116 COMMERCIAL ELECTRICAL TESTING 



Input-output efficiency test is made by the input- 

 output method. 



Standard efficiency test is made by the method of losses. 

 The calculation of a standard efficiency test is made as 

 follows : 



Let VL = volts line 



Wi = output = A/3 VL CL for three-phase and 



2 VL CL for two-phase 

 CL = amperes line Ri = hot res. of armature be- 



tween lines 

 C\ = amperes field 

 R 2 =hot res. of field 

 Wi =open circuit core loss corresponding to VL+ 



CR on the core loss curve 

 W 2 = short circuit core loss corresponding to CL 



on the short circuit loss curve 

 Wz friction and windage obtained from core 

 loss test 



C\is calculated for each load, as in the test for regulation. 

 CR = the drop in the armature = \/f CL RI for three- 

 phase machines and CL RI for two-phase. 



= WVf i Ws+WVhJ C L Ri+CS R 2 for three- 



phase machines 



= Wi+ i Wi+Wt+2 C L *Ri+Ci*Rt for two- 

 phase machines 

 Watts input = W a 



Efficiency = -^ 



W a 



WB need not be considered if the machine is furnished 

 without base, shaft or bearings. 



The above method of calculation is used when the 

 machine is to operate at unity power-factor. 



If it is desired to calculate the efficiency at any power- 

 factor, the following calculations must be made : 



Kw. 



C L = ~ and 



FLX\/3X%P-F. 



W b = V3 X V L X C L X % P-F. for three-phase machines 

 Kw 



l/ L X2X%P-F. 



and 



