What would be the KW consuption of a 10 tonne, 3 phase Airconditioning plant? the relation between tonne & KW?

The number of phases of the power line is immaterial. A ten ton plant can move (by definition) 240,000 BTU/hr. You can use the Energy Efficiency Ratio to convert this number into kilowatts. A typical EER for such a plant would be about 9, so the power required (uming the machine is running at capacity all the time) would be 26.6 kW. (Just divide.)