SYNCHRONOUS MOTORS IN LOCAL DISTRIBUTION 59 



to charge for them separately and at a rate of, say, 

 one-fourth of the rate for the Kw.-hours. 



The metering of the reactive Kva.-hours is accurately 

 done by using a special, simple connection of a standard 

 3-phase watt-hour meter, as shown in Fig. 8.* On 

 comparing it with the regular connection for energy 

 measurement, Fig. 7, it is seen that the only differences 

 are that in Fig. 8 the connections to the shunt coils of 

 the two elements are interchanged and the connection 

 to one of the series coils is reversed. In Fig. 7 the current 



FIG. 7. Energy 

 Measurement. 



FIG. 8. Reactive Energy 

 Measurement. 



and voltage of each element are 30 out of phase at 

 unity power-factor, and in Fig. 8 they are 90 out of 

 phase, and so register zero at unity power-factor. The 

 readings of the meter in Fig. 8 are multiplied by a 



Vs 



constant, , to obtain the reactive Kva.-hours, when 



the same scale and transformers are used for the two 

 meters shown. 



A bonus for high power-factor, such as is given by 



* "Watt-hour Meters," by C. W. Baker, The Canadian Electrical 

 News, July, 



