TC 9-64 _________________________________________________________________________
When the last capacitor is charged, the current from the source stops flowing
(view D).
3-94. Important facts to remember in the reflection of DC voltages in open-
ended lines are--
Voltage is reflected from an open end without change in polarity,
amplitude, or shape.
Current is reflected from an open end with opposite polarity and
without change in amplitude or shape.
Reflection of DC Voltage from a Short Circuit
3-95. A short-circuited line affects voltage change differently than the way an
open-circuited line affects it. The voltage across a perfect short circuit must
be zero; therefore, no power can be absorbed in the short, and the energy is
reflected toward the generator.
3-96. The initial circuit is shown in figure 3-25, view A. The initial voltage
and current waves (view B) are the same as those given for an infinite line. In
a short-circuited line the voltage change arrives at the last inductor in the
same manner as the waves on an open-ended line. In this case, however,
there is no capacitor to charge. The current through the final inductor
produces a voltage with the polarity shown in view C. When the field
collapses, the inductor acts as a battery and forces current through the
capacitor in the opposite direction, causing it to discharge (view D). Because
the amount of energy stored in the magnetic field is the same as that in the
capacitor, the capacitor discharges to zero.
3-97. Now there is no voltage to maintain the current through the next to the
last inductor. Therefore, this inductor discharges the next to the last
capacitor.
3-98. As each capacitor is discharged to zero, the next inductor effectively
becomes a new source of voltage. The amplitude of each of these voltages is
equal to E/2, but the polarity is the opposite of the battery at the input end of
the line. The collapsing field around each inductor, in turn, produces a
voltage that forces the current to continue flowing in the same direction,
adding to the current from the source to make it 2I. This action continues
until all the capacitors are discharged (view E).
3-99. Reflected waves from a short-circuited transmission line are
characterized as follows:
The reflected voltage has the opposite polarity but the same
amplitude as the incident wave.
The reflected current has the same polarity and the same amplitude
as the incident current.
3-30
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