64 COMMERCIAL ELECTRICAL TESTING 



two series fields, one should be connected in each side 

 of the line. All other tests are made as on any direct 

 current generator. If unbalanced readings are required 

 the compensator should be wired according to diagram. 

 (Fig. 21.) 



A reading should be taken at no load, normal voltage. 

 With no change in the field, and holding constant 

 speed, j load should be thrown on one side of the 

 line, and the voltage read from the neutral to each 

 side of the line; volts and anperes field should also 'be 

 read. One-quarter load is then put on the other side 

 of the line, giving a balanced load, readings being taken 

 as before. The load is then increased to \ load on one 

 side, this procedure being continued until 125 per cent 

 balanced load is obtained, readings being taken at each 

 step. Instructions sometimes call for 50 per cent 

 unbalancing, in which case the load is increased 50 

 per cent at each step instead of 25 per cent. 



Standard Efficiency Test 



The method of calculating efficiency by the method 

 of losses is as follows: 



Consider a compound commutating pole generator. 

 Let VL = Volts line. 



CL = Amperes line = C& -\- C$ = C\$ + C\\ 



C G = Amperes, shunt field 



C 4 = Amperes, armature = Cjr,+C 6 



C & = Amperes, series field = CL r 



C 9 = Amperes, german silver shunt = CL 6' 8 



D 



Cio = Amperes, commutating pole field = CLTTF^ 



'(R 9 +R W ) 

 Cn = Amperes, commutating pole german silver 



shunt = CL~ C w 

 R 5 = Brush contact resistance 

 RS = Hot resistance of shunt field 

 7? 4 = Hot resistance of armature 

 R 8 = Hot resistance of series field 

 R 9 = Hot resistance of series field german silver shunt 

 RIO = Hot resistance of commutating pole field 

 RU = Hot resistance of commutating pole field 



german silver shunt 



