ABB RELION REX640, Техническое руководство, Страница: 568 / 1960

The main task of the current magnitude supervision module is to secure
the correct directional determination of an earth fault so that only
the faulty feeder is disconnected or generates alarms. Therefore, the
threshold value
Min operate current should be selected carefully 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 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 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 the Transient detector is illustrated in Figure
327 .
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.
Protection functions 1MRS759142 F
568 REX640
Technical Manual