Currents, flux linkages and electrical torques of a three phase machine closing on an infinite bus at any load angle

The currents, flux linkages, and electrical torques that result in the early stages of synchronizing a synchronous machine onto an infinite bus were examined. The problem applies primarily to a generator which is at sychronous speed prior to synchronization but which may be out of phase with the system to which it is to be connected. The problem is solved analytically (for small armature resistances) and by a digital computer program. The three phase machine is modeled with one amortisseur in each of the rotor direct and quadrature axes. The analytical results show that there is a net asymmetry in the transient unidirectional torque versus load angle (where load angle is defined as the initial phase angle across the machine breaker just prior to the synchronization attempt) characteristic. The net asymmetry is due primarily to the armature.