Behavior of synchronous motors during starting

The paper presents experimental data mainly in the form of oscillograms bearing on the subject of the paper. The oscillograms show very completely the effect on field current and armature current of a large number of combinations of starting conditions. From the oscillograms and curves, the following practical operating results are deduced: 1. That the effect of the closed field circuit on initial starting torque is negligible if low resistance damper windings of good design are used. 2. That with open field circuit during starting dangerous voltages are induced in the field winding. 3. That for all ordinary applications, at least, motors should be started with closed field circuit. 4. That successively larger loads can be pulled into synchronism if synchronism is attained: (a) On the starting voltage without excitation; (b) On the starting voltage with excitation; and (c) On line voltage with excitation. 5. That for moderate loads the minimum starting current is obtained by considerably over-exciting the motor before changing to line voltage. 6. That for large loads during starting and synchronizing, minimum starting current is obtained by under-exciting the motor before changing to line voltage. 7. Still further reduction in starting current is obtained by the use of reactance between the change from starting to line voltage, in which case excitation is delayed until the motor is in, or very near, synchronism.