I don’t think I have ever seen a VD calculated like that.

This is how I was taught:

VD= (2*L*I*K)/CM

K = 12.9 for CU and 21 for Al
CM for conductors on Table 8 NEC 2006 (pp70-635)

2 x 100 x 16 x 12.9/6530 = 6.32V

Note 3ph is a little different.

101° Rx = + /_\