ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 3 
4AZR. 
423. 
424. 
425. 
S,, at the moment both lamps show their maximum 
brilliancy. | 
4. After the switch S, is closed, the load may be grad- 
_ ually put on the motor and when the average load is ob- 
tained, the excitation should be so regulated, that the 
armature current becomes a minimum, which can be ob- 
served on the ammeter 4,. 
Stopping of Synchronous Motors.—tThe stopping 
of the motor involves the following operations: 
1. Gradual taking off of the load. 
2. Regulating the excitation to its minimum. 
3. Quick opening of the main switch S.. 
4. Inserting of all the resistance in the rheostat R,. 
5. Slow interruption of the excitation circuit by means 
of the switch S,. 
Characteristics.—A synchronous motor can be ad- 
justed to have a power factor equal to unity, that is, to 
bring the terminal pressure and the armature current 
in phase. This condition will be obtained for a certain 
excitation and if the field is wnder excited, the armature 
will carry a lagging current; or if the excitation is higher 
than that corresponding to a power factor of unity, the 
armature will carry a leading current. 
This feature of the synchronous motor is a most valuable one, 
as it can be used for improving the power factor of the 
line, the leading current having the same effect as a 
condenser in the circuit. 
Desirable Features.—It is desirable, that with 
slight changes in the excitation, noticeable pressure 
alterations should take place; therefore, as will be seen 
later, it is an advantage to work on the part below the 
knee or bend of the no-load characteristic curve. 
Speed.—The speed of a synchronous motor is absolutely 
constant if the prime mover of the supply generator 
maintains a constant speed, but any irregularity in the 
