Table of Contents
Advertisement
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.
2.12.2
Setting Notes
General
The protection function for intermittent ground faults can only take effect and is only accessible if the current to
be evaluated was configured in address 133, INTERM.EF (with Ignd or with 3I0 or 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..
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.
Figure 2-76
Address 3306 Nos.det. specifies the number of pickups after which a ground fault is considered intermittent.
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A5, Release date 11.2012
Example of selectivity criteria of the intermittent ground fault protection
2.12 Intermittent Ground Fault Protection
Functions
211
Advertisement
Table of Contents
