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
