Submeter design and calculations

Thread Starter

Dovid

Joined Jul 6, 2022
6
We are designing an electric submeter. We are looking for the calculations with the exact variables that we can collect from the voltage taps and current transformers to generate the kW used. For instance, if the CT gives us only amps, how do know how out of phase it is with the voltage to calculate power factor, etc.?

Thank you.
 

Jon Chandler

Joined Jun 12, 2008
261
Microchip and others have dedicated chips to so this that measure all the required parameters and calculate the resultant values. That's probably a good place to start.
 

Thread Starter

Dovid

Joined Jul 6, 2022
6
Microchip and others have dedicated chips to so this that measure all the required parameters and calculate the resultant values. That's probably a good place to start.
Yes, thank you. We want to build the the calculation/programming itself without using chips.
 

Ian0

Joined Aug 7, 2020
5,571
Yes, thank you. We want to build the the calculation/programming itself without using chips.
Without chips? That's ambitious.
To get the power you need to multiply the instantaneous voltage by the instantaneous current, then average the result.
"Without chips" would imply you are building a Gilbert cell out of transistors to do the multiplication, and I doubt you could meet the required standards for accuracy without a lot of adjustment.
If you mean "without microprocessors", then an analogue multiplier ICs don't come much cheaper than the AD633 at £15, and you can buy a handful of microprocessors for that price.
Microchip's dedicated electricity meter IC ATM90E26 will cost you £1.25
 

Thread Starter

Dovid

Joined Jul 6, 2022
6
Without chips? That's ambitious.
To get the power you need to multiply the instantaneous voltage by the instantaneous current, then average the result.
"Without chips" would imply you are building a Gilbert cell out of transistors to do the multiplication, and I doubt you could meet the required standards for accuracy without a lot of adjustment.
If you mean "without microprocessors", then an analogue multiplier ICs don't come much cheaper than the AD633 at £15, and you can buy a handful of microprocessors for that price.
Microchip's dedicated electricity meter IC ATM90E26 will cost you £1.25
We want to do it centralized, not in the field.
 

Papabravo

Joined Feb 24, 2006
18,839
Yes, thank you. We want to build the the calculation/programming itself without using chips.
That is going to be a tall order. Were you planning to resurrect the vacuum tube!!?
Sounds like what you have in mind is something to log the data and transmit it over some kind of data link.
 

Thread Starter

Dovid

Joined Jul 6, 2022
6
The following is the data from a meter in the field. We are looking for how they came up with (what is the equation/calculation) the kVA and PF which generated the kW.

