Discussion on “the behavior of synchronous motors during starting” (Newbury), “commutating pole saturation in direct-current machines” (Stokes), “constant voltage transmission” (Dwight) and “the industrial

William J. Foster: The self-starting synchronous motor has one bad characteristic and that is the induced potential across the field terminals. It is something which exists in the nature of the apparatus. Of course, if we keep down the number of turns in the field winding, we always can help out in the matter of induced potential, but, as is stated by Mr. Newbury, it is not always convenient to do this. As a general rule, 125 volts has been regarded as standard, and we can design and wind the fields and insulate them so as to take care, ordinarily, of 125-volt windings, but when it comes to 250 volts it begins to be a serious matter. The insulation problem is serious. In such cases I have known of this scheme of short circuiting the field to have been the practical solution of the problem, but in general, as pointed out by the author, the short circuiting of the field detracts from the starting torque per input. That being the case, it is extremely desirable to excite at lower potential.