> The UK Magazine Everyday and Practical Electronics (EPE) did a project
> for this a few years ago using a PIC16C84, the actual sensing was done
> using a hall effect transformer device. I built one, it works really
> well!.
> --
>
> Nigel.
>
>         /--------------------------------------------------------------\
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> > My question is this.  Do I have to measure phase, via current and
> > voltage, in order to get a usable value?  And if I do have to have both,
> > I would prefer to use the CT for current and a galvanic field sense
> > method to 'see' the voltage.  I would not get an accurate absolute
> > voltage, but I would get an accurate phase lead/lag.  And if I have the
> > phase angle and current, how would one then calculate the KVA's?  I once
> > knew some of this stuff from school, but you know, don't use it and you
> > loose it.
>
> In theory, the electric company charges you for the instantaneous voltage
> times current integrated over the billing period.  This is also the measure
> of the amount of energy delivered.  So, if you wanted to perform the same
> measurement, you would have to sample voltage and current "often" compared
> to the 60Hz line frequency, then multiply and filter the result to get live
> power useage, or accumulate the result to get energy used.
>
> However, if you just want a quick idea of where the power is going, you
> probably don't need to be this sophisticated.  Just measuring current will
> probably give you a pretty good idea what is going on.  If the current is
> low, then the power drain on that line has to be low too.  A high current
> could in theory indicate either high power consumption or a large phase
> angle.  If both current and voltage are sinusoids, then the power drain is
> the RMS current times the RMS voltage times the cosine of the phase angle.
> Note that even at a 45 degree phase angle, the power is only 30% less than
> indicated by measuring the current alone.

>
> I know this subject has been thrashed somewhere back in history, but I
> cannot help it.  My electric company (Duquesne Light in Pittsburgh) is
> kicking my ass with the bill.  I am so spitting mad that I could
> co-generate.  $300+ per month when not even in the winter is
> rediculous.  So I have been pondering making some measurements so that I
> can identify where the electrons are all going.  I envision a small PIC
> based device with a current transformer that is put on each feeder in
> the breaker panel.  A simple serial bus to a PC, and voila, I am logging
> use on individual branches.
>
> My question is this.  Do I have to measure phase, via current and
> voltage, in order to get a usable value?  And if I do have to have both,
> I would prefer to use the CT for current and a galvanic field sense
> method to 'see' the voltage.  I would not get an accurate absolute
> voltage, but I would get an accurate phase lead/lag.  And if I have the
> phase angle and current, how would one then calculate the KVA's?  I once
> knew some of this stuff from school, but you know, don't use it and you
> loose it.
>
> Chris Eddy~
>
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>
> > This is also the measure of the amount of energy delivered.
>
> Not really.  THey charge you as if all phases were delivering the same amount of
> power.  If all your energy comes through one phase (because you have thing
> plugged into the breaker box in an unbalanced manner) then you will be billed
> the same as if ALL phases had that much power coming through them.
>
> In other words, you would be giving away LOTS of money.
>
> Andy
>
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> power.  If all your energy comes through one phase (because you have thing
> plugged into the breaker box in an unbalanced manner) then you will be billed
> the same as if ALL phases had that much power coming through them.
>
> In other words, you would be giving away LOTS of money.
>
> Andy
>
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> -----Original Message-----
> From: Roman Black [SMTP:RemoveMEfastvidspam_OUTKILLspamEZY.NET.AU]
> Sent: Tuesday, October 24, 2000 1:07 PM
> To:   RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU
> Subject:      Re: [EE]: best way to measure KWH
>
> Alan B. Pearce wrote:
> >
> > As you are trying to find where the power is being used, I suggest you
> only need to measure current. Within a household the power factor should
> be close enough to 1 for all appliances that the phase difference between
> voltage and current will be minimal.
> >
> > The highest current path is going to be the one drawing the most power
> unless you are running something like a welding transformer without power
> factor correction.
>
>
> Yep, I agree. Plus in a household environment the lights only draw
> maybe 2% of the total current, "wacky" loads like PCs and electronic
> devices maybe 10%, almost always electric heating is the culprit.
> Running too many electrons through a wire until it glows hot is a
> very crappy way to get heat, I think only 15% to 20% efficient
> in most household devices.
>

