specially constructed transformer with a rotating primary coil that is
used to provide voltage regulation on individual power circuits. The
secondary of an induction regulator is mounted on the stationary shell
of cylindrical core, and the primary is mounted on a movable, center
rotor. In the neutral position, the magnetic axes of the primary and
secondary coils are oriented 90 degrees to each other, reducing the
magnetic coupling to zero. In this position, energizing the primary does
not induce voltage in the secondary; however, rotating the primary coil
in either direction from the neutral position creates mutual flux
linkage and causes a secondary voltage to appear.
Rotation in one direction causes secondary voltage to be in phase with the primary; rotation in the opposite direction causes secondary voltage to be out of phase with the primary. Voltage regulation is provided by connecting the primary coil across the line to be regulated and connecting the secondary coil in series with the load. By positioning the primary coil based on load demand in the line, secondary voltage can be used to adjust line voltage either up or down. Induction regulators are also equipped with a short-circuited coil mounted on the primary in spatial quadrature with the primary coil. In the neutral position, this coil has maximum coupling with the secondary coil, which minimizes the inductive reactance in the load line due to the secondary coil.