11
situation, we need add amount of current or high voltage impulse to
discharge it and get the reverse wave by the short circuit in a wink
by flashover electric arch.
IV. High Voltage DC Flashover Method
When the resistance of fault is really high, before it forms a
constant current tunnnel, it can grandually rise the voltage on the
cable. Reaching some voltage, the fault point is first been sparked
over forming the flashover, and we can use the electric arch added
to the voltage to form a short circuit reverse. The reverse wave at
the input terminal forms the open reverse by the high resistance
resourse. So the voltage reverse many times between the input
terminal and output terminal until it runs out of energy. The grahp of
testing principlewave form of reverse wave are as below:
The distance of the fault point:
Among: T
＝
t
2
－
t
1
＝
t
2
－
t
1
＝
t
2
－
t
1
＝
……
T
P=1 off line
P=-1 short circuit
P=0 regular
V
A
R
3
R
2
R
1
D
device
Test line
Figure 2
L
x
＝
1
2
V·T
