596 ELECTRICAL EQUIPMENT 



total impedance would be equal to A/50 2 +1000 2 = 1000 ohms 

 approximately. With 100,000 volts impressed on this circuit 



i no non 

 the current flow would be - ' =100. If now in addition 



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the circuit contains an inductive reactance of 1000 ohms, it is 

 evident that this entirely neutralizes the capacity reactance and 

 that the current is only limited by the 50-ohm resistance, thus 



100 000 



in this case equal to ^ = 2000 amperes. With this current 

 ou 



flowing the voltage across either the inductance or capacity be- 

 comes equal to 2000X1000 = 2,000,000 volts, which of course 

 would be far beyond destruction. Of course, this extreme con- 

 dition does not apply to an ordinary transmission line where the re- 

 sistance, inductance and capacitance is distributed, but destruc- 

 tive voltages may be set up where inductance and capacitance 

 is concentrated. 



Fortunately, the characteristics of transmission systems are 

 such that their inductive reactance is not large enough to neu- 

 tralize the capacity reactance at the fundamental generator 

 frequency. Since, however, the inductive reactance increases 

 and the capacity reactance decreases proportionally to frequency, 

 the two reactances come nearer together for high frequencies, 

 such as for the high harmonics of the generator wave. These 

 may, therefore, be the cause of resonance rise of voltage between 

 the line capacity and circuit inductance. With modern alterna- 

 tors, however, the higher harmonics are generally so small that 

 there is not much danger from resonance. 



Abnormal voltages can also be caused by traveling waves 

 which are set up when the equilibrium of an electric circuit is 

 disturbed. Such disturbances may originate in the circuit itself 

 as by switching or they may be due to external causes, such as 

 atmospheric lightning phenomena. 



When an electric circuit is connected to a generator or other 

 source of energy, a wave of voltage and current shoots out along 

 the line with a very high velocity and charges the same. If the 

 maximum value of the voltage is e and the maximum value of the 

 current i, the wave possesses per unit length an electrostatic 



s~i -2 T *2 



energy of watt seconds and an electro-magnetic energy of -|- 

 watt seconds, C being the capacity in farads and L the inductance 



