Can over-excited synchronus motor operate on lagging power factor?
I believe that a synchronous motor that is operating at a leading power factor is over-excited by definition and under-excited by definition if it is operating at a lagging power factor. If V > E, it seems to me that the motor must be acting as a generator and the definitions are reversed. The actual field current required to maintain unity power factor varies with load, so a given value of field current could be either over or under excitation depending on load.