Tesla's invention is, in essence, a rotating transformer. Its primary windings reside in a stationary steel casing (the stator) and and secondary conductors are attached to an inner shaft (the rotor).
Think of it as a rotating transformer, with the primary windings residing in a stationary casing (stator) and the secondary conductors attached to an inner shaft (rotor).
In this paper the effects of gland leakage on the secondary flow and outlet flow fields in the governing stage stator cascade of a 300mw turbine set are simulated numerically.