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Explanation of how kilowatt-hour meters work (electromechanical)
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- เผยแพร่เมื่อ 2 ส.ค. 2024
- I take apart an electromechanical power meter and describe how it uses magnetic fields to measure power consumed.
The voltage coil's numerous turns of wire already provide some phase shift -- the copper ring adds additional shift to bring the total up to 90 degrees.
As an electrical engineer I always wondered how centipedes worked, this helped a lot!
Take a look
th-cam.com/video/ImAiF99GuIQ/w-d-xo.html
Whaaaaat?
@Romanes eunt domus That comes later. Probably over a hundred million years later.
@@guilhermetuche deleted :(
peristaltic wave movement
The stippling on the disk is called "planishing", and is a manufacturing thing, to get the disk real flat. If you pressed a bent disk between flat dies, it would spring back and retain some of its warp. The stippling permits plastic deformation of the disk, even if initially flat. You will see this on telephone relays and other stamped assemblies for the same reason.
Meter will read correctly only it is mounted upright; the bearings are not designed to bear side-load.
Shaded pole motor: the shading coils are needed continuously. The reason is that these small motors have a "goodness factor" less then 1. Such motors will not self-rotate even if initially spun up. In shaded pole, it is not practical to get phase shift over 45 degrees. (You can, but amplitude of magnetic field left is minuscule.) That's why there is double bar in motor. It is a shaded, shaded pole. Analysis is like RC circuit. Look at phase shift versus R. Raising R increases phase shift at expense of voltage on cap. In meter, it is practical to get near 90 degrees, because you have absurdly large voltage coil, and only the tiniest "motor" output. Meter motor is running at high "slip", so torque is independent of rotor speed, even at the highest load.
This is an old meter, being only good for 15 amps. But ones I have are older, being only good for 15A at 120V. Mine are from a power panel in an old building in Akron Ohio slated for demolition.
Thank you for this! Planishing sounds like a great way to make that disk for very little cost and time, but still have a high quality result.
Is the 'shaded, shaded pole" the reason for the asymmetric lower coil then?
Brian Park
God info, Thanks
So does the voltage coil change the rotation speed if a constant current draw is present and the voltage changes like say a brown out where voltage drops from 220 to 150 or so? Reason I ask is I have been wondering if my daughter is getting over billed because they only have 110 coming in to the ancient house she is renting instead of 220...
@M Detlef DIE noun. a block of metal used for pressing or cutting something into a shape or pattern -Macmillan dictionary
0:05 Please observe in the lower right of the line just below the word "FOCUS" and there you find the designation Kh 7.2 It is the meter's golden number... (for calibration)
In 1974 I needed to measure the power consumption of an industrial process. I needed to measure WATTS of power. In those days such a meter would cost us a few thousand dollars. Instead, I spoke to the "engineer" of the engineers at the power company, and he recommended I use the "power consumption meter" like we all have on the outside of our buildings. These were said to be accurate to within a 1/4 of a percent down to one tenth of percent of the full scale power handling of that meter. If the power company was happy to trust it's charges to it's customers for thousands of dollars, so would I trust it's accuracy. I bought a certified and calibrated one for $125.00 from their supplier. And pretty simple to use. (Also quite useful for power consumption diagnosis at home). HERE'S THE SCOOP..... That "Kh number" for the meter tells "how fast it is" you'll see 7.2 or 14.4 or 28.8 on different meters. Any way, time the rotation of the spinning disk in seconds, and use this formula "" The Kh number times 3600 divided by the number of seconds for one rotation of the horizontally spinning disk EQUALS the WATTS through the meter over that same time period "" Damn that's so easy!!! want to find out the consumption of an air conditioner, refrigerator, a heater, electric range, a furnace? Just turn off all devices but that one, time one rotation of the spinning disk in seconds, and you've done it!
Here's a few examples:
Kh 7.2 times 3600 divided by 17 seconds for one rotation is 1524 WATTS for a heater.
