ABB RELION REX640 Technical Manual page 545

1MRS759142 C
REX640
Technical Manual
and should not be set too high as this can inhibit the disconnection of
the faulty feeder.
The residual current should be measured with an accurate CBCT to
minimize the measurement errors, especially phase displacement.
The parallel resistor should be kept connected during the healthy state
so that in case of a fault, earth-fault protection can immediately see
sufficient value of resistive component for operation. If the parallel
resistor is kept disconnected during the healthy state, it should be
immediately connected when the earth fault is detected. This enables
the earth-fault protection to operate without delay.
Transient detector
The Transient detector module is used for detecting transients in the residual current
and zero-sequence voltage signals. Whenever a transient is detected, this is indicated
with the PEAK_IND output. When the number of detected transients equals or
exceeds the Peak counter limit setting (without the function being reset, depending on
the drop-off time set with the Reset delay time setting), INTR_EF output is activated.
This indicates detection of a restriking or intermittent earth fault in the network.
Transient detector affects the operation of MFADPSDE (START and OPERATE
outputs) when operation mode is "Intermittent EF". For other operation modes,
("General EF", "Alarming EF"), PEAK_IND and INTR_EF outputs can be used for
monitoring purposes. The operation of Transient detector is illustrated in
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.
Transient detector is a non-directional function. Thus, if detection of
restriking or intermittent earth faults is wanted only in the faulted
feeder, the START and INTR_EF outputs must be ANDed in the
configuration.
Section 4
Protection functions
Figure 294.
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