2.8 Earth Fault Protection in Earthed Systems (optional)
221
7SD5 Manual
C53000-G1176-C169-1
The set time delays are pure additional delays, which do not include the operating time
(measuring time).
Inverse Time Stage
with IEC Character-
istic
Also for the inverse time overcurrent stage the operating mode is initially set: address
3140 Op. mode 3I0p. The stage can be set to operate Forward (usually towards
line), Reverse (usually towards busbar) or Non-Directional (in both directions).
If the stage is not required, set its mode to Inactive.
For the inverse time overcurrent stage 3I
0P
it is possible to select from a variety of
characteristics depending on the version of the relay and the configuration (Section
2.1.1.3, address 131) that was selected. If an inverse overcurrent stage is not re-
quired, set address 131 Earth Fault O/C = Definite Time. The 3I
0P
stage can
then be used as a fourth definite time stage (refer to „Definite Time Stages“ above) or
deactivated. With the IEC characteristics (address 131 Earth Fault O/C = TOC
IEC) the following options are available in address 3151 IEC Curve:
Normal Inverse (inverse, type A according to IEC 60255–3),
Very Inverse (very inverse, type B according to IEC 60255–3),
Extremely Inv. (extremely inverse, type C according to IEC 60255–3), and
LongTimeInverse (longtime, type B according to IEC 60255–3).
The characteristics and equations they are based on are listed in the Technical Data.
The setting of the pickup threshold 3I0p PICKUP (address 3141) is similar to the
setting of definite time stages (see above). In this case it must be noted that a safety
margin between the pickup threshold and the set value has already been incorporat-
ed. Pickup only occurs at a current which is approximately 10 % above the set value.
The time multiplier setting 3I0p Time Dial (address 3143) is derived from the
grading coordination chart which was set up for earth faults in the system.
In addition to the inverse current dependant time delay, a constant (fixed length) time
delay can also be set if this is required. The setting Add.T-DELAY (address 3147) is
added to the time of the set curve.
During the selection of the current and time settings, regard must be taken as to
whether a stage should be direction dependent and whether it uses teleprotection.
Refer also to the margin headings „Determination of Direction“ and „Teleprotection
with Earth Fault Protection“.
Inverse Time Stage
with ANSI Charac-
teristic
Also for the inverse time overcurrent stage the operating mode is initially set: address
3140 Op. mode 3I0p. The stage can be set to operate Forward (usually towards
line), Reverse (usually towards busbar) or Non-Directional (in both directions).
If the stage is not required, set its mode to Inactive.
For the inverse time overcurrent stage 3I
0P
it is possible to select from a variety of
curves depending on the version of the relay and the configuration (Section 2.1.1,
address 131) that was selected. If an inverse overcurrent stage is not required, set
address 131 Earth Fault O/C = Definite Time. The 3I
0P
stage can then be
used as a fourth definite time stage (refer to „Definite Time Stages“ above). With the
ANSI characteristics (address 131 Earth Fault O/C = TOC ANSI) are available at
address 3152 ANSI Curve:
Inverse,
Short Inverse,
Long Inverse,
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