Ministab and Sterostab regulate through a series transformer. A static control circuit drives the variable autotransformer that supplies the required voltage to the series transformer either in phase or phase Opposition to bring the mains to the rated value.

• The three-phase stabilisers are available in two versions:
  T models which regulate on the average of the three phases and are therefore suitable for balanced lines or for a maximum load unbalance between the phases of 50%.
  Y models that, having three separate control circuits, individually regulate each phase and are therefore suitable for unbalanced lines and load unbalance between phases up to 100%.