ABB Relion 670 Series Technical Reference Manual page 442

Section 7
Current protection
7.6
7.6.1
436
Sensitive directional residual overcurrent and power
protection SDEPSDE (67N)
Function description
Sensitive directional residual over
current and power protection
Introduction
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 · 3V
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 ground via the
capacitances between the phase conductors and ground, 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 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.
IEC 61850
identification
SDEPSDE
), compensated with a characteristic angle. Alternatively, the
0
level with a check of angle 3I
0
· cos φ, where φ is the angle between the residual current
0
1MRK505222-UUS C
IEC 60617 ANSI/IEEE C37.2
identification device number
- 67N
and cos φ.
0
Technical reference manual