7.6
Sensitive directional residual overcurrent and power
protection SDEPSDE (67N)
Function description
IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Sensitive directional residual over
current and power protection
SDEPSDE
-
67N
7.6.1
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
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 3I
0
and cos 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 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.
Section 7
1MRK505222-UUS C
Current protection
436
Technical reference manual
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