When a required number of intermittent earth-fault transients set with the
Peak
counter limit
setting are detected without the function being reset (depends on
the drop-off time set with the
Reset delay time
setting), the START output is
activated. The INTR_EF output is activated to indicate the fault type is intermittent
or restriking earth fault. The operate timer is kept activated as long as transients
occur during the drop-off time defined by setting
Reset delay time
.
The OPERATE output is activated when
Operate delay time
has elapsed, required
number of transients has been detected, earth fault is detected by the GFC,
fault direction matches the
Directional mode
setting and estimated stabilized
fundamental frequency residual current exceeds set
Minimum operate current
setting.
The
Reset delay time
starts to elapse from each detected transient. Function
is reset if time between current peaks is more that
Reset delay time
or if the
General Fault Criterion release is reset. After OPERATE output activation, START and
OPERATE outputs are reset immediately at the falling edge of General Fault Criterion
release, that is, when zero-sequence voltage falls below
Voltage start value
. This
should be considered if “Intermittent EF" mode is applied in case earth faults are
only alarmed to avoid repetitive start and operate events.
To keep the operate timer activated between current spikes during
intermittent or restriking earth fault,
Reset delay time
should be set to a
value exceeding the maximum expected time interval between (obtained
at full resonance condition). The recommended value is at least 300 ms.
1MRS758755 C Protection functions
REC615 & RER615
Technical Manual
403
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