
9
terminal temperature
-
10
℃
~
+
50
℃
relative humility
20-90%RH
2.7 Dimension: 275×220
×
160mm
3
2.8 Weigh: 1.8kg
Ⅲ
. Low Voltage Impulse Testing Method
1. Principle of Testing
The principle of cable fault testing is based on the asymmetrical
resistance’s reverse on the communication of the electric wave in
the cable.
Based on the theory of Transportation Line, every line has a unique
resistance Z
c,
which is depending on the structure of the circuit but
not the length of the line. In the symmetrical transportation line, the
resistance input equals the unique resistance at any point. If the
load of terminal equals the unique resistance, the current wave and
voltage wave on the transportation reverse none but absorbed
totally by the terminal. When the resistance at any point is unequal
to Z
c,
the electric wave reverse all or partly. The scale of reverse
polarity can be expressed by parameter P, the relation is on the
below:
Z
c
is the resistance of the transportation line
Z
o
is the resistance of the reverse transportation line
P
=
U
r
(
reflection wave
)
U
i
(
incident wave
)
=
Z
o
-
Z
c
Z
o
+
Z
c
(
1
)