Unbalanced Load Lose Calculation

Your 3 phase meter does not know, nor does it care, about the degree of imbalance, it will still only record the amount of energy consumed. Your utility might though, and charge you a penalty for being severely unbalanced. Unbalanced loads can also lead to poor power factor, another area where you can be penalized by the utility. As PWS pointed out, only the tariffs will tell you if this is the case.

The place where an "extra" charge might occur is through the extra heating that your motors might be experiencing as a result of the imbalance, and the additional loss of life that the heating may be causing. Calculating this is problematic, it's much easier to take Lyn's suggestion and actually measure the difference between balanced and unbalanced operation at the same mechanical loading. Rent a power quality meter and balance your loads, and/or hire an electrical engineer to guide you.