Functionality - ABB RES670 Technical Manual

1MRK 511 408-UUS A
8.4.2
Phasor measurement unit RES670 2.2 ANSI
Technical manual

Functionality

In networks with high impedance grounding, the phase-to-ground fault current is
significantly smaller than the short circuit currents. Another difficulty for ground fault
protection is that the magnitude of the phase-to-ground fault current is almost
independent of the fault location in the network.
Directional residual current can be used to detect and give selective trip of phase-to-
ground faults in high impedance grounded networks. The protection uses the residual
current component 3I · cos φ, where φ is the angle between the residual current and
0
the residual voltage (-3V
function can be set to strict 3I
Directional residual power can also be used to detect and give selective trip of phase-
to-ground faults in high impedance grounded networks. The protection uses the
residual power component 3I
current and the reference residual voltage, compensated with a characteristic angle.
A normal non-directional residual current function can also be used with definite or
inverse time delay.
A backup neutral point voltage function is also available for non-directional residual
overvoltage protection.
In an isolated network, that is, the network is only coupled to ground via the
capacitances between the phase conductors and ground, the residual current always has
-90º phase shift compared to the residual voltage (3V
chosen to -90º in such a network.
In resistance grounded networks or in Petersen coil grounded, with a parallel resistor,
the active residual current component (in phase with the residual voltage) should be
used for the ground fault detection. In such networks, the characteristic angle is chosen
to 0º.
As the magnitude of the residual current is independent of the fault location, the
selectivity of the ground fault protection is achieved by time selectivity.
When should the sensitive directional residual overcurrent protection be used and when
should the sensitive directional residual power protection be used? Consider the
following:
• 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 grounded networks,
), compensated with a characteristic angle. Alternatively, the
0
level with a check of angle φ.
0
· 3V · cos φ, where φ is the angle between the residual
0 0
Section 8
Current protection
). The characteristic angle is
0
SEMOD171959-4 v12
229