How to measure AC energy flow

[mrbean]

Is it possible to measure the direction of flow of AC power (Watts). I'm not really sure if that's the correct way to ask my question, so here's an example of what I mean.
If you have a microgeneration setup, solar/wind/hydro, and it's producing more Watts than your total household appliances are using at that moment in time, is it possible to detect that power is flowing back to the grid, rather than from the grid to your house.
It obviously possible in some respect as the old mechanical style meters will spin backwards. IS it possible to monitor the Watt usage of the house and be able to differentiate between power coming in from the grid as well as excess power flowing the other direction back to the grid. Ideally I would like to use a current sense resistor/shunt via an op-amp to a micro-controller.

Thanks for any advice.

Terry.

 

[karesz]

Hi Terry,
Shortly=yes!
You can build/buy so called +/- current sensors (as you say: a sensing resistor and a bipolar OpAmp...), & if you knows the (grid) voltage; rets is question of your SW...
Greetings!
K.

 

[mrbean]

That IC looks good, but I'm having a hard time trying to find somewhere I could purchase one. I might look into building something with a shunt and bipolar op amp. I'm not all that knowledgeable about electronics, but I learn fast and google is my friend. If anyone has any advice for parts or schematic examples, all and any help is appriciated.

Thanks.

 

[karesz]

Hi,
The vendor,Isabellenhütte, has international or global delivering...
Another (semiconductor)IC-family, as bipolar I-sensors, are ACS...(special models I will/can tell for you tomorrow) & some OpAmp after them.
The 3th possibility is: you will take an discrete current sensing resistor, instrumentations Amp and scaling (another OpAmp)for the uP`s onchip ADC...
In all "active" sensing circuit techniques BE CARE pls WITH MAINS voltages & apply robust separations/isolations!! For supplying your Amps too.... Dead isnt reversible :-(.
Good progress!
K.
P.S.:
A 4th possibility: Current transforming sensors from LEM, you can select/order it from Farnell...

 

[karesz]

Hali Terry,
Also,
1, Sensresistor Isabellenhütte_ **broken link removed** ,Disributors: https://www.isabellenhuette.de/en/precision-currentsensing/
2, sensresistor + INA138/139/169 for "high side,unipolar, current shunt monitor", refer pls to Figures 5...7 for bipolar & pwr measurements. All in SOT23 (SMD Transistor) packaging.
I remember for an InstrAmp with High-Ohm Input Attenuators for (I think) 200V CommonMode Input, but cant find yet...
3, ACS712, https://www.allegromicro.com Fully Integrated,_HAS "ON CHIP" SENSING RESISTOR!_Hall Effect-Based Linear Current Sensor IC with 2.1 kVRMS Voltage Isolation and a Low-Resistance Current Conductor (In SO8 package). I believe-thes is a super component for your & similar apps ...
4, LEM Voltage & Current transducer, i.e.: LV 25-P & HX 10NP_"DC, AC, pulsed, mixed, with a galvanic isolation between the primary circuit (high power) and the secondary circuit (electronic circuit).
**broken link removed**
Good luck!
K.

 

[FvM]

Current transducers (either regular core type or rogowski coil) are another simple method. to attach the measurement. Independant of the current measurement method, you need a real power measurement circuit (V * I multiplier and low pass filter) to determine the energy flow