I'm solving problems on the alternator and some of them give a reactance Xq in addition to the usual synchronous reactance Xd. Does anyone know what this Xq is?
I believe q- and d- refer to machine rotor coordinate system axis (that are rotating with the rotor). This means the alternator has a different reactance in one than in the other direction (if it has salient poles obviously this has to be the case!).
See this page for further explaination of the dq coordinate system.