Setting Guidelines - ABB REC670 Applications Manual

Section 8
Current protection
8.6.3
182
• Sensitive directional residual overcurrent protection gives possibility for better
sensitivity. The setting possibilities of this function are down to 0.25 % of
IBase, 1 A or 5 A. This sensitivity is in most cases sufficient in high
impedance network applications, if the measuring CT ratio is not too high.
• Sensitive directional residual power protection gives possibility to use inverse
time characteristics. This is applicable in large high impedance earthed
networks, with large capacitive earth fault currents. In such networks, the
active fault current would be small and by using sensitive directional residual
power protection, the operating quantity is elevated. Therefore, better
possibility to detect earth faults. In addition, in low impedance earthed
networks, the inverse time characteristic gives better time-selectivity in case of
high zero-resistive fault currents.
Phase
currents
IN
Phase-
ground
voltages
UN
IEC13000013 V1 EN-US
Figure 79: Connection of SDEPSDE to analog preprocessing function block
Overcurrent functionality uses true 3I0, i.e. sum of GRPxL1, GRPxL2 and
GRPxL3. For 3I0 to be calculated, connection is needed to all three phase inputs.
Directional and power functionality uses IN and UN. If a connection is made to
GRPxN this signal is used, else if connection is made to all inputs GRPxL1,
GRPxL2 and GRPxL3 the internally calculated sum of these inputs (3I0 and 3U0)
will be used.

Setting guidelines

The sensitive earth fault protection is intended to be used in high impedance
earthed systems, or in systems with resistive earthing where the neutral point
resistor gives an earth fault current larger than what normal high impedance gives
but smaller than the phase-to-phase short circuit current.
1MRK 511 401-UEN A
IEC13000013-1-en.vsd
SEMOD171961-4 v10
Bay control REC670 2.2 IEC
Application manual