I'm developing one 3phase star delta starter in that starter I have to measure the 3phase voltage and display it in LCD so I need a circuit to measure 3phase voltage which can be interfaced with microcontroller,so I can measure the voltage and displays it,so I need a circuit and I will do coding according to that

 

Then presumably you need to measure both the delta condition between phases and the phase voltages to N or star, or between each star connected phase?
It could be done with matching instrument transformers but you may have a problem finding the right primary rating for a low secondary voltage required to interface to a micro.
You could also set up precision resistor divider on each phase with a low voltage tap to record the voltage ratio.
http://www.edn.com/design/test-and-measurement/4344950/Optocoupler-simplifies-power-line-monitoring
Max.

 

Then presumably you need to measure both the delta condition between phases and the phase voltages to N or star, or between each star connected phase?
It could be done with matching instrument transformers but you may have a problem finding the right primary rating for a low secondary voltage required to interface to a micro.
You could also set up precision resistor divider on each phase with a low voltage tap to record the voltage ratio.
http://www.edn.com/design/test-and-measurement/4344950/Optocoupler-simplifies-power-line-monitoring
Max.

Thank you sir..but I need measure voltage between each star connected phase

 

I need some more help..I have to measure 3phase voltage and I have give it to microcontroller and display it in lcd

 

Google using "digital voltmeter using pic micro controller"
The Microchip way would be one avenue to explore if you have ever used them.
https://www.google.ca/url?sa=t&rct=...k-eoBnZPg&sig2=N4McE6g2q7VlfGodk9cJsg&cad=rja
Max.

 

Do you really need to measure all three phases and display an average or can you just measure a single phase as being accurate enough and assume the other phases are identical or nearly so as they would be in most supply systems. This would make the problem much easier, a ready made commercial panel mounted voltmeter with suitable input rating connected across a pair of phases or a single phase transformer connected across a pair of phases with a low voltage output for measuring via a microcontroller. You could obviously repeat this single phase approach for all three phases if individual phases need to be simultaneously displayed.

However if you really need to measure all three phases and display an average value within a custom display you are probably going to have to go down the microcontroller route since as you will be aware if you try and use three transformers and connect their outputs in series in the hope of getting a summation the output will be zero (or therabouts) due to the vectorial summation of a (balanced) three phase network being nil. If using a microcontroller approach you could even measure the phase to neutral voltage, thus allowing the use of resistive dividers to a common neutral point, and derive the phase to phase values by mathematical manipulation.

 

Do you really need to measure all three phases and display an average or can you just measure a single phase as being accurate enough and assume the other phases are identical or nearly so as they would be in most supply systems. This would make the problem much easier, a ready made commercial panel mounted voltmeter with suitable input rating connected across a pair of phases or a single phase transformer connected across a pair of phases with a low voltage output for measuring via a microcontroller. You could obviously repeat this single phase approach for all three phases if individual phases need to be simultaneously displayed.

However if you really need to measure all three phases and display an average value within a custom display you are probably going to have to go down the microcontroller route since as you will be aware if you try and use three transformers and connect their outputs in series in the hope of getting a summation the output will be zero (or therabouts) due to the vectorial summation of a (balanced) three phase network being nil. If using a microcontroller approach you could even measure the phase to neutral voltage, thus allowing the use of resistive dividers to a common neutral point, and derive the phase to phase values by mathematical manipulation.

 

Thank you sir.

Google using "digital voltmeter using pic micro controller"
The Microchip way would be one avenue to explore if you have ever used them.
https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&ved=0ahUKEwidkJOUoo7TAhUI74MKHWK3BcgQFggtMAI&url=http://www.egr.msu.edu/classes/ece480/capstone/spring12/group03/Documents/Ryan_ApplicationNote.pdf&usg=AFQjCNH3bvXDDwY4f9p29vxIfk-eoBnZPg&sig2=N4McE6g2q7VlfGodk9cJsg&cad=rja
Max.