STANDARDIZATION RULES Ol 1 III: A.I.E.E. 



V. APPENDICES AND TABULAR DATA. 

 APPENDIX A. NOTATION. 



The following notation is recommended: 



Name of Quantity Symbol Unit 



324 Voltage, e.m.f., potential difference E, e, volt 

 Current / . ampere 

 Resistance R. r. ohm 

 Reactance A", x. 

 Impedance /. *, 

 Admittance Y, y, mho 

 Conductance G, t, 

 Susceptance H. o, 



Power P, p, watt 



Capacity ( '. < . farad 



Inductance L, henry 



Magnetic flux <t> maxwell 



Magnetic density gauss 



Magnetic force //. gilbert per cm. 



Length L, I, cm. or inch 



Mass M, m, gm. or Ib. 



Time T, t, second or hour 



Em, Im and Bm should preferably be used for maximum cyclic values, 

 e, i and p for instantaneous values, E and / for r.m.s. values (see 

 Sec. 5g.) and P for the average value or effective power. These distinc- 

 tions are not necessary in dealing with continuous-current circuits. 

 Vector quantities are preferably represented by bold face capitals. 



APPENDIX B. RAILWAY MOTOR 



(I) RATING. 



325 INTRODUCTORY NOTE ON RATING. Railway motors usually operate in 

 a service in which both the speed and the torque developed by the motor 

 are varying almost continually. The average requirements, however, 

 during successive hours in a given class of service are fairly uniform. On 

 account of the wide variation of the instantaneous loads, it is impracticable 

 to assign any simple and definite rating to a motor which will indicate 

 accurately the absolute capacity of a given motor or the relative capacity 

 of different motors under service conditions. It is also impracticable to 

 select a motor for a particular service without much fuller data with regard 

 both to the motor and to the service than is required, for example, in the 

 case of stationary motors which run at constant speeds. 



326 SCOPE OF NOMINAL RATING. It is common usage to give railway motors 

 a nominal rating in horse power on the basis of a one-hour test. As above 

 explained, a simple rating of this kind is not a proper measure of service 

 capacity. This nominal rating, however, indicates approximately the 

 maximum output which the motor should ordinarily be called upon to 

 develop during acceleration. Methods of determining the continuous 

 capacity of a railway motor for service requirements are given under a 

 subsequent heading. 



327 The NOMINAL RATING of a railway motor is the horse-power output at 

 the car-axle, that is, including gear and other transmission losses, which 

 gives A rise of temperature above the surrounding air (referred to a room 

 temperature of 25 deg. cent.) not exceeding 90 deg. cent, at the 

 commutator and 75 deg. cent, at any other part after one hour's con- 

 tinuous run at its rated voltage (and frequency, in the case of. an alter- 

 nating-current motor) on a stand, with the motor-covers removed, and 

 with natural ventilation. The rise in temperature is to be determined 

 by thermometer, but the resistance of no electrical circuit in the motor 

 shall increase more than 40 per cent during the test. 



