3-22Figure 3-21.—Ac applied to an equivalent transmission line.In view B the generator voltage starts from zero (T1) and produces the voltage shown. As soon as asmall voltage change is produced, it starts its journey down the line while the generator continues toproduce new voltages along a sine curve. At T2 the generator voltage is 70 volts. The voltages still movealong the line until, at T3, the first small change arrives at point W, and the voltage at that point startsincreasing. At T5, the same voltage arrives at point X on the line. Finally, at T7, the first small changearrives at the receiving end of the line. Meanwhile, all the changes in the sine wave produced by thegenerator pass each point in turn. The amount of time required for the changes to travel the length of theline is the same as that required for a dc voltage to travel the same distance.At T7, the voltage at the various points on the line is as follows:At the generator:-100 VAt point W:0 VAt point X:+100 VAt point Y:0 VIf these voltages are plotted along the length of the line, the resulting curve is like the one shown infigure 3-22, view A. Note that such a curve of instantaneous voltages resembles a sine wave. The changesin voltage that occur between T7 and T8 are as follows: