486 



BELL SYSTEM TECHNICAL JOURNAL 



can be secured by throwing the switch to "distorted." The operation 

 of the circuit is then as follows: 



1. The commercial power supply is connected to the 10-volt windings 



of the transformers through balanced resistances which are so 

 proportioned that the voltage drop due to the magnetizing 

 current is sufficient to reduce the voltages across the windings 

 to about 10 volts. 



2. The resistances form such a large proportion of the total impedances 



presented to the incoming circuit that the currents through 

 the windings are controlled almost entirely by them and, since 

 they are non-inductive, this current has approximately the same 

 wave shape as the voltage of the power supply. Therefore, 

 since the magnetizing harmonics cannot appear to any large 

 extent in the magnetizing current, they appear in the voltage 

 across the transformers and the voltage wave is, therefore, 

 distorted. 



3. The distorted voltage wave on each transformer is stepped up 



between the 10 and 115 volt windings and is impressed on the 

 line at about 115 volts to neutral. 



DISTORTED NORMAL 



POWER LINE 



IN EXPOSURE 



AMr 



RESISTORS TO REDUCE 



VOLTAGE TO NEUTRAL 



TO 10 VOLTS 



Fig. 10 — Arrangement for comparing the inductive influence of balanced voltages 



of different wave shapes. 



Figure 11 is an oscillogram showing the "normal" and "distorted" 

 wave forms and it will be noted that they have about the same r.m.s. 

 values although the distorted wave is much more irregular indicating 

 the greater harmonic content. When the switch is thrown from "nor- 

 mal" to "distorted," the noise from the loud speaker increases and its 



