ABB REF615 Applications Manual page 162

Section 5
Protection functions
156
protection for feeder earth faults when it is applied to the trip feeders feeding the
busbar. In intermittent earth-fault situations, this may cause the back-up protection
to trip without the dedicated intermittent earth-fault protection function for the
corresponding feeder.
INTRPTEF can be used in parallel with non-directional and directional earth-fault
functions. The function can reliably detect whether the fault is in the forward or
reverse area when looking from the feeder's perspective. In case of a forward type
fault, that is, when the fed cable is faulty, a trip signal is sent to the circuit breaker.
In case of a reverse type fault, meaning that the fault is on some other feeders, the
BLK_EF output is activated for a fixed time of 25 ms. This signal can be used for
blocking the earth-fault functions to prevent erroneous trips when the function is set
to operate with "Intermittent EF" mode.
In the following example, an intermittent earth-fault situation is shown in a neutral
compensated network. The faulty feeder (feeder j) feeds the fault current to the fault
point. In the healthy feeder (feeder v), the fault current is also detected but the
direction is reverse.
INTRPTEF detects transients in the residual current and residual voltage signals in
forward direction in the feeder (j). The adjustable drop-off timer starts counting when
a transient is detected. When the number of transients occurring within the drop-off
time meets the set limit, the function starts and stays active until transients are no
longer detected. When the operate delay time has elapsed, INTRPTEF operates if it
detects the next successive transients and the counter value is correct. The function
sends a trip command to the circuit breaker regarding the faulty feeder accordingly.
The requirement that one additional transient is needed after the
operate delay time is exceeded can cause additional operate time
delays. However, this functionality is implemented to prevent
unwanted trips.
1MRS756378 D
REF615
Application Manual