ABB RELION REX640 Technical Manual page 484

Protection functions
fundamental frequency current. This setting should be set based on the value of
the parallel resistor of the coil, with security margin. For example, if the resistive
current of the parallel resistor is 10 A, then a value of 0.7×10 A = 7 A could be used.
The same setting is also applicable in case the coil is disconnected and the network
becomes unearthed. Generally, a smaller value should be used and it must never
exceed the value of the parallel resistor in order to allow operation of the faulted
feeder.
Fault indication logic
Depending on the set
detecting earth faults. The "Transient EF" mode is intended to detect all kinds of
earth faults. The "Intermittent EF" mode is dedicated for detecting intermittent
earth faults in cable networks.
The Fault indication logic module determines the direction of the fault. The
fault direction determination is secured by multi-frequency neutral admittance
measurement and special filtering techniques. This enables fault direction
determination which is not sensitive to disturbances in measured Io and Uo signals,
for example, switching transients.
When
the fault is in the protected feeder. When
used, the protection operates when the fault is outside the protected feeder
(in the background network). If the direction has no importance, the value "Non-
directional" can be selected. The detected fault direction (FAULT_DIR) is available in
the monitored data view.
In the "Transient EF" mode, when the start transient of the fault is detected and
the Uo level exceeds the set
kept activated until the Uo level exceeds the set value or in case of a drop-off, the
drop-off duration is shorter than the set
In the "Intermittent EF" mode, when the start transient of the fault is detected and
the Uo level exceeds the set
required number of intermittent earth-fault transients set with the
limit setting are detected without the function being reset (depends on the drop-
off time set with the
Timer 1 is kept activated as long as transients are occurring during the drop-off
time defined by setting
Timer 1
The time characteristic is according to DT.
In the "Transient EF" mode, the OPERATE output is activated after
time if the residual voltage exceeds the set "Voltage start value" . The Reset delay
time starts to elapse when residual voltage falls below Voltage start value . If there is
no OPERATE activation, for example, the fault disappears momentarily, START stays
activated until the the
and OPERATE signals are reset as soon as Uo falls below
484
Operation mode , INTRPTEF has two independent modes for
To satisfy the sensitivity requirements, basic earth-fault protection
(based on fundamental frequency phasors) should always be used in
parallel with the INTRPTEF function.
Directional mode setting "Forward" is used, the protection operates when
Reset delay time setting), the START output is activated. The
Reset delay time .
Reset delay time elapses. After OPERATE activation, START
Directional mode setting "Reverse" is
"Voltage start value" , Timer 1 is activated. Timer 1 is
Reset delay time .
Voltage start value , the Timer 1 is activated. When a
1MRS759142 F
Peak counter
Operate delay
Voltage start value .
REX640
Technical Manual