OVER-VOLTAGE PROTECTION 599 



In the above it was assumed that the end of the line was either 

 open- or short-circuited. If a non-inductive resistance, R, is 

 connected across the end of a line, the voltage of the reflected 

 wave, and thus the total voltage at this point, necessarily depends 

 on the value of this resistance. When R = oo it naturally resem- 

 bles an open-circuit in which case the maximum voltage is equal 

 to double the normal value, while if R = 0, or negligible, thus 



resembling a short-circuit, the voltage is zero. With R = -l 



there is no reflected wave at all. If R > \-^ there is a partial 



reflection with reversal of current, while, if R < \l -^ there is a 



* C 



partial reflection with reversal of voltage. With an inductive 

 receiving circuit, this acts in the first instant as a resistance of 

 infinite value, and voltage reaches double value, while a con- 

 denser under similar conditions would act as a short-circuit, and 

 the voltage would be zero. 



From the preceding it follows that when a dead high-tension 

 transmission line is to be energized the best practice to follow 

 would be to switch the line onto the dead transformers first by 

 means of the high-tension switch and then energize the com- 

 bination of line and transformers by closing the low-tension 

 switch to the generating source, this sequence of closing the 

 switches will obviate the high-tension surges and, consequently, 

 minimize the danger of insulation breakdown. 



It is also of greatest importance to consider the changes which 

 take place at a transition point between two circuits of different 

 characteristics, when a traveling wave passes from one to the 

 other, such as, for example, where an underground circuit joins an 

 overhead, or where a transmission line is connected to a trans- 

 former. 



Assume that a traveling wave with the voltage e and the cur- 

 rent i approaches from a circuit having a natural impedance 



Zi = <\j-l and enters a second circuit with a natural impedance of 



fr 2 



f tne wave wm * then be reflected and part 

 transmitted. It is also evident that at the transition point the 



