CHAPTER V 



HEATING OF ELECTRICAL MACHINES- 

 ACTUAL LOAD TESTS 



The test to determine the heating of a machine is 

 a very important one and great care must be taken 'to 

 obtain reliable temperatures. Any large machine 

 requiring a considerable amount of floor space should 

 have the room temperatures taken at four different 

 points nearby, and at a sufficient distance away from 

 the machine to be unaffected by heat from the latter. 

 Two thermometers, one in air and one in a specially 

 designed metal cup containing oil, are used at each 

 point to measure the room temperature. Before starting 

 a heat run, thermometers should be placed on all im- 

 portant accessible stationary parts, such as series and 

 shunt field spools, pole tips, frame, etc., in the case 

 of a direct current machine. In addition, thermometers 

 should be placed between pole tips to register the 

 temperature of the air thrown off from the surface 

 of the armature and from the air ducts. Each ther- 

 mometer should be attached with the bulb in contact 

 with the part of which the temperature is required, 

 the bulbs being covered with putty. Thermometers 

 which are to register the temperature of air ducts 

 should be so placed that the bulb cannot make contact 

 with the iron laminations while the machine is running. 



The machine should be shielded from currents of 

 air coming from adjacent pulleys and belts. Unreliable 

 temperatures are obtained when the machine is located 

 so that another machine blows air upon it. A very 

 slight current of air will cause great discrepancies in 

 heating; consequently either a suitable canvas screen 

 should be used to shield the machine under test, or the 

 machine causing the draught should be shut down. 



[36] 



