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Two independent elements ZOV1 and ZOV2 are provided. The ZOV1 element is programmable
for definite time delayed or inverse time delayed (IDMT) operation, and the ZOV2 element for
definite time delayed operation only.
The inverse time characteristic is defined by equation (3).
⎡
⎤
⎢
1
⎥
=
×
t
TMS
( )
⎢
⎥
−
⎢
V
⎥
0
1
⎣
⎦
Vs
where:
t = operating time for constant voltage V
V
= Zero sequence voltage (V),
0
Vs = Zero sequence overvoltage setting (V),
TMS = time multiplier setting.
The IDMT characteristic is illustrated in Figure 2.2.11.
(3)
(seconds),
0
ZOV Overvoltage
Inverse Time Curves
1000.000
100.000
10.000
1.000
0.100
0.010
0
5
Applied Voltage (x Vs)
Figure 2.2.11
IDMT Characteristic of ZOV
⎯
⎯
83
TMS = 10
TMS = 5
TMS = 2
TMS = 1
10
15
20
6 F 2 S 0 8 4 2
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