APPENDIX III 791 



The generator efficiency shall be determined for the values of load, power- 

 factor, temperature or other conditions existing during the turbine test. 

 When the generator is run during the turbine test at speeds different from 

 that used in the generator test, the generator efficiency shall be corrected 

 for the changes in speed. 



When practicable, the generator is to be separately excited during both 

 generator and turbine tests, and the excitation loss is not to be included 

 in computing generator efficiency, and is therefore also to be omitted in 

 computing turbine output during the turbine test. 



When determined by the separate-loss method, the generator efficiency 

 in the case of polyphase alternators when separately excited is to be taken as 



(Kilowatt Output at Generator Terminals) 



; Kilowatt \.IPR ar- \ . I ^ ""' \ . / Stray Load- 1 . J GeneratOT 1 



{ Output } + (mature / +CU ' core+ { iLes }+ da f I 



loss > land friction J 



all losses being expressed in kilowatts. 



The stray load-losses are to be determined, in accordance with Paragraph 

 458 of the above Standardization Rules of the A.I.E.E., by operating the 

 generator on short-circuit and at the current corresponding to the load to 

 be used in turbine test. This, after deducting the windage and friction and 

 I 2 R loss, gives the stray load-loss, the total amount of the loss so determined 

 being included in the above formula, in place of i or of this value as some- 

 times used in former practice. It is, however, understood that whenever 

 under the special conditions of an installation other losses exist, these are 

 to be added, in accordance with the second paragraph of this subdivision, 

 to the stray load-losses determined as here given. 



The value of generator windage and friction should be directly measured 

 in the shop, or after installation. In units containing direct-connected 

 exciters, the windage and friction may be measured by driving the generator 

 by the exciter run as a motor. When the windage and friction cannot be 

 directly measured, it is to be taken either from shop tests of generators of 

 similar design or from a retardation test made after installation. When 

 possible more than one method should be used in order to obtain a check. 



In making such a retardation test, the turbine shaft and runner, or the 

 turbine runner, are to be disconnected when practicable from the generator 

 shaft, in order to enable the windage and friction of the generator alone to 

 be computed. When the turbine shaft or runner cannot be disconnected, 

 the generator windage and friction are to be computed by deducting from 

 the total windage and friction that of the turbine, which for this purpose 

 may be found with sufficient accuracy from the formula: 



Turbine windage and friction in Kw. = KBD*N* in which 



B = height of distributor in feet; 

 D= entrance diameter of runner in feet; 

 N = revolutions per second; 



K = a,n empirical coefficient which may be taken as 0.000115 as deter- 

 mined from available test data. 