Kh 14.4 times 3600 divided by 81 seconds for a rotation is 640 Watts for a refrigerator.
or Kh 14.4 times 3600 divided by 8.1 seconds for a tenth of a rotation is 640 watts for the same refrigerator, didn't want to wait for the full 81 seconds. You can use your head. And couldn't be sure the frig compressor was ON THE FULL 81 seconds.
How about the cost of all the Christmas lights you're running on the front of the house?
Of course a Kilo-watt-hour meter costs $40 has a lot more features and is easy to use, but back in those days, this accomplishment was impressive and useful. Boss was impressed too.
If you like this comment, I'd love to hear comments back, just below here. Thanks
Awesome
@@junkmail4613 In English the words ITS and IT'S are spelled differently because they mean different things.
MrCuddlyable3 17 minutes ago, "@Junk Mail In English the words ITS and IT'S are spelled differently because they mean different things."
According to "www.merriam-webster.com/dictionary/it's"
"
This apostrophe form of the possessive remained extremely common throughout the 17th century and was used by the likes of Thomas Jefferson and Jane Austen. The version without the apostrophe only became dominant in the 18th century-probably because it's was taking on a new role, replacing the contraction 'tis.
It would be simpler, of course, if there were only one form in use, and there's an argument to be made for using it's in all cases; 's serves both purposes just fine for nouns. In the cat's bowl it signals possession, and in the cat's sleeping it represents the contracted verb is.
"
According to me:
Making this distinction for the sake of "The current FASHIONABLE" usage IS REPREHENSIBLE and makes the language more "self-contradictory" Apostrophe s added to any noun is used to indicate possession, OR used to indicate the missing "i" in the contraction for "IS", so adding "'s" to the pronoun "it" is CONSISTENT with making it possessive in the context of the word, and so IT'S CONSISTENT in IT'S USE, and I WILL use it in OUTRAGEOUS PROTEST. Go prick yourself!
Making room in the language for the replacement of " 'tis "certainly is rather obscure in this day and age. Let the language be smooth and streamlined and NOT HAVE A LOT OF IDIOMATIC EXCEPTIONS. " 'Tis much better left to itself"
So it's like 7.2 Joules-hour per rotation (or 14.4, 28.8, etc.), good to know. The "Kh" probably comes from the dimensional analysis coming down from kilowatts-hour (kW.h) and kilohertz (kHz) of the disk.
The 7.2, 14.4 and 28.8 reminded me of 2 things, digital audio kHz and the kbps(kilobits per second) of old dial up modems. It all has to do with the frequency of information in its format, in these two is a signal, but in the meter it comes down from how many turns it takes to get your kW.h
Pretty good explanation of an older watt-hour meter. I was Quality Engineering Manager for Sangamo Weston's watthour meter manufacturing business in the 1980's. The stippling on the aluminum disk is mainly to maintain flatness. There were only 4 manufacturers of these type meters in the 1980's. The electronics revolution created 100's! We sold 1 million of these single phase meters per year.
Would you happen to know what the expected 'lifetime' is of those Sangamo watthour meters? How do they degrade over time and what the usual failure modes? I have heard people having them for 30+ years, even as they were later updated with electronic ERT broadcasting gizmos to make it easier to get the usage info, and reclassified as 'electromechanical hybrids'. Does anyone in North America still manufacture new(not refurbished) electromechanical meters?
@@kengartner204 I don't know what the expected lifetime is now, but each utility company has their own standards for replacement, with some validity due to differing climates.
Failure modes used to be mostly from people thumping them every time they passed by... that's not gonna make them speed up! Many modes of tampering too. As far as Mfg. Defects, if they are properly calibrated before installation, very little can go wrong with them.
The Big Four meter makers were GE, Sangamo (now ITRON), Duncan, Westinghouse. Don't know about now.
When you mentioned the copper on the volt coil, I immediately thought of shaded pole motors, then along came a shaded pole motor! I work in the electricity transmission business and the principle of the moving disk, is used extensively in old protection relays, some giving delays before tripping a circuit and some with selectable tripping characteristics. All very clever stuff and still used in many places around the world.