No.Date/TimeV1V2V3I1I2I3KW L1KW L2KW L3Kvar L1Kvar L2Kvar L3kVA L1kVA L2kVA L3PF L1PF L2PF L3kWkvarkVAPFPF LAGPD LEADInFREQV UNB%I UNB%
1​
6/22/2022 16:34​
268​
270.3​
268.3​
4.17​
2.63​
3.95​
0.731​
0.616​
0.758​
0.503​
0.294​
0.283​
0.887​
0.683​
0.809​
0.824​
0.902​
0.937​
2.162​
1.1​
2.426​
0.891​
0.891​
1​
1.54​
60.02​
0.5​
28.6​
2​
6/22/2022 16:34​
268.3​
270.5​
268.6​
4.03​
2.53​
4.05​
0.732​
0.593​
0.834​
0.457​
0.3​
0.253​
0.863​
0.665​
0.872​
0.848​
0.892​
0.957​
2.094​
1.011​
2.325​
0.901​
0.901​
1​
1.36​
60.01​
0.5​
21.2​
3​
6/22/2022 16:34​
268.5​
270.5​
268.6​
4.09​
2.59​
3.89​
0.7​
0.622​
0.778​
0.484​
0.284​
0.226​
0.851​
0.684​
0.81​
0.822​
0.91​
0.96​
2.064​
1.038​
2.31​
0.894​
0.894​
1​
1.22​
60.01​
0.5​
26.2​
4​
6/22/2022 16:35​
268​
270.1​
268.3​
4.24​
2.71​
3.93​
0.737​
0.614​
0.758​
0.478​
0.33​
0.229​
0.878​
0.697​
0.792​
0.839​
0.881​
0.957​
2.193​
1.065​
2.438​
0.9​
0.9​
1​
1.3​
60.01​
0.5​
27​
5​
6/22/2022 16:35​
268​
270.3​
268.1​
4.05​
2.65​
3.89​
0.741​
0.614​
0.775​
0.483​
0.312​
0.273​
0.884​
0.689​
0.822​
0.838​
0.892​
0.943​
2.112​
1.066​
2.366​
0.893​
0.893​
1​
1.56​
60.01​
0.5​
24.1​
6​
6/22/2022 16:35​
268​
270.1​
268.3​
4.26​
2.71​
4.03​
0.714​
0.639​
0.791​
0.506​
0.268​
0.268​
0.875​
0.693​
0.835​
0.816​
0.922​
0.947​
2.111​
0.974​
2.325​
0.908​
0.908​
1​
1.54​
60.01​
0.5​
28​
7​
6/22/2022 16:35​
268​
270.3​
268.3​
4.07​
2.59​
4.01​
0.726​
0.599​
0.785​
0.499​
0.313​
0.249​
0.881​
0.676​
0.823​
0.824​
0.886​
0.953​
2.022​
1.169​
2.336​
0.866​
0.866​
1​
1.61​
60.01​
0.5​
24.5​
8​
6/22/2022 16:35​
268​
270.1​
268.3​
4.09​
2.69​
3.91​
0.7​
0.608​
0.754​
0.458​
0.288​
0.307​
0.836​
0.673​
0.804​
0.84​
0.905​
0.952​
2.111​
1.023​
2.346​
0.9​
0.9​
1​
1.5​
60.01​
0.5​
26.7​
9​
6/22/2022 16:35​
268​
270.3​
268.3​
4.19​
2.53​
3.89​
0.717​
0.614​
0.778​
0.505​
0.264​
0.239​
0.877​
0.668​
0.813​
0.818​
0.919​
0.956​
2.049​
1.01​
2.284​
0.897​
0.897​
1​
1.28​
60.02​
0.5​
26.5​
10​
6/22/2022 16:35​
268​
270.1​
268.3​
4.2​
2.53​
3.89​
0.686​
0.586​
0.74​
0.443​
0.303​
0.271​
0.816​
0.66​
0.788​
0.84​
0.888​
0.939​
2.109​
0.996​
2.332​
0.904​
0.904​
1​
1.38​
60​
0.5​
30​
 

Jon Chandler

Joined Jun 12, 2008
261
Yes, thank you. We want to build the the calculation/programming itself without using chips.
Since you seem to be a bit short of understanding what needs to be done, reading the datasheets for some of the power meter chips would help build that understanding. If you're trying to "roll your own", a thorough understanding of the principles involved will be needed.
 

Ian0

Joined Aug 7, 2020
5,571
Can you get a quantity discount on them?
I got them from ESRC vacuum tubes, who were in your neck of the woods (Orlando, to be precise) for $1 each. Sadly the firm no longer exist after the proprietor died. I wonder who bought all theirs stock
 

Ian0

Joined Aug 7, 2020
5,571
The following is the data from a meter in the field. We are looking for how they came up with (what is the equation/calculation) the kVA and PF which generated the kW.

