ABB RELION REX640 Technical Manual page 573

1MRS759142 F
Operation mode "Intermittent EF" is used to detect restriking or intermittent earth
faults. A required number of intermittent earth fault transients set with the
counter limit setting must be detected for operation. Therefore, transient faults
or permanent faults with only initial fault ignition transient are not detected in
this mode. The application of "Intermittent EF" mode is limited to low ohmic
intermittent or restriking earth faults.
In the "Intermittent EF" mode, the operate timer is started when the following
conditions are met.
• Transient is detected by the Transient detector (indicated with PEAK_IND
output)
• Earth fault is detected by the GFC at time of transient
• Fault direction equals
•
Estimated stabilized fundamental frequency residual current
set
supervision, and which is further defined with setting
(available options are "Adaptive", "Amplitude" and "Resistive").
When a required number of intermittent earth-fault transients set with the
counter limit setting are detected without the function being reset (depends on
the drop-off time set with the
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
The OPERATE output is activated when
number of transients has been detected, earth fault is detected by the GFC,
fault direction matches the
fundamental frequency residual current exceeds set
setting.
Reset delay time starts to elapse from each detected transient. Function is reset if
time between current peaks is more that
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
considered if "Intermittent EF" mode is applied in case earth faults are only alarmed
to avoid repetitive start and operate events.
REX640
Technical Manual
Directional mode setting
Min operate current level, which is applied in current magnitude threshold
Directional mode setting and estimated stabilized
Peak counter limit setting should not be set below 3 in order to provide
secure indication of intermittent/restriking earth faults. This is due to
the fact that sometimes the fault ignition transient is characterized
by highly distorted waveform, which may result in multiple transient
detection at time of fault ignition. By increasing the value of
limit setting, the security of correct fault type identification is increased.
To keep the operate timer activated between current spikes during
intermittent or restriking earth faults,
set above the maximum expected time interval between fault spikes
(obtained at full resonance condition). The recommended value is at least
300 ms.
Reset delay time setting), the START output is
Reset delay time .
Operate delay time has elapsed, required
Reset delay time or if the General Fault
Voltage start value . This should be
Reset delay time should be
Protection functions
1
I
exceeds the
o stab
Operating quantity
Minimum operate current
Peak counter
Peak
Peak
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