Siemens siprotec 7SD5, Руководство пользователя

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2.8 Earth Fault Protection in Earthed Systems (optional)
213
7SD5 Manual
C53000-G1176-C169-1
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-con-
trolled stage has already expired (without directional check). In case the zero se-
quence 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 cur-
rent. 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
= 3 I
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 au-
tomatically includes the direction. The power for the reverse direction can be deter-
mined 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 direc-
tion by a factor k.
Figure 2-92 shows the logic diagram. The tripping time depends on the level of the
compensated zero sequence power S
r
as defined above. For meshed earthed
systems the zero sequence voltage and the zero sequence current increase towards
the earth fault location. The inverse characteristic results in the shortest command
time for the relay closest to the fault. The other relays then reset.
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