Digitize AC Voltage & Current Signals - Solutions for Split CT

[dvscrobe]

I am looking to digitize AC voltage and current signals that are measurements from my breaker panel. Any thoughts on what could be used to digitize the AC current? This current would be coming from split CT.

 

[berkeman]

Can you say more about your overall project? Is your goal to measure the power consumption of your home? If so, what-all kinds of power are you wanting to measure (Real, Reactive, etc.). Are you wanting to also measure harmonics and AC Line quality? To what accuracy?

Will you be monitoring the AC Mains input voltage plus individual breaker currents (how many?), or just one overall measurement of the input power for the whole panel?

What kind of computer resources do you have for monitoring this digitized data? What interfaces are available? (USB, Bluetooth, WiFi, etc.)

If you can say more about the number of V and I channels you need to digitize, and if you need to use synchronized sampling (for the various types of power measurements including power factor), and give us an idea of what computing resources you are going to use with this, that will be a big help.

Finally, do you plan to do the programming for this system, or would you prefer to use a canned HW/SW package that gives you a GUI and all of your data recorded for you?

 

[dvscrobe]

Can you say more about your overall project? Is your goal to measure the power consumption of your home? If so, what-all kinds of power are you wanting to measure (Real, Reactive, etc.). Are you wanting to also measure harmonics and AC Line quality? To what accuracy?

Will you be monitoring the AC Mains input voltage plus individual breaker currents (how many?), or just one overall measurement of the input power for the whole panel?

What kind of computer resources do you have for monitoring this digitized data? What interfaces are available? (USB, Bluetooth, WiFi, etc.)

If you can say more about the number of V and I channels you need to digitize, and if you need to use synchronized sampling (for the various types of power measurements including power factor), and give us an idea of what computing resources you are going to use with this, that will be a big help.

Finally, do you plan to do the programming for this system, or would you prefer to use a canned HW/SW package that gives you a GUI and all of your data recorded for you?

Hello Berkeman, I am looking for power consumption of entire home. Just the real power would be fine but having both real and reactive would be awesome. Don't care about harmonics or line quality. The accuracy should be to display to the nearest Watt and Var.

Computer resources? Well, I was hoping to use what I am hearing a lot about these days. A raspberry and Arduino. This is a capstone project idea I have proposed for my BSEET program. Getting the data to smartphone would be ideal but the criteria would simply be to transmit data wireless to any kind of remote display device.

The transducers I think would have to be an instrument PT for each 120V leg, a split CT on the return to ground to measure all phase to ground loads, and a split CT on one of the legs to measure all phase to phase loads. So, with that, I would need to digitize 4 signals. However, this will get me apparent power. Not sure how will I get real and reactive. I need something to measure phase angle and digitize that.

Not sure what synchronized sampling is. I have to avoid as much as possible kits because it is a capstone project. I have to do a lot of the work from scratch. My programming experience is limited to a Java course I took on Object Oriented Programming and a LabVIEW course on Graphical Programming. I am hoping the code to write is not that much.

 

[anorlunda]

Do you have three phase power in your home?

It sounds like you're making it more complicated than necessary. Can't you assume that the phases are balanced so that you need to measure only one?

Do you need instantaneous values or averages? If averages, over what period of time?

Do you really care about imaginary power?

You can calculate real and imaginary power from instantaneous V * I, no need to measure phase angles. But easier still to use watt meters and to sample less frequently.

What is your goal with this project? Do you want to improve efficiency? Do you want to track energy consumption down to each individual light bulb and cell phone charger? There are several ways to think of it. It would help if you tell us which.

You can buy whole house power monitoring systems for less than $150. Are you sure you want DIY?

Safety is paramount. The electrical/physical/environmental/abuse properties of the PT and CT installations need to be professionally designed. Do you have the qualifications to do that? Be aware that if you install stuff that violates applicable codes you might invalidate your home insurance.

 

[russ_watters]

Have you researched the commercial products that do this?

 

[dvscrobe]

Do you have three phase power in your home?

It sounds like you're making it more complicated than necessary. Can't you assume that the phases are balanced so that you need to measure only one?

Do you need instantaneous values or averages? If averages, over what period of time?

Do you really care about imaginary power?

You can calculate real and imaginary power from instantaneous V * I, no need to measure phase angles. But easier still to use watt meters and to sample less frequently.

What is your goal with this project? Do you want to improve efficiency? Do you want to track energy consumption down to each individual light bulb and cell phone charger? There are several ways to think of it. It would help if you tell us which.

You can buy whole house power monitoring systems for less than $150. Are you sure you want DIY?

Safety is paramount. The electrical/physical/environmental/abuse properties of the PT and CT installations need to be professionally designed. Do you have the qualifications to do that? Be aware that if you install stuff that violates applicable codes you might invalidate your home insurance.

Hello Anorlunda, I am a resident, so singe phase, not three phase. I need to be able to sample the voltage and current. For sake of a grade, I would be comfortable with just displaying real power. Reactive would be nice to have. The goal is for me to see on a remote graphical device (wireless) that shows real time Watts usage.

