For lagging power factor = (IR*cosφ + Ixsinφ)/Vr For leading power factor = (IR*cosφ - Ixsinφ)/Vr Zero voltage regulation occurs on leading power factor only.
The series electromagnet is energized by a coil known as current coil which is connected in series with the load so that it carry the load current. The flux produced by this magnet is proportional to and in phase with the load current.
EXAMIANS