3-64. In this illustration the conventional lines of force represent the electric

fields. For simplicity, the magnetic fields are not shown. Points of charge are

indicated by plus (+) and minus (-) signs, the larger signs indicating points of

higher amplitude of both voltage and current. Short arrows indicate direction

of current (electron flow). The waveform drawn below the transmission line

represents the voltage (E) and current (I) waves. The line is assumed to be

infinite in length so there is no reflection. Thus, traveling sinusoidal voltage

and current waves continually travel in phase from the generator toward the

load, or far end of the line. Waves traveling from the generator to the load are

called incident waves. Waves traveling from the load back to the generator

are called reflected waves and are explained later in this chapter.

3-65. Figure 3-20 shows a battery connected to a circuit that is the equivalent

of a transmission line. In this line, the series resistance and shunt

conductance are not shown. Also, in the discussion that follows, the line is

considered to have no losses.

3-66. As the switch shown in figure 3-20 is closed, the battery voltage is

applied to the input terminals of the line. Now, C1 has no charge and

appears, effectively, as a short circuit across points A and B. The full battery

voltage appears across inductor L1. Inductor L1 opposes the change of

current (0 now) and limits the rate of charge of C1.

3-67. Capacitor C2 cannot begin to charge until after C1 has charged. No

current can flow beyond points A and B until C1 has acquired some charge.

As the voltage across C1 increases, current through L2 and C2 charges C2.

This action continues down the line and charges each capacitor, in turn, to

the battery voltage. Thus, a voltage wave is traveling along the line. Beyond

the wavefront, the line is uncharged. Because the line is infinitely long, there

will always be more capacitors to be charged, and current will not stop

flowing. Thus, current will flow indefinitely in the line.

3-68. Notice that current flows to charge the capacitors along the line. The

flow of current is not advanced along the line until a voltage is developed

across each preceding capacitor. In this manner voltage and current move

down the line together in phase.

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