1/4 ELEMENTS OF ELECTRICAL ENGINEERING. 



with a screw device for adjusting the tension of the belt by mov- 

 ing the machine back and forth on slide rails. 



81. General directions for starting. Before starting a dynamo, 

 generator or motor, see that the machine is clean, especially the 

 commutator and brushes. The metallic dust which comes from 

 the wear of the commutator and brushes is likely to make a short 

 circuit, and it should therefore be removed with special care. 

 Examine the whole machine closely to be sure that all screws 

 and contacts are tight. Fill the oil cups, adjust the oil feed, and 

 see that the oil ducts are clear. In the case of ring oiling bear- 

 ings, the rings should work freely and they should at all times 

 dip into the oil in the reservoir. See that the belt is in place and 

 has the proper tension. If it is the first starting of the machine, 

 it should be turned a few times by hand, or very slowly by power, 

 to make sure that the machine rotates freely, and that the belt 

 runs in the center of the pulleys. Examine the brushes ; see that 

 they press with sufficient pressure against the commutator, and 

 adjust them to the proper position by moving the rocker-arm. If 

 the proper position for the brushes is not indicated by a mark, this 

 last adjustment must be left until after the machine is running and 

 its field excited. Then the proper position of the brushes is 

 indicated by minimum sparking, and by maximum voltage in the 

 case of a generator, or minimum speed in the case of a motor. 



The machine should then be started and brought up to full 

 speed, gradually if possible, all switches, in the case of a generator, 

 being left open. While starting, the attendant should be in instant 

 readiness to stop if anything should seem to go wrong. 



82. Directions for starting and stopping a single shunt or com- 

 pound generator.* The arrangement of a single shunt or com- 

 pound generator for supplying current to lamps or motors is 

 shown in Fig. 69. In the starting of a single generator plant 

 like this the procedure is simple, there being no necessity for the 

 special precautions required in the starting and stopping of one 



* The management of the various types of series generators used for arc lighting is 

 described in special books of instruction issued by the manufacturers. 



