Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
224
A further time stage T rev. (U0inv) provokes non-directional tripping with a voltage-independent delay.
This stage can be set above the directional stage. When tripping with this stage it is, however, a prerequisite
that the time of the voltage-controlled stage has already expired (without directional check). In case the zero-
sequence voltage is too low or the voltage transformer circuit breaker is tripped, this stage is also disabled.
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 current. The component S
r
is
decisive in direction of a configurable compensation angle ϕ
comp
, which is also referred to as compensated
zero-sequence power, i.e.
S
r
= 3I
0
· 3U
0
· cos(ϕ – ϕ
Comp
)
where ϕ = ∠ (U
0
; I
0
). ϕ
Comp
thus determines the direction of the maximum sensitivity (cos(ϕ – ϕ
Comp
)=1 if
ϕ = ϕ
Comp
). Due to its sign information the power calculation automatically includes the direction. The power for
the reverse direction can be determined by reversing the sign.
The power-time characteristic can be displaced in power direction via a reference value S
ref
(= basic value for
the inverse characteristic for ϕ = ϕ
comp
) and in time direction by a factor k.
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