They are also used in both old & new AC (for the drive coil) relays. In this case, the shaded pole creates a delay not in seconds, but in about an eighth of a line cycle. The magnetic circuit is split, one half being delayed, the other not. This way, there is always a non-zero magnetic attraction at all times (because the zero crossings misalign in the 2 paths) to hold the armature in against the return spring & prevent buzzing.
I found this extremely informative and very well made, you seem to have anticipated every possible question somebody would have while watching this, you spoke clearly and gave clear shots and explanations of what you were showing. I almost never comment but I genuinely feel like you deserve the acknowledgement. Thankyou!
what a beautifully design instrument. you can tell somebody took pride in his work there.
Funny you say that. Was made by Nikola tesla, then tampered with by electric company's engineers
These mechanical meters are so reliable, the one hanging on the side of your house may be 50-70 years old. But that's a long time for a mechanical device, so many of those old meters developed "stiction" and just didn't register with lower currents. As a result, those customers were ridiculously under-charged. When the customer got one of the new electronic meters, they were now being charge fairly, which meant their bill jumped! Hence: lawsuits.
Some early electronic meters used Rogowski coil current sensors, which have problems with fast switching, non-linear loads (for example LEDs) causing them to overreport quite significantly.
This is why power meters are not owned by the customers and are getting exchanged every few years. How come a customer changes from an old mechanical meter that has stiction already to a new electronical meter?
Kullat Nunu It doesn’t make any sense for the client to own the meter. Everyone would just have a faulty meter and save millions. Why do you even bring it up?
@@askhowiknow5527 That's actually what I ment. Didn't Jeff Kurtock write: _so many of those old meters developed "stiction" and just didn't register with lower currents. As a result, those customers were ridiculously under-charged. When the customer got one of the new electronic meters, they were now being charge fairly, which meant their bill jumped! Hence: lawsuits._ that's why. I wanted to know how a situation like he described could occur at all.
@@xaytana _Nobody here has stated that a customer had bought a new meter themselves_ , nor did I. Where did I state that? And yes, It doesn't matter if a new meter was bought or received when it comes to technical properties of those meters. That's why I wrote _This is why power meters are not owned by the customers and are getting exchanged every few years._ What matters and that is what Jeff Kurtock wrote, is the fact that a customer having an old meter that developed "stiction" already which _ridiculously under-charged_ , gets a new meter that now allows a fair (higher) charge. But this would necessarily imply that mechanical meters develop "stiction" within the exchange interval, doesn't it? My question therefore was, how can it be that a meter develops "stiction" within the exchange interval which certainly is not 50-70 years. He wrote ... _50-70 years old. But that's a long time for a mechanical device .... As a result ..._ . Jeff Kurtock just didn't explicitly mention an exchange interval nor a typical timeframe for mechanical meters to develop "stiction" within that exchange interval. Therefore my question.
Thank you for this! I have a 1931 Westinghouse OB version wattmeter that I've been intending to make a keepsake lamp out of for about 25 years and I was having trouble remembering how to wire it. This video got me on target. Cant wait to complete the project!
I remember watching the one on my house when I was young. Mesmerizing.
@ebulating lmao
When I asked my dad one day about the seals on these, he told me they were there because otherwise people could pull the meter, turn it upside down, and run it backwards. Now, my dad was a quite well known EE and I'm sure he didn't use those actual words, but he did get his points across about honesty. Take note, I was 14 at the time and my father was not /necessarily/ attempting to speak accurately to me about how meters work.
Things our children will never see. Sad
Yep. Mesmorized by racking up the bucks!
The aluminum disk had a black area on the edge, we called it the "choo-choo-train" and would wait to see it come around. Some times the train moved slow and some times it was really fast.
I'm a bit disappointed that you didn't remove the magnets to show it spinning really fast
I've always wondered how these meters work. Thanks for the excellent explanation.
me also. Very cool video. :)
Excellent presentation. I want to just add: The phase of the inductor is not perfect (as your added note on the left stated) because the coil also has resistance. The resistance of the coil adds an in-phase component to the current, shifting it away from a perfect 90 degrees. So the added corrective inductor is used to calibrate it to 90 degrees.
I like the centipede analogy.
