200 PRINCIPLES OF ELECTRICAL DESIGN 



the accuracy of his estimate by satisfying himself that the 

 results obtained accord with the known laws of physics. 



Since the design of commutating poles was treated at some 

 length in the chapter on commutation (see Art. 51, Chap. VIII), 

 it is proposed to select for the purpose of illustration a machine 

 of comparatively small output, and endeavor to obtain satis- 

 factory commutation without the addition of interpoles. 



62. Design Sheets for 75-kw. Multipolar Dynamo. The 

 particulars contained in the following design sheets are more 

 than sufficient for the needs of the practical designer; but they 

 serve a useful purpose as a guide in making the calculations. 

 The items are numbered for easy reference, and it will be found 

 convenient to calculate the required dimensions and quantities 

 generally in the order given, although the particular arrange- 

 ment here adopted need not be adhered to rigidly. Two columns 

 are provided for the numerical values, and they are supposed 

 to be filled in as the work proceeds. The first of these columns 

 is to be used for assumed values or preliminary estimates; while 

 the last column is reserved for the corrected final values. 



The actual calculations will follow the design sheets, and 

 they will be shown in sufficient detail to be self-explanatory. 

 The calculation of items of which the numerical values are ob- 

 viously derived from previously obtained quantities will not 

 always be shown in detail. The design sheets should be fol- 

 lowed item by item, and where the method of calculation is 

 not clear, the succeeding pages may be consulted for explanations 

 and references to the text. 



The machine to be designed is for a continuous output of 

 75 kw. The terminal voltage on open circuit is 220; but it is 

 required to raise this to 230 at full load in order to compensate 

 for loss of pressure in cables between the dynamo and the place 

 where the power is utilized. The machine is therefore over- 

 compounded. It is to be belt-driven at a constant speed of 

 600 revolutions per minute. The temperature rise is not to 

 exceed 40C. after a full-load run of not less than 6 hr. duration. 



All numerical calculations have been worked out f on the slide 

 rule, and scientific accuracy in the results is not claimed. 



'CRY, 



OF APPLIED SCIENCE. 



