Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
236
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 3
I
0P
it is possible to select different characteristics depending on order
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“.
