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
= 3I
0
· 3U
0
· cos(ϕ – ϕ
Comp
)
The angle Ï•
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 Ï• = Ï•
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.
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