>
> Serious as can be.
>
> If you know what you are doing, you can harness the difference and put it to
> work.  My brother set up a textile factory wehre he worked so that the
> ventilation fans, a necessary evil, ran off the difference between the phases.
> They cooled the building essentially for free.
>
> The sad part was, the plant electrician didn't understand what was going on and
> went ballistic.  Only after the accountant told him the electric bill went down
> (because the fans had previously been on one phase) did he shut up.
>
> Too mysterious for him, I guess <G>
>
> Andy
>
> "M. Adam Davis" <spamBeGoneadavisSTOPspamEraseMEUBASICS.COM> on 10/24/2000 09:36:28 AM
>
> Please respond to pic microcontroller discussion list <KILLspamPICLISTspamBeGoneMITVMA.MIT.EDU>
>
>  To:      EraseMEPICLISTEraseMEMITVMA.MIT.EDU
>
>  cc:      (bcc: Andrew Kunz/TDI_NOTES)
>
>  Subject: Re: [EE]: best way to measure KWH
>
> Are you serious?  It sounds like what you are saying is the electric meter finds
> the phase with the highest current draw, assumes the other phase is drawing the
> same and bases its measurements on that?
>
> I would be very interested in finding out about this.  The larger of my power
> hungry appliances use both phases, but the fridge uses only one.  Not to mention
> the number of computers that use only one.  The way my place is wired, I
> wouldn't be surprised if the loads were not distributed evenly.
>
> This doesn't make sense...  It shouldn't be too difficult to add the current
> draw from the phases.
>
> -Adam
>
> Andrew Kunz wrote:
> >
> > > This is also the measure of the amount of energy delivered.
> >
> > Not really.  THey charge you as if all phases were delivering the same amount
> of
> > power.  If all your energy comes through one phase (because you have thing
> > plugged into the breaker box in an unbalanced manner) then you will be billed
> > the same as if ALL phases had that much power coming through them.
> >
> > In other words, you would be giving away LOTS of money.
> >
> > Andy
> >
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> > "[PIC]:","[SX]:","[AVR]:" =uP ONLY! "[EE]:","[OT]:" =Other "[BUY]:","[AD]:"
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> > This is also the measure of the amount of energy delivered.
>
>
>Not really.  THey charge you as if all phases were delivering the same
>amount of
>power.  If all your energy comes through one phase (because you have thing
>plugged into the breaker box in an unbalanced manner) then you will be billed
>the same as if ALL phases had that much power coming through them.
>
>In other words, you would be giving away LOTS of money.

> "The electric meter actually simultaneously measures voltage and
> current on each leg, and then adds them up.  This is obviously a
> pretty simplified version of what's happening inside the meter, but
> that's the bottom line for your electric bill.  If your load is
> unbalanced between the two legs, you're not getting charged
> double for the unbalanced portion.
> It's actually a vector multiplier, where the voltage vector is multiplied
> by the current vector, and the product of those two is what pushes
> the wheel around.  But I'm sure that's much more than any normal
> person (I, on the other hand, am an engineer) would want to know.
> The only real problem with leg unbalance is that SRP transformers
> can get warmer if the phases are unbalanced, but that's really
> SRP's problem, and not yours to worry about."
> ------------------------

