Fig. 2,849.—Diagram of Lincoln Synchronizer. In construction, a stationary coil F, has suspended within it a coil A, free to move about an axis in the planes of both coils and including a diameter of each. If an alternating current be passed through both coils, A, will take a position with its plane parallel to F. If now the currents in A and F be reversed with respect to each other, coil A will take up a position 180° from its former position. Reversal of the relative directions of currents in A and F is equivalent to changing their phase relation by 180°, and therefore this change of 180° in phase relation is followed by a corresponding change of 180° in their mechanical relation. Suppose now, instead of reversing the relative direction of currents in A and F, the change in phase relation between them be made gradually and without disturbing the current strength in either coil. It is evident that when the phase difference between A and F reaches 90°, the force between A and F will become reduced to zero, and a movable system, of which A may be made a part, is in condition to take up any position demanded by any other force. Let a second number of this movable system consist of coil B, which may be fastened rigidly to coil A, with its plane 90° from that of coil A, and the axis of A passing through diameter of B. Further, suppose a current to circulate through B, whose difference in phase relation to that in A, is always 90°. It is evident under these conditions that when the difference in phase between A and F is 90°, the movable system will take up a position, such that B is parallel to F, because the force between A and F is zero, and the force between B and F is a maximum; similarly when the difference in phase between B and F is 90°, A will be parallel to F. That is, beginning with a phase difference between A and F of zero a phase change of 90° will be followed by a mechanical change on a movable system of 90°, and each successive change of 90° in phase will be followed by a corresponding mechanical change of 90°. For intermediate phase relation, it can be proved that under certain conditions the position of equilibrium assumed by the movable element will exactly represent the phase relations. That is, with proper design, the mechanical angle between the plane of F and that of A and also between the plane of F and that of B, is always equal to the phase angle between the current flowing in F and those in A and B respectively. As commercially constructed coil F consists of a small laminated iron field magnet with a winding whose terminals are connected with binding posts. The coils A and B are windings practically 90° apart on a laminated iron armature pivoted between the poles of the magnet. These two windings are joined, and a tap from the junction is brought out through a slip ring to one of two other binding posts. The two remaining ends are brought out through two more slip rings, one of which is connected to the remaining binding post, through a non-inductive resistance, and the other to the same binding post through an inductive resistance. A light aluminum hand attached to the armature shaft marks the position assumed by the armature.
Ques. What is the action of the amortisseur winding?
Ans. Any sudden change in the speed of the field, generates a current in the amortisseur winding which resists the change of velocity that caused the current.
The appearance of an amortisseur winding is shown in the cut below ([fig. 2,850]) illustrating the field of a synchronous condenser equipped with amortisseur winding.
Fig. 2,850.—General Electric field of synchronous condenser provided with amortisseur winding. Hunting is accompanied by a shifting of flux across the face of the pole pieces due to the variation in the effect of armature reaction on the main field flux as the current varies and the angular displacement between the field and armature poles is changed. Copper short circuited collars placed around the pole face have currents induced in them by this shifting flux, which have such a direction as to exert a torque tending to oppose any change in the relative position of the field and armature. This action is similar to that of the running torque of an induction motor and the damping device has been still further developed until in its best form it resembles the armature winding of a "squirrel cage" induction motor. The pole pieces are in ducts, and low resistance copper bars placed in them with their ends joined by means of a continuous short circuiting ring extending around the field. Such a device has proven very effective in damping out oscillations started from any cause, the same winding doing duty as a damping device and to assist the starting characteristics.
Ques. How are three phase alternators synchronized?
Ans. In a manner similar to the single phase method.