Seg HighTECH Line - Page 35

TD_MRI1_06.05_GB 35
7.3.7 Inverse time overcurrent protection relay
According to IEC 255-4 or BS 142
Normal Inverse
[]
t
I
Is
t
I
s=






−
>
014
002
1
,
,
Very Inverse
[]
t
I
Is
t
I
s=






−
>
135
1
,
Extremely Inverse
[]
t
I
Is
t
I
s=






−
>
80
2
1
Where: t = tripping time
t
I>
= time multiplier
I = fault current
Is = Starting current
7.3.8 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
7.3.9 Determination of earth fault direction (MRl1-ER/XR)
Measurement of active current
component for compensated
systems: I
E
x cos ϕ
Measurement of reactive
current component for isolated
systems: I
E
x sin ϕ
Angle measuring accuracy: ± 3° at I
E
x cos ϕ or I
E
x sin ϕ > 5 % I
E
7.3.10 Determination of earth fault direction (MRl1-SR)
Characteristic angle: "SOLI" setting - 110°
"RESI" setting - 170°
Effective angle: ± 70° related to relay characteristic angle at U
N
/ √3
Residual voltage sensitivity: <0.2 % U
N
at I = 0.1 x I
N