done (allow full power from inverter with unbalanced or single 120 VAC loads). But you can end up with circulating currents and other issues (big power issues).

    I agree that most people use only a fraction of their available panel/utility power--But out here in SF Bay Area, there are a bunch of people installing charging stations for their electric cars. Very quickly--Enough eCars can easily overtax the existing grid and generation capacity.

    Utility meters (at least as I understand) are able to do the math to properly log buying power from the grid and feeding power back--And in day to day operation with a Grid Tied inverter, there will be lots of times when there are "unbalanced loads" where the L1/L2 leads are in "mixed" mode--some AC load, some feeding AC energy back into the grid.

    I replaced the 60 year old electrical panel on my home with larger unit--I did not really draw any more energy--But the utility wanted their engineers to review our local power transformer/distribution system to ensure that we did not "oversubscribe" our local capacity.

    And interestingly, all these folks that are installing Grid Tied solar are actually a "worst case" issue vs the loads (at least at this time--eCars are going to be another issue)--More or less, we use power 24 hours per day (loads), but GT solar generates power about 4-6 hours per day--That means if we balance power generated (Solar) with loads--That the solar array is ~4-6x larger than the loads--So a neighborhood with lots of GT solar can "oversubscribe" local power distribution pretty easily (utility needs to build out more infrastructure, or prohibit more solar installs)...

    3 phase is not that "different" from split phase--There are issues with unbalanced phases, network stability between Delta and Wye based transformers, etc. 3 phase is really cool because it is a naturally rotating field--3 phase induction motors do not need a "starting circuit" to get spinning, 3 phase power is "constant energy" through the cycle (vs single phase power which is 120 Hz of "power pulses"), etc...

    If you need to accurately monitor/log multiple micro grids... I would guess that the utility grade meters today are accurate enough for most needs. (accuracy of 2% or better--If I recall correctly).

    I am not smart enough to help with Spintronics and such. Not sure how you mix electron spin (today being used for make high density computer memory?) vs mains power...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,731 ✭✭✭✭✭✭
    Adding in to this ! For offgrid it is really the electrician/installer's job to balance the loads in a panel. This is super important for split and three phase to keep from generating faults from the battery based inverter power system. Much more efficient and cheaper than doing this with another transfromer, as Bill said.

    Many stack an extra inverter that really is not needed if the panel loads were balanced or shifted from 120vac loads to 240. Same thing in 3 phase.

    Why would you care about this with three meters? The appartment renters are paying for it all,  right?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

  • EurekaMoment
    EurekaMoment Registered Users, Users Awaiting Email Confirmation Posts: 5 ✭✭
    The power grid was never designed to handle distributed power generation so the utility has to treat it a variance in load and wind and solar are unpredictably variable and also part of why “sizing” your system is rammed down your throat so that you feed the grid with as little power as which is the only way a system will actually pay for itself and have a measurable impact on carbon emissions.  The utility will even block you from using storage systems and to provide a known stable constant base load to the grid and if you thought they don’t like wind and solar the absolutely hate micro-hidro because it is a base load provider that they don’t control.

    That’s where the catch/headache is in a multi tenant environment balancing goes completely out the window any time a tenant changes, people move things around and plug different things into different receptacles on the fly, unless everything is running on 240v (won’t ever happen).

    One work around I still haven’t taken off the table is the possibility of separate 240v and 120v power busses; I’ve even considered the possibility of a separate low voltage (12v likely) buss for hardwired lighting fixtures, smoke/fire alarms, etc.  Naturally those would involve transformers again but load balancing would no longer be an issue.

    The HVAC systems are the only place I have 240v loads and even those have an unbalanced load associated with them as the compressors are 240v and air handlers use 120v motors and when I looked into the idea of 240v refit motor refit or air handler replacement the reaction to my enquiries was like I suddenly stated Martian and that I was nuts to be concerned about balanced loads.  And on that same subject: Have you ever tried to find a 240v sump ejector? I have, haven’t found one yet and any time I enquire I’m suddenly speaking Martian again.

    Other real concerns are safety and security and all over the internet and home improvement shows, everything is slapped on a wall in most cases batteries on open racks, no safety guards nothing.  So I thought “server rack”, that’s the way audio and video production companies do it to set up a pure micro grid for their equipment “that’s the ticket” everything neatly tucked away with controlled ventilation and thermal management and monitoring all in one neat clean safe package and the rack can be movable for easy servicing front and back and could even be fully disconnect-able for added safety during servicing; BRICK WALL – from everything I have been able to find out so far not one single manufacture makes a rack mount grid-tie inverter.

    I'm beginning think I may have subconsciously chosen the name I did out a sense of irony because these days if you say “Eureka!” someone dumps a bucket of ice water over your head.


  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    The reason utilities hate consumer power generation is that they have to pay $0.20 to $0.40 per kWH (in California) for power that they pay on the order of $0.05 per kWH--That is dispatchable and under their management (i.e., can supply power at night, when needed in summer for A/C systems, etc.). Why should they pay me to supply variable power at $0.20 to $0.40 per kWH (summer peak) that only makes the grid less stable and does not pay for standby generation/local and long distance power power lines, etc.)... Over the 15 years that I have had GT Solar, California is slowly but surely making GT Solar less and less favorable to the GT system owner... And I understand why (and I saved money/got subsidies when the sun shined).

