Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
239
Figure 2-116
Characteristic settings of the zero-sequence voltage time-dependent stage — without addition-
al times
Zero-sequence power stage
If you have configured the fourth stage as zero-sequence power stage (address
131
Earth Fault O/C
=
Sr
inverse
), set the mode first: Address
3140
Op. mode 3I0p
. This stage can be set to operate
Forward
(usually towards line) or
Reverse
(usually towards busbar) or
Non-Directional
(in both directions). If the
stage is not required, set its mode to
Inactive
. The zero-sequence power protection is to operate always in
line direction.
Address
3141
3I0p PICKUP
indicates the minimum current value above which this stage is required to oper-
ate. The value must be exceeded by the minimum earth fault current value.
The zero-sequence power S
r
is calculated according to the formula:
S
r
= 3
I
0
· 3U
0
· cos(
ϕ
–
ϕ
Comp
)
The angle
ϕ
Comp
is set as maximum-sensitivity angle at address
3168
PHI comp
. It refers to the zero-sequence
voltage in relation to the zero-sequence current. The default setting 255° thus corresponds to a zero-sequence
impedance angle of 75° (255° – 180°). Refer also to margin heading „Zero-Sequence Power Protection“.
The trip time depends on the zero sequence power according to the following formula:
Where S
r
is the compensated power according to above formula. S
ref
is the setting value
S ref
(address
3156
), that indicates the pickup value of the stage at
ϕ
=
ϕ
comp
. Factor
k
(address
3155
) can be set to displace
the zero-sequence time characteristic in time direction, the reference value
S ref
can be set for displacement
in power direction.
The time setting
Add.T-DELAY
(address
3147
) allows an additional power-independent delay time to be set.