Directional Functions; Non-Directional Earth Fault Current Protection; Residual Overvoltage Release And Protection - ABB REC650 Technical Manual

Section 6
Current protection
6.5.7.5
6.5.7.6
6.5.7.7
118

Directional functions

For all the directional functions there are directional start signals STFW: fault in the
forward direction, and STRV: start in the reverse direction. Even if the directional
function is set to operate for faults in the forward direction a fault in the reverse
direction will give the start signal STRV. Also if the directional function is set to
operate for faults in the reverse direction a fault in the forward direction will give the
start signal STFW.

Non-directional earth fault current protection

This function will measure the residual current without checking the phase angle. The
function will be used to detect cross-country faults. This function can serve as
alternative or back-up to distance protection with phase preference logic.
The non-directional function is using the calculated residual current, derived as sum
of the phase currents. This will give a better ability to detect cross-country faults with
high residual current, also when dedicated core balance CT for the sensitive earth fault
protection will saturate.
This sub-function has the possibility of choice between definite time delay and inverse
time delay. The inverse time delay shall be according to IEC 60255-3.
For trip, the residual current 3I
When the function is activated binary output signal STNDIN is activated. If the output
signal is active after the set delay tINNonDir or after the inverse time delay the binary
output signals TRIP and TRNDIN are activated.

Residual overvoltage release and protection

The directional function shall be released when the residual voltage gets higher than
a set level.
There shall also be a separate trip, with its own definite time delay, from this level set
voltage level.
For trip, the residual voltage 3U
Trip from this function can be blocked from the binary input BLKUN.
When the function is activated binary output signal STUN is activated. If the output
signals are active after the set delay tUNNonDir TRIP and TRUN are activated. A
simplified logical diagram of the total function is shown in figure 49.
shall be larger than the set level (INNonDir>).
0
shall be larger than the set level (UN>).
0
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