Sensitive Directional Residual Overcurrent And Power Protection Sdepsde; Identification; Application - ABB REQ650 Applications Manual

Section 6
Current protection
6.7
6.7.1
6.7.2
122
Sensitive directional residual overcurrent and power
protection SDEPSDE

Identification

Function description
Sensitive directional residual over
current and power protection

Application

In networks with high impedance earthing, the phase-to-earth fault current is
significantly smaller than the short circuit currents. Another difficulty for earth-fault
protection is that the magnitude of the phase-to-earth 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-
earth faults in high impedance earthed 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 (-3U
the function can be set to strict 3I
Directional residual power can also be used to detect and give selective trip of phase-
to-earth faults in high impedance earthed networks. The protection uses the residual
power component 3I · 3U
0
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 back-up neutral point voltage function is also available for non-directional sensitive
back-up protection.
In an isolated network, that is, the network is only coupled to earth via the capacitances
between the phase conductors and earth, the residual current always has -90º phase
shift compared to the reference residual voltage. The characteristic angle is chosen to
-90º in such a network.
In resistance earthed networks or in Petersen coil earthed, with a parallel resistor, the
active residual current component (in phase with the residual voltage) should be used
for the earth-fault detection. In such networks the characteristic angle is chosen to 0º.
As the amplitude of the residual current is independent of the fault location the
selectivity of the earth-fault protection is achieved by time selectivity.
IEC 61850
identification
SDEPSDE
), compensated with a characteristic angle. Alternatively,
0
level with a check of angle 3I
0
· cos φ, where φ is the angle between the residual current
0
1MRK 505 291-UEN A
IEC 60617 ANSI/IEEE C37.2
identification device number
- 67N
and cos φ.
0
Application manual