EF counter Lim
+1 detected transients). OPERATE output activation occurs always at
time of detected transient. OPERATE output signal has fixed length of 100 ms, but
OP_INTR_EF signal is activated for only one cycle time i.e. 2. 5m.
Several factors affect the magnitude and frequency of fault transients,
such as the fault inception angle on the voltage wave, fault location,
fault resistance and the parameters of the feeders and the supplying
transformers. If the fault is permanent (non-transient), the initial
fault transient in current and voltage can be measured, whereas the
intermittent fault creates repetitive transients. The practical sensitivity
of transient detection is limited to approximately a few hundreds
of ohms of fault resistance. Therefore, the application of transient
detection is limited to low-ohmic earth faults.
Setting
Intr EF counter Lim
minimum value is 3 in order to provide
secure indication of intermittent/re-striking earth fault. This is due to
the fact that sometimes the fault ignition transient is characterized by
highly distorted waveform, which may result into multiple transients to
be detected at time of fault ignition. By increasing the value of
Intr
EF counter Lim
setting, one increases the security of correct fault type
identification.
Information about detected intermittent earth fault is also available in
Recorded data
as
Intermittent EF Det
or in Output data as INTR_EF.
During re-striking/intermittent earth faults, the very high current
transient may result to very fast operation times in case operation
principle is based on earth fault current or touch voltage estimate.
In case longer and more deterministic operation during re-striking/
intermittent earth faults is preferred, the operation can be based on
counted number of transients instead of IDMT operation. In transient
counter-based operation the setting
Reset delay time
should be set to
low value, say 20-40 ms. For the Intermittent earth-fault module reset
delay time is defined with setting
Intr EF reset time
. During intermittent
earth faults, typically longer reset time is needed to prevent unwanted
function reset between the current spikes. Recommended setting value
for
Intr EF reset time
is between 300-500 ms.
Actual operation time of intermittent earth-fault module cannot pre-
determined exactly as the timing of successive transients is not
constant.
At time OPERATE output is activated from intermittent earth-fault
protection, also output OP_INTR_EF is activated OPERATE output signal
has fixed length of 100 ms, but OP_INTR_EF signal is activated for
only one cycle time i.e. 2.5 m. If OP_INTR_EF is to be used in e.g.
protection logics, it should be prolonged with TOF-function in protection
configuration.
Applicable settings for Intermittent earth-fault module are:
Ena Intermit EF mode,
Intr EF counter Lim, Intr EF operate time and Intr EF reset time
.
Note that setting
CB Delay Comp
(circuit breaker delay compensation) is not
applicable in definite time operation, but it must be taken into account in setting
Intr EF operate time
.
Protection functions
1MRS759142 F
632 REX640
Technical Manual
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