ABB RELION Series Technical Manual page 395

1MRS758755 A
REC615 and RER615
Technical Manual
Operation mode "Intermittent EF" is dedicated for detecting restriking or intermittent
earth faults. A required number of intermittent earth fault transients set with the Peak
counter limit setting must be detected for operation. Therefore, transient faults or
permanent faults with only initial fault ignition transient are not detected in
"Intermittent EF" 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 Directional mode setting
• Estimated stabilized fundamental frequency residual current exceeds the set Min
operate current level
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.
Section 4
Protection functions
389