I literally was wondering the other day exactly how these work. Thank you. This video is very informative.
what a thing of beauty! you can tell somebody was really taking pride in his work, and wanted it to be pleasung to look at, over just functional.
Fantastic! Oh how I love the clever ways the pre-digital world devised all manner of measurement, timing and industrial control. I find it amazing just how far the electro-mechanical world developed. Until the 80's, the highest tech digital around our house was a wristwatch and a 4-banger calc!
The inside of an electro-mechanical SLR film camera is also very interesting with various controls for aperture, shutter speed, ISO, light metering, timers etc..
I love your channel! Clear, concise explanations. I'll dig into more of your videos and wait with anticipation for new productions!
So well presented and excellently filmed, thank you for posting .
Thank you for this video! I always wondered how these things worked, and you explained it perfectly. Even though i may not understand the complete science in it all, the way you explained it made it easy to understand.
Yes, there are multiple magnetic fields from both the coils and the generated eddy currents (in the alu-disc near the coils). The offset between these magnetic fields creates the motion (like two magnets can move each other from distance because of their magnetic fields). Quite fantastic in my opinion :)
As an electrical engineer, I worked on the manufacture of a specialized piece of test equipment to trick these meters. It combined passing full voltage combined with high current from two separate sources. The meter was thinking it was reading 30KW, when in fact the equipment was only drawing less than 1.7 KW. We used it in the calibration of wireless meter reading designs.
Incredible.......all these years as an electrical engineer in industrial power and we never learned about this......true Faraday genius IMHO.
Not to be a dick or anything, but that kind of makes me go 'yelp!' about the level of electrical engineers in industrial power... Surely you knew about the whole induction causing eddy currents in the aluminium disc to spin it up (and people using neodymium magnets to slow them down)?
@@freakyjason477 - certainly did know that which you point out!!!!...the courses focus on the most critical knowledge to become a proper BScEE within a 4.5 year time frame....
one's failure to comprehend the width and depth of all there is to know about electrical engineering is very telling indeed!
I've wondered how this thing works since my childhood and this video made it all very clear. Thanks and keep up the good work!
At the start you show the analog meter and digital meter inline with the load. Did you run them long enough to see how close their measurements are? Great video and explanation.
Guess we will never know….
I doubt they would show the same, especially since the analog meter is only made for vertical mounting, not lying on a bench, and the digital meter is probably not very accurate either, considering it's a plug-in-socket type of solution.
I always wondered what those copper rings were for in shaded pole motors.
Awesome stuff mate. You are a wealth of knowledge!
Thanks for this vid, Ben. My father is an electrician and he brought one of these home for me to take apart when I was about 12 years old. I was amazed by the magnet/needle bearing and I've never seen one since. I made something to hold the disk so I could spin it and watch it free-wheel for a very long time, but then be amazed that the permanent magnet would stop it in less than a second. I didn't understand why that worked until i was much older. Make another video on a further teardown.
This is a very good description of a lot of it. Thank you!
As an electric engineer i liked that centipede analogy. Good video.
I felt like I was staring slack-jawed as much of the information flew over my head, but I was rapt the entire time. Thank you, Ben Krasnow!
Thank You very much. I was struggling with the energy meter's construction but couldn't find enough resources. Keep doing great work like this.❤❤❤
ouch! my head hurts. great job man. you do really great at breaking things down!! this one is just complicated.
I like this explanation. It's the first explanation I've seen and actually fully understood. (And I've wondered how these damn things work for the longest time.)
Also, Douglas Adams reference at 6:40.
My father worked for the electric company for many years and had quite a few of these around so we can make desk laps with them. Thank you for an interesting video!
The voltage coil's numerous turns of wire already provide some phase shift -- the copper ring adds additional shift to bring the total up to 90 degrees.
Thanks sir for your beautiful video
I ll use it to learn how to explain it in my classroom.
I admire how you can explain it so clear and simple because it's a complicated phenomena.
the rotating disk is alluminium i guess and those copper rings provide just ennough phase shift to make the total phase shift exactly the desired offset.
Thank you very much! Always wanted to know at least just a little bit of how kilowatt-hour meters works. That was great!
