if I am understanding you right, you have three sets of Z-values for identical X- and Y-axis but different respective values.
In that case, create a worksheet with three columns x,y,z, insert your values and create your ternary graph. After that add three more columns and insert your next set of data. Be sure to set the cloumn types to x2, y2 and z2 respectively. Then mark the new data and drag'n'drop it to your existing graph. Most probable you will have to double click on your data to define different colors, symbols etc to your new data set.