192 THE APPLICABILITY OF ELECTRICAL PROPULSION TO 



The turbo-generator furnishes power to the motors, the function of the gen- 

 erator and motors being solely that of a reduction gear. All changes of speed are 

 made by changing the speed of the turbine, thus varying the frequency of the gen- 

 erator, and consequently the speed of the motors, the reduction in this case being 

 eighteen to one, plus the slip of the motors. The motors are wound for only one 

 number of poles and therefore the speed ratio is not changeable as it would be for a 

 battleship installation; the reason for this is that such change is not necessary as 

 the cruising speed is practically the maximum speed. 



Speed changes are accomplished by means of a small control stand in front of 

 the switchboard. A small hand-wheel On this stand, working through a worm, 

 worm wheel, and set of bell crank levers, changes the position of the fulcrum about 

 which the governor acts, thereby varying the speed of the turbine. 



One of the three-phase windings from the generator is led to the two motors 

 direct. The other two leads are taken to the main switchboard, then through 

 "ahead" or "astern" oil switches, and then to the motors. 



Each motor is installed in a watertight pit which cannot easily be filled with 

 water from below. However, the motor windings are all made waterproof and 

 fireproof, and are intended to give safe running when partially submerged. The 

 rotor windings are connected to collector rings, which are in turn connected to the 

 water-cooled rheostats. These collector rings can be short-circuited by a slider, 

 operated by a lever and working on the motor shaft. The short-circuiting device 

 consists of a brass segment under each ring and a corresponding segment on the 

 slider. In addition to these devices there is an auxiliary device working with each 

 main device. The auxiliary consists of a carbon block on the solid segment and a 

 brass contact on the slider ; these contacts are held in place by flat springs on their 

 back and will thus be forced into contact before the main contacts are, and will 

 leave the carbon blocks after the main contacts have let go. The purpose of these 

 auxiliary contacts is to prevent the main contacts from being burned when oper- 

 ating the short-circuiting lever. These short-circuiting levers are locked, when in 

 the "resistance out" position, by electric solenoids in series with the field of the main 

 generator ; this prevents this lever from being moved out of this position while the 

 circuit is alive. It was found in the factory that excessive burning took place when 

 it was attempted to short-circuit the collector rings with full field on, and the lock 

 was put in to prevent this. 



There are two water-cooled rheostats, one for each motor, the total weight of 

 both being 5.8 tons. Each one consists of a top header, bottom header, three larger 

 porcelain cylinders at the bottom, three small porcelain cylinders on top of these, 

 and one noninductive resistance inside each of the large porcelain cylinders. These 

 resistances are made of calorite, and consist of spiral coils laid up on a wooden 

 spindle and having alternate coils connected oppositely from the others so as to 

 make the resistances noninductive. The large porcelain cylinders rest on rubber 

 gaskets on the bottom header, the resistances sit inside these cylinders, a rubber 

 gasket and a brass ring go on top of each large cylinder, and the small cylinders 



