PRACTICAL OPERATION OF DYNAMOS. 1/3 



A dynamo should be kept perfectly clean and dry, and it should 

 not be exposed to dust. A water-proof covering should be 

 thrown over the machine when it is not in use. 



When a dynamo, generator or motor, is started for the first 

 time (or after it has been standing unused for a long time), it 

 should be very closely watched for an hour or more, inasmuch as 

 an unexpected defect may develop. 



If there is the remotest possibility that a generator is wet or 

 even moist, it should be driven for several hours without exciting 

 its field ; the idea being to accelerate the drying process by the 

 fan-like action of the rotating armature, The field is then to be 

 gradually and cautiously excited by cutting out resistance in the 

 field rheostat, and finally the current output is to be cautiously 

 increased to its full rated value. 



When a motor has been exposed to dampness it should be run 

 as a generator and treated as above described, the idea being to 

 drive the machine for a number of hours and dry it thoroughly 

 before any electromotive force is brought into action between the 

 various windings. In the case of an isolated motor, however, 

 it is not feasible to drive it as a generator. If the machine* is very 

 damp it should be dried by gentle and long-continued heating. 

 In many cases, however, it is allowable to excite the field of the 

 motor, start it, and run it for several hours on zero load ; the 

 motor may then be gradually loaded until full load is reached. 



Unless a dynamo is positively known to be dry it must be 

 assumed to be moist and treated accordingly. A new machine 

 may become damp in transit from the factory. 



In the opening of a switch a destructive arc or spark is likely 

 to be formed, especially if the current is large, or the inductance 

 of the circuit is high, as in the case of a field winding. Properly 

 constructed switches have carbon blocks so arranged as to take 

 this arc or spark off the metal parts of the switch, thus lessening 

 the wear on the switch. In any case a switch must be opened 

 and closed with a vigorous and unhesitating movement. 



A belted dynamo, generator or motor, should be provided 



