\M>.\Rl>l/..\llt>S RULES OF TV/A A I E.E. 



(II) SELECTION Of MOTOR FOR SPECIFIED SERVICE. 



328 GENERAL REQUIREMEMTS. The futubthiy of railway motor for a 

 specified service depends upon ibe following considerations: 



329 ; Mechanical ability to develop the requisite torque and 



its speed- torque c : 



330 fc. / te successfully the current AmftMH 



331 t Ahihty to ojK-rMr in service without occasioning a 



l endangr 



332 | operating conditions which 

 are importan ,f a motor include the weight of load, the 

 schedule speed, the -I. stance between stops. tl. n of stops, the 



of acceleration and of braking retardation, the grades and the curve*. 

 with these data at hand, t) re required of the motor may 



be determined, provided the srr mis are within th- 



petd-toraue curve of the motor. These outputs may be nip rusted 

 Of curves givin* the instantaneous values of current and of 

 nt be applied to the motor - may b< 



line, hut they are usually - 1 only for ft O 



average or typical run. which it fairly representative of the conditions of 

 service. To determine whether the motor has sufficient capacity to per- 

 form the service safely, further tests or investigations must be made. 



333 IK is M The capacity of a 

 railway -he necessary output may be determined by 

 measurement of its temperature after it has reached a maximum in ser- 



a running test cannot be made under the actual conditions of 

 service, an t lest may be made in a typical run back and forth, 



under such conditions of schedule speed, length of run. rate of acceleration. 



the test cycle of motor losses and conditions of ventilation are 

 essentially the same as would be o 1 a the specified serv 



334 MKIH-' v \\\ ui in SERVICE REQUIRE- 



is not convenient to test motors under actual service 

 is or in an equivalent typical run. recourse may be had to one of the 

 two following methods of determining temperature rise now in general 

 use: 



336 1 in !.os,. \PAcm ri-RVB*. The heat de- 



railway motor is carried partly by conduction through the 

 several parts rough the air to the motor-frame 



whence it is distributed to the outside air. As the temperature of the 

 several parts is thus dependent not only upon their own internal losses 

 but also upon the temperature of neighboring parts, it becomes necessary 

 to determine accurately the actual value and distribution of losses in a 

 railway motor for a given service and reproduce them in an equivalent 

 run. The results of a series of typical runs expressed in the form of 

 thermal capu the relation between degrees rise per watt 



loss in the armature and in the field for all ratios of losses between them 

 met with in the commercial application of a given motor. 



336 1 his method consists, therefore, in calculating the several internal 

 motor losses in a specified scr\ nperature rise 

 with these losses from thermal capacit -:g the degrees rise 

 per watt loss as obtained in experimental track tests made under the same 

 conditions of ventilation. 



337 The following motor losses cause its heating and should be carefully 

 determined for a given s<r R in the field: 7 1 R in the armature: 

 /' R in the brush contacts, core loss and brush fn 



338 The loss in the bearings (in the case of geared motors) also adds some- 

 what to the motor- heating, but owing to the variable nature of such 

 losses they are generally neglected in making calculations. 



339 MOD uv < M VMM OF MOTOR. The essential losses 

 in the motor, as found in the typical run. are in most cases those in the 