>
>
>
> The Perfect Image Graphics Co.
> 2429 W. 12th St.
> Tempe, AZ 85281
>
> 800-533-8732
>
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>
> This topic seemed interesting so I emailed one of the local
> electric companies and the following is a response from one of their
> engineers.
> -------------------------- snip ------------------------------------------------------
> "The electric meter actually simultaneously measures voltage and
> current on each leg, and then adds them up.  This is obviously a
> pretty simplified version of what's happening inside the meter, but
> that's the bottom line for your electric bill.  If your load is
> unbalanced between the two legs, you're not getting charged
> double for the unbalanced portion.
> It's actually a vector multiplier, where the voltage vector is multiplied
> by the current vector, and the product of those two is what pushes
> the wheel around.  But I'm sure that's much more than any normal
> person (I, on the other hand, am an engineer) would want to know.
> The only real problem with leg unbalance is that SRP transformers
> can get warmer if the phases are unbalanced, but that's really
> SRP's problem, and not yours to worry about."
> ------------------------ snip ---------------------------------------------------------
>
> The Perfect Image Graphics Co.
> 2429 W. 12th St.
> Tempe, AZ 85281
>
> 800-533-8732
>
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> I think you're only looking at one part of the conversion process though.
> Take the case of e.g. a gas-fired home heating system compared to electric
> heating from generated from a gas-fired power station (chosen to keep the
> comparison fair).
>
> In the latter case you burn the gas to produce heat, convert the resulting
> energy to electricity with a pretty low conversion efficiency, transmit the
> electricity with the attendant losses in several transformers and many miles
> of cable and then use it to heat the house. In the former case you just burn
> the gas to produce heat.
>
> .
>
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>
> > -----Original Message-----
> > From: Roman Black [SMTP:spamBeGonefastvid@spam@EZY.NET.AU]
> > Sent: Tuesday, October 24, 2000 1:07 PM
> > To:   RemoveMEPICLISTEraseMEKILLspamMITVMA.MIT.EDU
> > Subject:      Re: [EE]: best way to measure KWH
> >
> > Alan B. Pearce wrote:
> > >
> > > As you are trying to find where the power is being used, I suggest you
> > only need to measure current. Within a household the power factor should
> > be close enough to 1 for all appliances that the phase difference between
> > voltage and current will be minimal.
> > >
> > > The highest current path is going to be the one drawing the most power
> > unless you are running something like a welding transformer without power
> > factor correction.
> >
> >
> > Yep, I agree. Plus in a household environment the lights only draw
> > maybe 2% of the total current, "wacky" loads like PCs and electronic
> > devices maybe 10%, almost always electric heating is the culprit.
> > Running too many electrons through a wire until it glows hot is a
> > very crappy way to get heat, I think only 15% to 20% efficient
> > in most household devices.
> >
> I have always had the understanding that electricity to heat was one of the
> most efficient energy conversions you could get.  Incandescent lamps OTOH
> must be about the bottom of the ladder in terms of efficiency.
>
> Mike

>
> Looks like its time to check how my circuits are layed out.  Yeesh.
>
> So the ideal situation would drawing current off both lines at the same rate.
> If, for instance, you had two refridgerators you would want to set them up with
> an intelligent controlling system so that they would both be running at the same
> time when one needed cooling (as much as practical...).
>
> Of you could develop a converter (If you could make one efficient enough) which
> would take power equally from both phases regardless of the load you placed on
> either phase of its output.  Or I could just start buying equipment from the UK,
> setting all my PS's to 240, etc.  It's too bad they don't use the One True Power
> Line Frequency (TM) over there.  ;-)
>
> I suppose one could wrap two coils around the incoming mains lines, and hook
> them up in a configuration (similar to Ground Fault Protection circuits) such
> that a voltage will develop across two of the wires if the current draw on the
> two aren't even (and thus cancelling each other out).  You could measure that
> voltage and extrapolate the difference in current between the two as a simple
> "how much are we being charged for that we aren't using" indicator.  One could
> use a bi-color LED with voltage/current limiting to show which phase is drawing
> more current, with brightness showing how bad the situation is.
>
> Lots of fun here.  If it's bad at my place, it would be bad in the places around
> me.  I could set up a little business!  (Save $50 a year on your electric bill!
> I'll rearrange your circuit breakers for only $80!  ;-)  Of course I'm an
> electrician.  What?  Oh, well no, I'm not licensed, but *click*)
>
> -Adam

> > > -----Original Message-----
> > > From: Roman Black [SMTP:spamBeGonefastvidspam_OUTRemoveMEEZY.NET.AU]
> > > Sent: Tuesday, October 24, 2000 1:07 PM
> > > To:   .....PICLISTRemoveMEMITVMA.MIT.EDU
> > > Subject:      Re: [EE]: best way to measure KWH
> > >
> > > Yep, I agree. Plus in a household environment the lights only draw
> > > maybe 2% of the total current, "wacky" loads like PCs and electronic
> > > devices maybe 10%, almost always electric heating is the culprit.
> > > Running too many electrons through a wire until it glows hot is a
> > > very crappy way to get heat, I think only 15% to 20% efficient
> > > in most household devices.
> > >
>
> Michael Rigby-Jones wrote:
> > I have always had the understanding that electricity to heat was one of
> the
> > most efficient energy conversions you could get.  Incandescent lamps
> OTOH
> > must be about the bottom of the ladder in terms of efficiency.
> >
> > Mike
>

