The phase shifter P controls an active power PMonitored to keep it in a certain desired [PMin;PMax] range. When the active power monitored goes above PMax or under PMin, the phase-shifter will act to modify its tap to bring back the active power in an acceptable range.
The time interval before the first time change is specified with a first timer and a second timer indicates the time interval between further changes. The automaton can be locked by an external controller: in this case, it stops acting.
The detailed phase-shifter P behavior is explained in the following state diagram:
.Dynawo.Electrical.Controls.Transformers.PhaseShifterP