No.Date/TimeV1V2V3I1I2I3KW L1KW L2KW L3Kvar L1Kvar L2Kvar L3kVA L1kVA L2kVA L3PF L1PF L2PF L3kWkvarkVAPFPF LAGPD LEADInFREQV UNB%I UNB%
1​
6/22/2022 16:34​
268​
270.3​
268.3​
4.17​
2.63​
3.95​
0.731​
0.616​
0.758​
0.503​
0.294​
0.283​
0.887​
0.683​
0.809​
0.824​
0.902​
0.937​
2.162​
1.1​
2.426​
0.891​
0.891​
1​
1.54​
60.02​
0.5​
28.6​
2​
6/22/2022 16:34​
268.3​
270.5​
268.6​
4.03​
2.53​
4.05​
0.732​
0.593​
0.834​
0.457​
0.3​
0.253​
0.863​
0.665​
0.872​
0.848​
0.892​
0.957​
2.094​
1.011​
2.325​
0.901​
0.901​
1​
1.36​
60.01​
0.5​
21.2​
3​
6/22/2022 16:34​
268.5​
270.5​
268.6​
4.09​
2.59​
3.89​
0.7​
0.622​
0.778​
0.484​
0.284​
0.226​
0.851​
0.684​
0.81​
0.822​
0.91​
0.96​
2.064​
1.038​
2.31​
0.894​
0.894​
1​
1.22​
60.01​
0.5​
26.2​
4​
6/22/2022 16:35​
268​
270.1​
268.3​
4.24​
2.71​
3.93​
0.737​
0.614​
0.758​
0.478​
0.33​
0.229​
0.878​
0.697​
0.792​
0.839​
0.881​
0.957​
2.193​
1.065​
2.438​
0.9​
0.9​
1​
1.3​
60.01​
0.5​
27​
5​
6/22/2022 16:35​
268​
270.3​
268.1​
4.05​
2.65​
3.89​
0.741​
0.614​
0.775​
0.483​
0.312​
0.273​
0.884​
0.689​
0.822​
0.838​
0.892​
0.943​
2.112​
1.066​
2.366​
0.893​
0.893​
1​
1.56​
60.01​
0.5​
24.1​
6​
6/22/2022 16:35​
268​
270.1​
268.3​
4.26​
2.71​
4.03​
0.714​
0.639​
0.791​
0.506​
0.268​
0.268​
0.875​
0.693​
0.835​
0.816​
0.922​
0.947​
2.111​
0.974​
2.325​
0.908​
0.908​
1​
1.54​
60.01​
0.5​
28​
7​
6/22/2022 16:35​
268​
270.3​
268.3​
4.07​
2.59​
4.01​
0.726​
0.599​
0.785​
0.499​
0.313​
0.249​
0.881​
0.676​
0.823​
0.824​
0.886​
0.953​
2.022​
1.169​
2.336​
0.866​
0.866​
1​
1.61​
60.01​
0.5​
24.5​
8​
6/22/2022 16:35​
268​
270.1​
268.3​
4.09​
2.69​
3.91​
0.7​
0.608​
0.754​
0.458​
0.288​
0.307​
0.836​
0.673​
0.804​
0.84​
0.905​
0.952​
2.111​
1.023​
2.346​
0.9​
0.9​
1​
1.5​
60.01​
0.5​
26.7​
9​
6/22/2022 16:35​
268​
270.3​
268.3​
4.19​
2.53​
3.89​
0.717​
0.614​
0.778​
0.505​
0.264​
0.239​
0.877​
0.668​
0.813​
0.818​
0.919​
0.956​
2.049​
1.01​
2.284​
0.897​
0.897​
1​
1.28​
60.02​
0.5​
26.5​
10​
6/22/2022 16:35​
268​
270.1​
268.3​
4.2​
2.53​
3.89​
0.686​
0.586​
0.74​
0.443​
0.303​
0.271​
0.816​
0.66​
0.788​
0.84​
0.888​
0.939​
2.109​
0.996​
2.332​
0.904​
0.904​
1​
1.38​
60​
0.5​
30​
To get power you multiply instantaneous voltage by instantaneous current and average the result.
To get VA you multiply average current by average voltage.
To get power factor you divide power by VA.
 

Papabravo

Joined Feb 24, 2006
18,839
I got them from ESRC vacuum tubes, who were in your neck of the woods (Orlando, to be precise) for $1 each. Sadly the firm no longer exist after the proprietor died. I wonder who bought all theirs stock
Some guy with an 8' table at a hamfest – no doubt
 
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