2.7 Earth fault overcurrent protection in earthed systems (optional)
157
7SA522 Manual
C53000-G1176-C155-3
Figure 2-66 Directional zero-sequence voltage time protection with non-directional backup stage
Zero Sequence
Power Protection
The zero sequence power protection operates according to a power-dependent trip
time characteristic. It can be used instead of an inverse time overcurrent stage.
The power is calculated from the zero sequence voltage and the zero sequence cur-
rent. The component S
r
is decisive in direction of a configurable compensation angle
Ï•
comp
, which is also referred to as compensated zero sequence power i.e.,
S
r
= 3 I
0
· 3 U
0
· cos (ϕ – ϕ
comp
)
where ϕ = ∠(U
0
; I
0
). Ï•
comp
thus determines the direction of the maximum sensitivity
(cos (ϕ – ϕ
comp
) = 1, if Ï• = Ï•
comp
). Due to its sign information the power calculation au-
tomatically includes the direction. The power for the reverse direction can be deter-
mined by reversing the sign.
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