ABB 615 series Technical Manual page 369

1MAC059074-MB A
615 series ANSI
Technical Manual
To satisfy the sensitivity requirements, basic ground-fault protection
(based on fundamental frequency phasors) should always be used in
parallel with the 67NIEF 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 IG and VG 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 VG
level exceeds the set Voltage start value, Timer 1 is activated. Timer 1 is kept activated
until the VG 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 VG
level exceeds the set Voltage pickup value, the Timer 1 is activated. When a required
number of intermittent ground-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 PICKUP 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 TRIP output is activated after Trip delay time if the
residual voltage exceeds the set Voltage pickup value. The Reset delay time starts to elapse
when residual voltage falls below Voltage pickup value. If there is no TRIP activation, for
example, the fault disappears momentarily, PICKUP stays activated until the the Reset
delay time elapses. After TRIP activation, PICKUP and TRIP signals are reset as soon as
VG falls below Voltage pickup value.
Section 4
Protection functions
363