> Wow! In future I will be real careful how I phrase things! :o)
> Between you and Olin you are both perfectly correct. But I was not
> talking physics, I was talking about heating THINGS.
>
> Electric bar heaters, the most common, are very inefficient for
> heating the house. The heat energy may be very efficient at heating
> the coil of wire in the element, but useful heat radiated to
> a few feet away might be quite low. An electric bar heater with a fan
> to distribute the hot air is much better. A micro furnace heater
> which heats a small wire very very hot and then blows the super hot
> air around the room is even better.
>
> A stove element may be very eficient internally, but wastes a lot of
> heat energy radiated downward away from your frypan, more energy
> wasted heating the stovetop mass a few degrees, etc etc. An inductive
> stove top generates the heat in the frypan itself, and has a heat
> insulating stovetop so that the heat is kept in the frypan.
> Much more efficient, although this might not be as obvious when
> thinking about the theoretical models of the two designs.
>
> So if we are going to talk efficiency of household goods it might
> be smart to look at the power used vs actually what it achieves,
> rather than argue the perfect theoretical model.
>
> Since both yours and Olins arguments are perfectly correct I have
> to assume the fault was mine for not making it more clear exactly
> what the heck I was talking about! ;o)
> -Roman
>

>
> Well, after listening to the great ideas and comments, it appears that in order to
> meet my initial goal, I need to do the following:
>
> Place a CT type device on each leg in the box to measure current with a PIC at each
> location;
> Have one master box that monitors the voltage on the line with a second line
> transformer;
> Send the voltage sinusoid down one of the pins to all of the current monitor devices
> so that every one gets the v data
> (it is the same for all, after all). Sorry, two voltage waveforms, two legs.
> Let each node calculate real power or energy as may be the case
> poll the devices for their consumption data, and phase angle, et cetera back to the
> main unit
> Release the totalized data through a serial port to a WINTEL PC for display.
>
> Now all I need is time to do it all.  Anyone have any great ideas for that?
>
> Chris Eddy~
>
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>> >Almost all residential power in the US is single phase 220V with a
>central
>> >neutral. ie: you get 110V from neutral to each leg (which are 180 degrees
>> >apart) and 220V betweent the two hots. Stoves, dryers and other large
>loads
>> >are 220V, normal lighting and utility outlets are 110V on one leg.
>>
>> Isn't that two phase, not single phase?.
>
>No.  My house is a good example.  All three power phases get delivered to
>our neighborhood.  There is a transformer on the last power pole to my house
>which has a single primary winding that is driven from one of the three
>phases.  The secondary is center tapped, with the center grounded to a big
>copper bar sunk into the ground by the circuit breaker box in my basement.
>Each half of the secondary is 110V, which makes 220V accross the ends of the
>secondary.  The about half the 110V circuits are wired between one end of
>the secondary and ground, and the other half to the other end of the
>secondary.  The 220V drier circuit is wired from one end of the secondary to
>the other.
>
>Yes, I have two 110V "phases" in my house that are 180 degrees apart.  But
>from the power company point of view my house is fed completely from one of
>their three phases.

> > When I was at technical college, just opposite was a large sweet
> > factory, we were always told by the lecturers that they employed a man
> > solely to switch capacitors (huge ones!)
>
> Sounds like a job for a PIC <g> (must have been a union shop).
>
> > to keep the phase of their
> > consumption correct - failing to do so caused much larger bills as it
> > caused the meters to read high.
>
> Power companies often measure phase angle of large customers, and charge
> more as the phase angle goes up.  A large phase angle will not make the
> power meters read more because more power is not being delivered.  It will
> however, cause more current in the transmission lines to deliver the same
> power, which costs the electric company more, which they charge for.
>   Using a PIC: How do I measure the phase angle?