9.6.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Sensitive directional residual over
current and power protection
SDEPSDE - 67N
9.6.2 Application
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
0
· cos φ, where φ is the angle between the residual current and the
residual voltage (-3V
0
), compensated with a characteristic angle. Alternatively, the
function can be set to strict 3I
0
level with a check of angle φ.
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
0
· 3V
0
· cos φ, where φ is the angle between the residual 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
0
). The characteristic angle is 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.
1MRK 506 369-UUS - Section 9
Current protection
Line distance protection REL670 2.2 ANSI 529
Application manual
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