Aim:
This project is to make high efficient digital three phase volt meter , with following specification using micro controller

Accuracy (+ or -) 0.25% F.S. (+ or -) 1 digit
Sampling Time Abt. 0.8 sec. typically
Aux. power source AC 110/220V (+ or -) 10%m 50/60Hz
Power Consumption <AC 3 VA
Operating Temp. range 0-60 deg. C
Storage Temp. range -10 -70 deg. C
Temperature coefficient <100PPM/deg. C
Max. relative humidity 95%
Dielectric strength (IEC688)
AC 2KV/1Min
Input/power/output terminals
AC 3KV/1min
All terminals to case
Impulse (IEC 255-4) Common mode 1.2 x 50 micro-sec
4KV
Display 14.2mm (0.56") H red LED

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i suggest you people need to read
http://circuitstodayac-voltmeters and http://elec-toolboxusefulinfo/xfmr-3ph.htm

i want this project please send me it's all information

In electronic ac voltme­ters input signal is firstly rectified and then sup­plied to the dc amplifier. In some circuits, the block diagram includes the attenuator, the rectifier and the multi-stage DC amplifier. and finally the output is shown in the PMMC meter. Sometimes, the block diagram will be attenuator->multistage amplifier, rectifier and PMMC meter.

AC voltmeters are divided into:
Average Reading AC Voltmeters.
They are average responding type and indicates the average value of the voltage on the dial. This method is effective and works satisfactorily and is less expensive beccause most of the systems involves the sinusoidal waveform. But in the case of the non-sinusoidal waveform voltage, the high or low waveform is given depending on the form factor of the waveform.

Implementaation:

Use a 220 to 6 V transformer which is then rectified and filtered to give the 6V dc . To adjust the voltage, a voltage divider circuit is used. Then give it to ADC to use the microcontroller to read the voltage and display in the LCD.

http://8051projectsforum-t31555.html
http://circuitstodayac-voltmeters