ABB Relion REG670, Applications Manual

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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
Phase-
ground
voltages
IN
UN
IEC13000013-1-en.vsd
IEC13000013 V1 EN
Figure 189: 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.
9.6.3 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.
In a high impedance system the fault current is assumed to be limited by the system
zero sequence shunt impedance to earth and the fault resistance only. All the series
impedances in the system are assumed to be zero.
Section 9
1MRK 502 071-UEN -
Current protection
358 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual