synchronous motor leading pf

[mikeybmdb32]

Can anyone explain theoretically how a synchronous motor can be changed from a lagging to leading power factor? I understand that it can be done by adjusting DC excitation, but I don't understand how a device consisting of resistance and inductance can draw a leading PF.

 

[richxtlc]

Think of it as a generator, they are similar in construction, except that the generator has an output and the synchronous motor draws it power from the system. Just as in a generator, you can change the power factor by over or underexciting the field.