31
Ｃｎ
Ｒｎ
Ｃ３
Ｃ２
Ｃ１
Ｒ３
Ｒ２
Ｒ１
Ｃ０
Ｒ０
6.7 Changes in the Current Flowing through an Insulator
In insulation resistance measure ments, a large amount of current flows
upon the application of the test voltage to the insulator. The current
gradually reduces its value with time, but it takes a time until the value
becomes stable and fixed. This phenomena is due to the combination of the
charg ing current, absorption current, and leakage current, and it is
generally called dielectric absorption phenomena. The equivalent circuit of
an insulator is considered as shown in Fig. 6.7.1.
Fig. 6.7.1
When a voltage is applied to the circuit, a charging current flows through a
bank of capacitors, C
0
, C
1
, C
2
,….C
n
. Firstly, C
0
is charged, and
other cap acitors follow. As the charging progresses the current throug h R
0
constantly flows as shown in Fig. 6.7.2.
Fig. 6.7.2
R
0
is an insulation resistance to be measured, but, C
0
, C
1
, C
2
,
….
C
n
０
Charge curr ent
Absorpti on current
Leakage current
Time
（Charge）
Volt age
appl ic at io n
Curr ent
（Dis charge）
Curr ent
short
