ABB RELION REX640 Technical Manual page 453

1MRS759142 C
REX640
Technical Manual
To satisfy the sensitivity requirements, basic earth fault protection
(based on fundamental frequency phasors) should always be used in
parallel with the INTRPTEF function.
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 Directional mode setting "Forward" is used, the protection operates when the
fault is in the protected feeder. When Directional mode setting "Reverse" is 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 "Voltage start value", Timer 1 is activated. Timer 1 is 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 Reset delay time.
In the "Intermittent EF" mode, when the start transient of the fault is detected and the
Uo level exceeds the set Voltage start value, the Timer 1 is activated. 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 Timer 1 is kept activated
as long as transients are occurring during the drop-off time defined by setting Reset
delay time.
Timer 1
The time characteristic is according to DT.
In the "Transient EF" mode, the OPERATE output is activated after Operate delay 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 Reset delay time elapses. After OPERATE activation, START
and OPERATE signals are reset as soon as Uo falls below Voltage start value.
Section 4
Protection functions
447