ABB RELION REX640 Technical Manual page 551

1MRS759142 C
REX640
Technical Manual
• Transient is detected by Transient detector (indicated with PEAK_IND output)
• Earth fault is detected by the GFC at the time of transient
• Fault direction equals Directional mode setting
•
Estimated stabilized fundamental frequency residual current
set Min operate current level, which is applied in current magnitude threshold
supervision, and which is further defined with setting Operating quantity
(available options are "Adaptive", "Amplitude" and "Resistive").
When a required number of intermittent earth-fault transients set with the Peak
counter limit setting are detected and the function is not 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.
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, the required
number of transients has been detected, earth fault is detected by the GFC, the fault
direction matches the Directional mode setting and the estimated stabilized
fundamental frequency residual current exceeds the set Min operate current setting.
Reset delay time starts to elapse for each detected transient. The function is reset if the
time between current peaks is more than Reset delay time or if the GFC release is reset.
After OPERATE output activation, START and OPERATE outputs are reset
immediately at the falling edge of the GFC release, that is, when zero-sequence
voltage falls below Voltage start value. This should be considered if "Intermittent EF"
mode is applied if earth faults are only alarmed to avoid repetitive start and operate
events.
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 Peak
counter 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, Reset delay time should be set
above the maximum expected time interval between fault spikes
(obtained at full resonance condition). The recommended value is at
least 300 ms.
Section 4
Protection functions
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