ELECTRIC OPERATIONS OF STEAM RAILWAYS 219 



The single-phase motor has the same characteristics and operates 

 exactly as the direct current motor and may in fact be operated 

 by direct current — a fact which constitutes one of its greatest ad- 

 vantages. It is, however, heavier for the same output and since 

 it, too, operates at low voltage, a stationary transformer is required on 

 the car or locomotive to reduce the high trolley voltage to the value re- 

 quired. This necessitates a heavier and more expensive motor equip- 

 ment than the direct current system and acts as an offset to the saving 

 effected in feeding conductors and sub-stations. In this system the 

 feeding conductor is the overhead trolley with catenary suspension and 

 the collecting device is the sliding trolley or pantagraph which is neces- 

 sary for very high speed and permissible by reason of the low values of 

 current required. 



The three-phase system owes its principal value to the fact that the 

 speed variation of the motor is very small throughout its full range of 

 tractive effort. As already stated, the tractive effort of the direct-cur- 

 rent and single-phase motors falls off with increasing speed, though not 

 so rapidly as that of the steam locomotive. Owing to this advantage, 

 the three-phase locomotive can maintain its high speed independently 

 of the grade. It operates without transformers on the car with trolley 

 voltages up to 5,000 and in coasting it returns power to the line auto- 

 matically, its motors acting as generators. It is, however, heavy per 

 unit of output and the system requires two trolley wires and is not 

 adapted to operation on the direct-current installations to be found in 

 many terminals. It has been adopted for one installation in this 

 country in which it is desired to increase the schedule speed on a long 

 mountain division. 



In this country the best engineering opinion seems to have united 

 in thinking that the single-phase system is the one best adapted for 

 future application to steam railways. This system is as yet only four 

 years old, yet there are at present over 1,000 miles of railways in the 

 United States operating under it and in this aggregate there are at 

 least five railroads formerly operated by steam. The system has proved 

 most successful in operation, although the first six months' operation 

 of the New York, New Haven & Hartford Eailroad have developed so 

 many unforeseen troubles, when applied to such a large enterprise, as 

 to bring upon it much adverse criticism. On the other hand, the high 

 degree of perfection to which the direct-current system has been 

 brought, the greater capacity of the motors of this system and the 

 enormous mileage already installed in tunnels and terminals have re- 

 sulted in a strong advocacy of this system. Speaking generally for 

 motors of equal weight, that of the direct-current system has 25 per 

 cent, more capacity than that of the alternating-current system. The 

 equipment of a high speed interuban car having four motors of approxi- 



