SEG Electronics GmbH
Manual MRG3
84
DOK-TD-MRG3, Rev. D
7.8.12 Inverse time over current protection relay
According to IEC 255-4 or BS 142
Normal Inverse (Type A)
𝑡 =
0.14
(
𝐼
𝐼
𝑆
)
0.02
− 1
∙ 𝑡
𝐼
> [𝑠]
Very Inverse (Type B)
𝑡 =
13.5
(
𝐼
𝐼
𝑆
) − 1
∙ 𝑡
𝐼
> [𝑠]
Extremely Inverse (Type C)
𝑡 =
80
(
𝐼
𝐼
𝑆
)
2
− 1
∙ 𝑡
𝐼
> [𝑠]
Long Time Inverse
𝑡 =
120
(
𝐼
𝐼
𝑆
) − 1
∙ 𝑡
𝐼
> [𝑠]
RI-Inverse Time
𝑡 =
1
0.339 −
0.236
(
𝐼
𝐼
𝑆
)
∙ 𝑡
𝐼
> [𝑠]
*RXIDG
– characteristic
𝑡 = (5.8 − 1.35 ∙ ℓ𝑛 (
𝐼
𝐼𝑠 ∙ 𝑡
𝐼>
)) [𝑠]
Where:
t
=
tripping time
t
I
>
=
time multiplier
I
=
fault current
Is
=
Starting current
ln
=
natural logarithm
*only for earth current
