How to find phase sequence in 3 phase system using micro controller without zero cross over?
The traditional way is to send two phases (scaled, of course) to a flip flop- one phase goes to the D input and the other phase goes to the clock input. (No third phase input is required.)

If the phase goes, say ABC, the clock going high will always occur first relative to the D input going high, so a LOW will be clocked in (since D is still LOW), and the flipflop output will always be LOW for ABC rotation. 

If the rotation is ACB, the D input going HIGH will occur first, and then the clock will go HIGH, causing the flop to clock in a HIGH on the output, signifying ACB rotation.

Go look at a graph of a 3-phase waveform. You'll be able to see the timing for when two adjacent phases are >0V, which correspond to the times when the above clocking occurs. You should be able to implement a digital comparator based on your read-in ADC values that can determine the sequence based on sequential peaks or numeric threshold crosses.