Man, I follow about half of what you're saying, and often times even then in vague terms, but I love watching your videos and your explanations.
Very good video. I've wondered many times when I go past my meter what goes on inside the glass. Thank you!
You're an excellent communicator and taught me something new with this video, thanks! I did however get a little nervous where you didn't plainly show that you unplugged that thing before ripping into it! Wow!
thank you so much for shaded pole motor explanation. I always wondered how copper rings work as starters
I'm here because my old meter has added a whopping 42000 kWh (42 MWh) in six months when it should have registered just 7 to 8 MWh. As far as I can calculate that's almost physically impossible without tripping a breaker somewhere [often], which hasn't happened once. The meter now appears to be registering normal usage again, making things even more mysterious.
It's six months because that's how often they read the meter here and I now have the bill. Over $9000 (Australian dollars).
It's an old single phase 240V 60A meter and the main isolating breaker is 63A. Household draw peaks at about 25A, so that leaves only 38A max for any background leakage current that might have existed.
Simple calculation tells me that it would take a minimum of 160 days to leak the amount of energy over what I've used without tripping the main breaker.
The biggest breaker in the house itself is 32A, which if the leak is in a house circuit would set the minimum period at 190 days.
Even then it would require a perfectly steady leak at just under the respective breaker values for the entire period, which I know is impossible.
So I'm looking at a very strange and unlikely meter malfunction or human intervention.
Luckily I actually monitor and record my HVAC system, which is by far my biggest user of power. It matches the previous year's usage closely.
Hi Ben, interesting channel, one of the best teardown and electricity stuff channels in youtube. thank you.
The potential coil is an inductor, and as such, current naturally lags voltage, but with the open pole piece, it is not in a complete magnetic frame, so it needs the coil pole piece to complete the phase shift to 90 degrees. The current coil has little iron and few turns so it's inductance has very little back EMF limiting current and shifting power factor. They produce fields in phase with the current drawn.
No clue on the offset current coil other than possibly to compensate for the mechanical drag as it is not friction-less. This may have been produced to make the meter more linear in accuracy at all load currents. This may be a guess on my part.
Sorry, I should have mentioned the voltage coil is wired across the line, so its magnetic field is proportional only to the voltage of the circuit. The current coil is wired in-line with the load, so its field is proportional only to the current.
That makes sense. I've always wondered about it. Thanks for posting!
Mathematical reason for the phase shift:
d/dx(sinx)=cosx
Cosine is the instantaneous change (derivative) of the current, so the magnetic field is max when the derivative is greatest.
The 2 different current coils in the bottom of that meter are most likely a design by GE. All modern electro-mechanical meters 1970 up have 2 indeferent coils on the bottom. If a kWh meter is rated for 1 phase it will have more windings than one coil, if it is rated for split single phase it will have 2 exact coils with 2 phase in the voltage coil.
Great stuff, another mystery solved, cheers.
Indeed he is a great teacher, but there's plenty of other source around for broad topics what i love about this channel is the randomness of topics and the caring love Ben put on sharing them.
I believe the dimpling on the disk is primarily for rigidity. A sheet of 16 gauge steel is very flimsy, but when it is given ridges it can hold much more weight (for example a truck bed) without flexing or bending, that's why the floor of a car and a truck bed have those shapes stamped into them.
Yep and one knock and the slightest deflection and it won't slide through those magnets. They would be unable to charge for any electricity. They probably did that as reaction after a few homes went uncharged. Plus it stops people from tampering with it. If the dimpled disk were bent out of shape someone would know you did something. Smart customers of the late 1800s would be smart enough to go into their device. Bend it slightly and just say it was ware.
jefrhi That's some serious bullshit lol. Retroactively making you pay for something when they have NO idea how much you used? That doesn't even sound legal.
Not to mention Electric companies make a fortune off consumers... say even just $100 a month off a person and they power a million people... I don't believe for a second it costs a hundred million to power that plant, so their profit margins are definitely large enough to let THEIR mistake slide.
its not just the plant but also infrastructure replacement, power line maintenance, sub stations, etc, etc. Oh and lining the pockets of CEO's but that's an entire other issue.
