The transformer is a two port. The left port voltage v1, left port current i1, right port voltage v2 and right port current i2 are connected by the following relation:
| v1 | | L1 M | | i1' | | | = | | | | | v2 | | M L2 | | i2' |
L1, L2, and M are the primary, secondary, and coupling inductances respectively.