310 SYNCHRONOUS MACHINES. [Exp. 



PART II. SYNCHRONIZING.* 



12. The motor (or other incoming synchronous machine) is 

 brought up to speed by an auxiliary motor or by whatever means 

 are provided. The field is excited with direct current which is 

 adjusted by a rheostat until the electromotive force E', generated 

 by the motor, is approximately the same as the line electromotive 

 force E, a close adjustment being unnecessary. When the motor 

 is running approximately at synchronous speed, the main switch 

 connecting it with the supply line is closedf at a moment when 

 the electromotive force E' of the motor is opposed to the electro- 

 motive force E of the line. The circuit should be protected by a 

 circuit-breaker or other device, for a large current would flow 

 if the switch should be closed when the two electromotive forces 

 are not opposed, or if the motor should fall out of step and stop, 

 in which case the line would be short-circuited through the 

 armature. 



13. Synchronizing with Lamps. There are various devices 

 for synchronizing, the simplest consisting of lampsj which bridge 

 the blades of the main switch with which the motor is to be con- 

 nected to the circuit. Fig. I shows such an arrangement for a 

 single-phase motor, or for one phase of a polyphase motor. 

 When the motor is running at the proper speed and is in the 

 proper phase for closing the switch, the lamps will be dark and 

 may remain so for a considerable interval. When the motor is 



* The same methods are used in synchronizing synchronous motors, 

 synchronous converters and synchronous generators operated in parallel. 

 Synchronizing by various methods should be practiced. 



fThe more inductance there is in the armature circuit, the less accurately 

 is it necessary to synchronize a machine before closing the switch. Extra 

 inductance, which may be cut out later, is sometimes introduced in the 

 armature circuit so that the motor may be thrown into circuit without 

 synchronizing, the inductance preventing excessive current while the motor 

 is pulling into step. 



i. For each lamp mentioned in the following paragraphs, several lamps 

 may be used in series when the voltage requires it. 