@Phoenix See 12:32. The disc connects to the gear that train makes the different dials spin at the correct ratios. The electric company can then read how much electricity was used.
And this was already designed 100 years ago?? Sometimes I really do believe that the amount of intellect on this planet is a constant value..
Love the centipede analogy!
Thanks. I've wondered about this myself. There are actually two copper rings (one above the disc and one below), and the lower one has additional lobes and shapes that I do not fully understand. The adjustment of the permanent magnet can probably be setup to work with whatever torque they get from the coil design, so the whole thing can be fairly easily calibrated.
I freaking love this channel!
You truly fight mass stultification, thank you very much! Also, really nice video!
Good stuff Ben!!! Thanks for posting!
It's a good question. I believe the system would work with just one current coil, but it's easier to manufacturer the single iron pole piece to be symmetric and balance the magnetic field between two areas. There is also magnetic shunting in the pole piece, which may be easier in a symmetric design.
Sir, you’re very good at explaining. Thank you.
Wonderful, very enjoyable listening to you share your knowledge!
Best explanation I've ever seen !!!
Nice explanation, reading about it is one thing, this puts it all together. Cheers, Mark
It's really something when I have a question, go to search it, and then the answer was just _there_ all this time in my subscriptions.
Thanks for the shaded pole explanation!
Great video. The marks on the disc make it easier to calibrate a batch of meters. Single Phase meters are usually tested in batches of 20 or 30 or more. At a 10 revolution test it is easy to determine the overshoot or undershoot direct in procents. Black mark at front, Current and Voltage applied, 10 turns of the disc and stop. Current and Voltage off. adjust and repeat to get the meters within the ± 2 % or better.
The Watthour Meter By William Martin Shepard, Allen G. Jones, 1910 on Google Books is an excellent source for more information on the Watthour meter. I believe it has an explanation for using dual copper rings to achieve the 90 degree phase shift.
In the squirrel cage motor (shaded pole), the copper wire is disposed in diagonal in the inside part, close to the rotor (the cage). This help to decide the direction the motor start. This was important for turn table and still is for fans so that air is pushed in the same direction.
Ah, an unexpected Ben Krasnow video! And a very good and informative one at that.
Ben is a really cool guy and an inspiration to all of us.
I was looking for this, thanks!
Amazing! where other place could we find an information like that?
Thanks you for sharing!
The neutral actually isn't metered and doesn't connect to the meter. Notice it's a "240 volt, three wire" meter. 240 volts is self explanatory, but the third wire referenced is the neutral. Each of the two lines ("hots") are metered by each set of coils. If current is only flowing on one line (ie a 120 volt load), the meter revolves half as fast as it would if the same current were on both lines (either two 120 volt loads or a 240 volt load, twice as much power). If it were a 240 volt, two wire meter, it would only have set of current coils, the other line being tied directly to the load.
AFAIK in the US 220/240V lines are made the way so two of the wires are L (hot), but the phase is shifted 180 degrees. And for 110/120V you just use Hot and Neutral wires.
Interesting and informative, I enjoyed your video very much. Thanks.
great! interesting also that the oldest (yet reliae) protection relays for substation protection works on the same principle, mesasuring energy that passes though the wiringa during specific events.
Very well presented. As you went along I was thinking about the shaded pole motor, wondering why it doesn't spin at a little less than 3600 rpm. I wonder how well this system compensates for current imbalance between the two legs, ie neutral wire current....
This is so cool! Thanks for explaining another small chunk of our world.
that only exist because of the money god, a god of our own making
Hi, to answer your question on the split current coils, you have already answered . your own question with tension offset. Essentially you have one coil that is unevenly split either side of the central electro magnet. Thus when powered up, ensuring that the spigot direction is always positive and thrust is controlled with a current offset differential.Hope that helps. Good demo though.
Thank you for sharing your knowledge.😎🤙
Thanks,always wondered if I was been charged for watts or VA. Great video as this explains it.
