ABB RED615 Technical Manual page 312

Section 4
Protection functions
306
earth faults. The "Intermittent EF" mode is dedicated for detecting intermittent
earth faults in cable networks.
Traditional earth fault protection should always be used in parallel
with the INTRPTEF function.
The Fault indication logic module determines the direction of the fault. 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, the Timer 1 is activated from the first detected
transient. 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 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.
In the "Intermittent EF" mode the OPERATE output is activated when the
following conditions are fulfilled:
• the number of transients that have been detected exceeds the Peak counter
limit setting
• the timer has reached the time set with the Operate delay time
• and one additional transient is detected during the drop-off cycle
The timer calculates the start duration value START_DUR which indicates the
percentage ratio of the start situation and the set operating time. The value is
available in the monitored data view.
Timer 2
If the function is used in the directional mode and an opposite direction transient is
detected, the BLK_EF output is activated for the fixed delay time of 25 ms. If the
START output is activated when the BLK_EF output is active, the BLK_EF output
is deactivated.
1YHT530004D05 D
615 series
Technical Manual