Since I am sampling, this display would update after a certain time period. I am thinking every 5 seconds would be nice. This is a Capstone project, so this project has to benefit society in some way using technological means. Therefore, the application would be for a homeowner to help analyze efficiency of major appliances. Track down to each light bulb? No. I would want to see whole consumption. So, if I had several loads going on (60 Watt bulb, 800 Watt toaster, and 400 Watt refrigerator), my graphical display would show 1260 Watts for the individual moment sampling took place. I just threw in those numbers as an example.

Buy systems and kits? Well, I would love to, but then I wouldn't get much of grade. Again, it's a capstone project. I appreciate the safety concerns you mention and will definitely take the home insurance mention into consideration.

 

[dvscrobe]

Have you researched the commercial products that do this?

Russ, Currently in process of doing that.

 

[berkeman]

The transducers I think would have to be an instrument PT for each 120V leg, a split CT on the return to ground to measure all phase to ground loads, and a split CT on one of the legs to measure all phase to phase loads. So, with that, I would need to digitize 4 signals. However, this will get me apparent power. Not sure how will I get real and reactive. I need something to measure phase angle and digitize that.

Not sure what synchronized sampling is. I have to avoid as much as possible kits because it is a capstone project. I have to do a lot of the work from scratch. My programming experience is limited to a Java course I took on Object Oriented Programming and a LabVIEW course on Graphical Programming. I am hoping the code to write is not that much.

I'm not sure that this project is a good match for your background so far. It would be a challenging project even for me, and I have lots of experience with AC Mains, data acquisition, DSP programming to process the digitized sensor signals, and even powerline metrology. With you not having much programming experience and not understanding synchronous sampling, that would tend to indicate that this project is not a good match.

And as @anorlunda says, working closely with AC Mains in the breaker panels can cause safety problems and invalidate your homeowner/renter insurance. And worse it could get you or others hurt.

Have you had any other ideas for your capstone project? Something that preferably does not involve AC Mains circuitry and connections?

https://www.skyfilabs.com/blog/good-capstone-projects-for-eee-students

 

[russ_watters]

Hello Anorlunda, I am a resident, so singe phase, not three phase.

Mine is split-phase, so it has 2 hots and I have 2 CTs. You sure yours is single-live single phase? Who is the target audience/market?

 

[dvscrobe]

Mine is split-phase, so it has 2 hots and I have 2 CTs. You sure yours is single-live single phase? Who is the target audience/market?

Russ, sorry, I think we are saying same thing. I have 240V service with a center tap. Target audience would be typical homeowner.

 

[Averagesupernova]

The transducers I think would have to be an instrument PT for each 120V leg, a split CT on the return to ground to measure all phase to ground loads, and a split CT on one of the legs to measure all phase to phase loads.

I think a CT on each hot will measure any current you need. You will get a better grade if you can demonstrate why you don't need to know neutral current if you know the current phasor for each hot.

 

[dvscrobe]

I think a CT on each hot will measure any current you need. You will get a better grade if you can demonstrate why you don't need to know neutral current if you know the current phasor for each hot.

Averagesupernova, yes, thanks. Had to think about that a little. Since real and reactive powers can be added to find total real and reactive power, I could measure the phase-ground voltage on one leg and the CT current on same leg to measure the 120V loads there, then do the same concept for the other leg. Then, for the 240V loads, I could measure the the phase to phase voltage along with the current on one of the legs. All real powers would get added, then all reactive powers would get added. I understand that installing split core CT's on energized main conductors would require asking for a disconnect from the power company by pulling the meter.

 

[berkeman]

I understand that installing split core CT's on energized main conductors would require asking for a disconnect from the power company by pulling the meter.

This is not correct. I'd tell you why, but at this point I don't want to encourage you to pursue this project.

 

[anorlunda]

I understand that installing split core CT's on energized main conductors would require asking for a disconnect from the power company by pulling the meter.

You're getting into an area that only licensed electricians can do. And they will do it only if it complies with the National Electrical Code.

This is a Capstone project, so this project has to benefit society in some way using technological means.

You're not going to benefit society if people break the law, or start fires, or get injured, or have to spend more money on an electrician than a commercial power monitor costs. Please heed the advice that @berkeman gave you. This is not suitable for a student project.

You should also know that many people can access data from their smart power meters at often as once every 30 seconds. They do that digitally by accessing the power company's web site. That can provide the same benefits as your project, and of course is it completely safe and legal.

 

[Averagesupernova]

Averagesupernova, yes, thanks. Had to think about that a little. Since real and reactive powers can be added to find total real and reactive power, I could measure the phase-ground voltage on one leg and the CT current on same leg to measure the 120V loads there, then do the same concept for the other leg. Then, for the 240V loads, I could measure the the phase to phase voltage along with the current on one of the legs. All real powers would get added, then all reactive powers would get added. I understand that installing split core CT's on energized main conductors would require asking for a disconnect from the power company by pulling the meter.

Ok. It's pretty clear you're in over your head here. I would think projects like this would have maybe one area that the person would be unclear with but based on what you've posted so far there are to many things you are not grasping. You would not do the CTs and PTs in the manner you describe. The hot-to-hot PT is redundant.

 

[berkeman]

@dvscrobe -- We are happy to help you with your projects, but as you can see from the multiple replies above, this AC Mains project is not a good idea for your capstone project. This thread is now closed.

If you would like to discuss a different capstone project, please feel free to start a new thread. Please stay safe -- we want you to be a healthy EE grad!