500 



ELECTRICAL MEASUREMENTS 



a to d, operates the clutch, if direct-current meters are being 

 tested. With alternating-current meters, as shown in the figure, 

 the contact sector e is included in the potential circuit. In either 

 case, the power by the meter is 



P = WQK h N. 



Fictitious Loads and Arrangements for Phase Shifting. In 

 the laboratory it is often convenient, and sometimes necessary, 

 especially when meters of high capacity are tested, to avoid the 

 consumption of energy which would result from loading the meter 

 in the ordinary way. Also, in service tests after the meter 

 has been installed it is often necessary to test at definite loads 



Carbon storage Battery 4 V. 

 neo. 



FIG. 287. Connections for testing a watt-hour meter by use of a fictitious 



load. 



and under constant conditions. This is frequently impossible 

 if the customer's load is relied upon. It is not feasible to use 

 large rheostat loading boxes on account of their expense and in- 

 convenience. In such cases, the potential and current circuits 

 may be separately excited from two sources; the potential cir- 

 cuit from the line as usual and the current circuit from a low- 

 voltage source. 



For direct-current work, up to 500 amp., two Edison stor- 

 age cells and a compact carbon rheostat, as indicated in Fig. 

 287, are very convenient. By turning back the handle of the 

 rheostat, the circuit is broken when the readings are not being 

 taken. The weight of the cells for testing 500-amp. meters is 

 about 180 Ib. 



PROPERTY OF ELECTRICAL LABORATORY, 



FACULTY OF APPLIED SCIENCE. 