    The reason that they hate consumer storage--They are concerned that folks will buy power off peak, and sell it back on peak and make money on the spread. For "normal" battery/inverter/charger systems--I believe that the average consumer can, at best, break even when all costs (hardware, battery cycling/replacement, etc.) is taken into account. And since utilities were dragged kicking and screaming to the "retail" consumer power market--The "reason" for "consumer GT Generation" was for reducing carbon emissions and consumer storage (as the utilities reasoned) did not reduce carbon emissions but just "gamed" the retail power pricing plan.

    When consumer GT generation was less than 5% of grid capacity--It was something that could be ignored (and the subsidies from the "poor" that did not own homes/GT solar to the "rich" that did was nicely green washed--5% max was in the original California green energy plans). When the "unmanaged" GT generation market exceed 10%, then it became both an engineering management nightmare  and a financial sinkhole. Neither which could be ignored.

    The utilities did not like wind because it is highly variable while AC loads are not (when I was a kid, the utilities fed variable voltage and frequency to the grid during storms/generation issues--And ended up frying a bunch of refrigerator compressors. AC loads are just not designed for variable electrical delivery.

    Also, even when, for example, wind generation was "nominally" under utility control--At least a few wind sites ignored/refused the orders to shut down during high wind events--Even when power distribution lines were in danger of being overloaded by the excessive wind generation. And wind being highly variable requires almost 100% backup of spinning standby utility generators (nuclear, coal, etc.) to keep the grid voltage/frequency stable.

    Could our AC loads be altered to accept variable energy delivery--Sure. One way that is being used today is to vary the line frequency. 60 Hz=100% grid availability. 60 Hz +/- 1 Hz (i.e., 59 and 61 Hz), the grid has zero availability for GT consumer generation, and could force Electric Water Heaters, A/C systems, etc. to shut down (or go into "low power/grid save" mode). Of course there is a lot of work (in the background) needed to buy new appliances/retrofit frequency controls, slice and dice the "grid" into smaller service areas, etc...

    Your questions/planning on using 12/120/240 VAC systems... Sure, whatever works best for your needs. Each has its advantages and disadvantages. 12 VDC appliances are available, low voltage is pretty safe. But sending "significant" 12 VDC any distance requires short/large AWG copper cables--And at higher current levels, switches/fuses/breakers rated for DC power. Sending 10 amps of 12 volt any more than a dozen feet or so gets expensive to keep a 0.5 volt or less drop (10a*12v=120watts)

    I can plug in a cheap(ish) 12 AWG extension cord and send 10 amps @ 120 volts with 4 volt drop anytime I need (1,200 Watts).

    A quick surge shows 240 VAC ejector pumps (no idea if price is reasonable or not)--Of course these are typical 1 HP or larger--No 1/3rd HP pumps that I could find with a quick search:

    https://www.powerequipmentdirect.com/pumps/240-volt-sewage-pumps.html
    https://www.grainger.com/category/pumps/sump-sewage-utility-pumps/sewage-effluent-pumps/sewage-pumps-systems-basins/sewage-ejector-pumps?attrs=Nominal+Voltage|220V+AC&filters=attrs

    I am sure that if I were in Europe where 230 VAC @ 50 Hz was the norm--Would find 1/3 HP 230 VAC pumps available.

    The issue (I see) with off grid audio/racked computer systems/etc. is that they all demand a relatilvey large amount of power/energy... While there are rack mounted inverters today (UPS systems) and inverters can be made relatively small these days (usually need good airflow for cooling)--The battery storage to supply kilowatts of power for hours one end--Just need a large battery bank and large solar array to keep it fed.

    Off grid solar has always been relatively expensive... I suggest that folks assume they will be paying $1-$2 per kWH (or 5-10x typical utility power rates)--And much of that are sunk costs right at the beginning (building out the initial solar systems)--And replacing battery banks (every 3-8 years for lower cost batteries) and replacing inverters/chargers every 10+ years.

    It is not that off grid solar/hydro/etc. cannot be done--But is it "worth it" for the typical renter/owner consumer. Usually, it is much cheaper to do extensive energy conservation (buying efficient appliances, changing from a 300 Watt desktop computer to a 10 Watt laptop, etc.). And if you need (for example) a rack mount computer system... Rent a rack in a data center with cheap power (like in the northwest with lots of hydro) and remotely manage the system.

    There are some "green energy" data center plays that are being done today... For example, many modern electronic gear rated for 100-240 VAC use can take ~380 VDC power... Run a 380 VDC battery bank (and support equipment) and save the losses/expenses of converting from 48 VDC to 120/240 VAC back to low voltage DC to run the computer:

    https://datacenters.lbl.gov/sites/default/files/380VdcArchitecturesfortheModernDataCenter.pdf

    Does this make sense for large data centers--Possibly.

    Does this make sense for "home/offgrid commercial"--Probably not--You do not want to be around a 380 VDC battery bank during a short circuit event:

    https://www.creativesafetysupply.com/articles/arc-flash/
    Video from link:
    https://www.youtube.com/watch?v=2SopsQEfoc4

    Locked access, training, protective gear, etc... Not cheap.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset