  We study the $q$-state Potts models on a cubic lattice in the thermodynamic
limit using tensor renormalization group transformations with the triad
approximation. By computing the thermodynamic potentials, we locate the
first-order phase transitions for $10 < q \le 20$ which has not been explored
using any method. We also examine the efficiency of the triad approximation
method in obtaining the fixed-point tensor and comment on how this can be
improved.
