STANDARDIZATION RULES OF THE A.I.E.E. 



differs from 25 dcg. cent., correction on account of difference in resistant 

 should be made by changing the observed rise of temperature by one-half 

 per cent for each degree centigrade. Thus with a room temperature of 35 

 deg. cent., the observed rise of temperature has to be decreased by 5 per 

 cent, and with a room temperature of 15 deg. cent., the observed rise of 

 temperature has to be increased by 5 per cent. In certain casrs. such 

 as shunt-field circuits without rheostat, the current strength will he 

 changed by a change of room temperature. The heat-productioi 

 dissipation may be thereby affected. Correction for this should be made 

 by changing the observed rise in temperature in proportion as the 

 loss in the resistance of the apparatus is altered owing to the difference in 

 room temperature. 



270 3. BAROMETRIC PRESSURE. VENTILATION. A barometric pressure of 

 760 mm. and normal conditions of ventilation should be considered as 

 standard, and the apparatus under test should neither be exposed to draught 

 nor enclosed, except where expressly specified. The barometric pr 

 needs to be considered only when differing greatly from 760 mm. 



271 BAROMETRIC PRESSURE CORRECTION. When the barometric pressure 

 differs greatly from the standard pressure of 760 mm. of mercury. 



high altitudes, a correction should be applied. In the absence of more i 

 accurate data, a correction of one per cent of the observed rise in tempera- 

 ture for each 10 mm. deviation from the 760-mm. standard is recommended. 

 For example at a barometric pressure of 680 mm. the observed rise of tem- 

 perature is to be reduced by 8per O 



(II) LIMITING TEMPERATURE RISE. 



272 GENERAL. The temperature of electrical machinery under regular 

 vice conditions, should never be allowed to remain at a point at which 

 permanent deterioration of its insulating material takes place. 



273 LIMITS RECOMMENDED. It is recommended that the following maximum 

 values of temperature elevation, referred to a standard room temperature 

 of 25 degrees centigrade, at rated load under normal conditions of ven- 

 tilation or cooling, should not be exceeded. 



(A} MACHINES IN GENERAL. 



274 In commutating* machines, rectifying machines, pulsating-current 

 erators, synchronous machines, synchronous commutating machines and 

 unipolar machines, the temperature rise in the parts specified should not 

 exceed the following: 



276 Field and armature, 50 deg. cent. 



276 Commutator and brushes, by thermometer, 55 deg. 



277 Collector rings, 65 deg. cent. 



278 Bearings and other parts of machine, by thermometer, 40 deg. cent. 



279 (B) ROTARY INDUCTION. APPARATUS. The temperature rise should not 

 exceed the following: 



280 Electric circuits, 50 dcg. cent., by resistance. 



281 Bearings and other parts of the machine 40 deg. cent., by thermometer. 



282 In squirrel-cage or short-circuited armatures, 55 deg. cent., by thermo- 

 meter, may be allowed. 



(O STATIONARY INDUCTION APPARATUS. 



283 a. TRANSFORMERS FOR CONTINUOUS SERVICE. The temperature rise 

 should not exceed 50 deg. cent, in electric circuits, by resistance; ami in 

 other parts, by thermometer. 



284 b. TRANSFORMERS FOR INTERMITTENT SERVICE. In the case of trans- 

 formers intended for intermittent service, or not operating continuously 

 at rated load, but continuously in circuit, as in the ordinary case of lighting 

 transformers, the temperature elevation above the surrounding air-tem- 

 perature should not exceed 50 deg. cent., by resistance in electric circuits 

 and by thermometer in other parts, after the period corresponding to the 

 term of rated load. In this instance, the test load should not be applied 