I don't understand why the copper loop is there. In the current coil the magnetic field is proportional to the current, while in the voltage coil the magnetic field is proportional to the time integral of the voltage. If the current is in phase with the voltage then the magnetic fields are going to 90 degrees out of phase without the copper loop. Maybe the copper loop is there to compensate for the resistance of the voltage coil. If the coil has a high resistance the magnetic field will lag by less than 90 degrees due to the voltage drop across the resistance. In that case it would make more sense to have the copper loop.
Much appreciated this was a great thing to learn :)
Captivating. Thank you for the video.
Very nice video. Learned something today
Very cool as always.
Awesome explanation.
Thank you so much I was always wondering what is this little piece of wire on the engine's stator for.
Thank you very much for this video.
The current coils are wound in the opposite direction because this is a 240V meter designed for a split phase 120/240v system (standard household electrical service). When the voltage coil is connected to 240V a 120v loads only is only flows though half the meter or the meter will register twice the actual KW/H used. You can connect this type of meter to 120v supply; the current coils need to be connected in series.
sep.yimg.com/ty/cdn/yhst-97927213475128/wiringguide-form2s.pdf
sep.yimg.com/ty/cdn/yhst-97927213475128/wiringguide-form2s-240v.pdf
Form-2s, 120/240v meter are around $20 used.
The meter is for an one phase (240V) electrical system (live + live) but with a center tap as a neutral. Meaning, center tap to any end you get 120V... but from live to live you get 240. To measure energy used from live to live AND any live to center tap (N) you need tvo current measurement elements. For better description see google: single phase three wire 120/240
Great video, always like mechanical meters and the US ones always had a tendency to be round vs the UK square ones despite still often.being GE. On the two current coils, meters don't generally care about the neutral, they just need it for the voltage coil. I think it's possible the same movement will do a split phase with 220/110v 3-wire system where the two sets of current coils will measure the two lives (or hots) which are 180deg out of phase due to effectively a center tapped transformer supply. If they didn't connect it in a single phase 2-wire, it would affect accuracy. It being connected to neutral would mean it's being there is cancelled out and the accuracy wouldn't be affected. I think thats why anyway!
the easiest explaining of kWh meters and the best part is structure is very nicely defined by physical properties behind them
This was great! Thanks, Ben. I've always wondered about these.
Now that we have PV, PG&E gave us a digital meter, so I don't have the satisfaction of seeing the wheel spin backwards.
The asymmetric coils are most likely there so that the power being consumed on the 120volt and 240volt lines generate the same amount of force acting on the disk. Its current and the number of windings of the coil that influence the strength of the magnetic field. So one coil must be larger to equally generate the same amount of magnetism as the other. Example: P=VI: 120volts * 1ampere = 120watts, but 240volts * 1ampere = 240watts. Therefore the current is the same but the power is not, so one (240volt) coil must be larger (having more turns) to increase the strength of the magnetic field to equally exert the same amount of force on the disk as the other coil (120volt).
pretty complicated piece of equipment, pretty smart, I wish you showed step by step by applying certain calibrated amount of Power to see the effects in different loops
I remember reading that when the digital meters were introduced they were ridiculously over reporting power consumption. Lawsuits were had.
yea when i had a smart meter installed to work with my solar panels i noticed a huge increase in power usage despite generating electricity from solar.. energy companies are sneaky buggers
Thanks!
Well done. Meter readers often feferred to as "motor readers" in these parts. Thanks for posting!
thanks Ben, I would've never known how that worked
fantastic explanation, thanks
When you pointed out the asymmetrical current winding, I wondered whether this affected the meter's operation when the power flowed in the other direction. A simple experiment would be to hook the meter up the way you did and measure its reading. Then hook it up backwards-load to source terminals and source to load terminals, then measure its reading again. Does the meter measure power at the same calibration coming in as going out?
Yes. Great question. I can provide you with something that you can ponder about. My meter started to run in the opposite direction when it was hooked up to solar "PV" . The meter was measuring identical consumption in both direction.
Testing gets done for Base load, Base load at 0.5 PF and Light load. Then Middle load gets run and errors noted.
e.g. Class 100 meter. Test Amps 15 = Base load.
Adjusting is done at BL, PF and LL
The test bench has a multi-turn potential coil to avoid, the meters reading each others burden.