Siemens SIPROTEC 7SJ61, Руководство пользователя, Страница: 160 / 454

Functions
2.10 Intermittent Ground Fault Protection
SIPROTEC, 7SJ61, Manual
C53000-G1140-C210-1, Release date 02.2008
160
The pickup signals of these functions will still be logged immediately. A TRIP command of one of these pro-
tective functions will cause the buffered messages to be cleared since no connection exists between tripping
function and buffered message.
A fault event is cleared when the time
T-reset
has expired or the TRIP command
„IEF Trip“
has been
terminated.
Terminating a fault event for the intermittent ground fault protection thus is a special case. It is the time
T-
reset
that keeps the fault event opened and not the pickup.
2.10.2 Setting Notes
General
The protection function for intermittent ground faults can only take effect and is only accessible if the current to
be evaluated (
133
,
INTERM.EF
or
with Ignd
) was configured in address
with 3I0 with Ignd,sens.
.
If not required, this function is set to
Disabled
.
The function can be turned
ON
or
OFF
under address
3301 INTERM.EF
.
The pickup threshold (r.m.s. value) is set in address
3302 Iie>
. A rather sensitive setting is possible to
respond also to short ground faults since the pickup time shortens as the current in excess of the setting in-
creases. The setting range depends on the selection of the current to be evaluated at address
133
INTERM.EF
.
The pickup time can be prolonged at address
3303 T-det.ext.
. This pickup stabilization is especially impor-
tant for the coordination with existing analog or electromechanical overcurrent relays. The time
T-det.ext.
can also be disabled (
T-det.ext.
= 0).
The stabilized pickup starts the counter
T-sum det.
. This counter is stopped but not reset when the picked
up function drops out. Based on the last counter content the counter resumes counting when the stabilized
function picks up next. This sum of individual pickup times, which are to initiate tripping, is set at address
3304
T-sum det.
. It represents one of the four selectivity criteria (pickup value
Iie>
, detection extension time
T-
det.ext.
, counter
T-sum det.
and reset time
T-reset
) for coordinating the relays on adjacent feeders
and is comparable to the time grading of the time overcurrent protection. The relay in the radial network which
is closest to the intermittent fault and picks up, will have the shortest summation time
T-sum det.
.
Figure 2-55 Example of selectivity criteria of the intermittent ground fault protection
The reset time, after which the summation is reset in healthy operation and the protection resumes normal
status, is configured to
T-reset
at address
3305
.
Address
3306 Nos.det.
specifies the number of pickups after which a ground fault is considered intermittent.