TB XRI1-IR 02.00 E
29
8.3.4
Inverse time overcurrent protection relay
According to IEC 255-4 or BS 142
Normal Inverse (type A)
[ ]
t
I
Is
tI s
=
−
>
014
0 02
1
,
,
Very Inverse (type B)
[ ]
t
I
Is
tI s
=
−
>
135
1
,
Extremely Inverse (type C)
[ ]
t
I
Is
tI s
=
−
>
80
2
1
Where:
t = tripping time
t
I>
= time multiplier
I = fault current
Is = Starting current
8.3.5
Direction unit for phase overcurrent relay
Directional sensitivity for
voltage input circuit:
<0.025% U
N
(phase-to-phase voltage) at I = 1 x I
N
Connection angle:
90°
Characteristic angle:
15°, 27°, 38°, 49°, 61°, 72°, 83°
Effective angle:
±
78° related to relay characteristic angle at U
N
