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Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
The values for the time delay settings T 3I0>>> (address 3112), T 3I0>> (address 3122) and T 3I0> (ad-
dress 3132) are derived from the earth fault grading coordination diagram of the system.
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".
The set time delays are pure additional delays, which do not include the operating time (measuring time).
Inverse time stage with IEC characteristic
If the fourth stage has been configured as an inverse time overcurrent stage with IEC characteristic (address
131 Earth Fault O/C = TOC IEC), you first set the mode: 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.
For the inverse time overcurrent stage 3I
variant and configuration (Section 2.1.1.3, address 131). With 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 (long inverse, 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 incorporated. 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 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 characteristic.
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".
236
it is possible to select different characteristics depending on order
0P
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
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