L=4×10−4lnDmDsH/km
Mutual inductance
Dm=(Dab×Dab×Dab′×Da′b′)1/4
=(90×75×105×90)1/4=89.36 cm
Self inductance
Ds=(Daa×Daa′×Da′a×Da′a)1/4
Daa=Da′a=0.7788r=0.7788×1=0.7788cm
Ds=(0.7788×15×15×0.7788)1/4=3.417cm
L=4×10−4×ln(89.363.417)H/km
L=1.305mH/km.