ELECTRICITY METERS 



481 



An increase in frequency will also change the distribution and 

 the lag of the currents in the movable member and increase the 

 impedance of the disc. 



In the practical case a change of frequency upsets the lagging, 

 that is, the time-phase relation of the current and potential coil 

 fluxes, which has been adjusted at some standard frequency. 

 This being so, one would expect that the effects of a change of 

 frequency would not be very marked with loads of unity power 

 factor but might be considerable if the power factor were 

 low. Such is found to be the case; see Fig. 274 which also 

 shows the effect of an overload on the registration at normal 

 frequency. 



Induction Watt-hour Meter 



Effect of Wave Form 



Frequency=60 Cycles 



E =110 Volts 



1 = 9.3 Amps. 



I - Current and Voltage Waves Irregula 



TT - Current Wave Only Irregular 



1020304050607080901009080706050403020 

 Lag Power Factor Lead 



Fic. 27.",. L Showing effect of poor wave form on the registration of an 



induction meter. 



Effect of Wave Form. As the registration is affected by varia- 

 tions in frequency, one naturally expects that changes of wave 

 form will affect the accuracy of the meter, especially at low power 

 factors. This is shown by the curve, Fig. 275^4.. 



The theory of the induction wattmeter given on page 452 rests 

 on the assumption of sinusoidal waves of current, voltage and 

 flux. As the flux wave is the time integral of the voltage wave, 

 the form of the flux wave due to the potential coil will not be the 



31 



