microcontroller AT89C51based power factor meter &correction

... but for current it is some wt complex can anybody help me

Usually one uses a series sense resistor (the current transformer works best at high currents, but doesn't know the DC current, which is important in a power-factor situation). Aim for a voltage drop of maybe 0.100 volts at full current rating. One can get 'isolation amplifiers' that can handle the line isolation issue, or you could make your own isolated power supply, use amplifiers and voltage/frequency conversion and optoisolators or transformers to connect to your microprocessor.

If full current is over 10A, the sense voltage times current can self-heat the series resistor, so some high currents are sensed using Hall effect sensors to probe the magnetic field around the conductor.

Read this!

Mit freundlichen Grüßen

Frank-Christian Krügel

"Power Factor" means the degree of mismatch between the current and voltage. This is often taken to just mean the phase mismatch between the sine waves, but for "real" power factor correction you should probably be monitoring the voltage and current out to the 5th harmonic (i.e. sample at 1000Hz) and doing some (gasp) real math.

If you're just interested in switching in reactive loads to correct that fundamental then you may be able to get by with your sine-to-square converter and timers in the chip, however.

As already mentioned, for the actual detection of volts and amps you can:

1. Use isolation amplifiers on voltage and current.
2. Run your whole circuit on the line side and simply step down the voltage then either use a current sense resistor, hall effect, or a current transformer and resistor to sense the current.