2 Functions
224
7SD5 Manual
C53000-G1176-C169-1
Figure 2-98 Characteristic settings of the zero-sequence voltage time dependent stage —
without additional 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 operate. 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 di-
rection.
The time setting Add.T-DELAY (address 3147) allows an additional power-indepen-
dent delay time to be set.
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