7.6.2 Functionality
Negative sequence based overcurrent function (DNSPTOC, 46) may be used in power
line applications where the reverse zero sequence source is weak or open, the forward
source impedance is strong and it is desired to detect forward ground faults.
Additionally, it is applied in applications on cables, where zero sequence impedance
depends on the fault current return paths, but the cable negative sequence impedance is
practically constant.
The directional function is current and voltage polarized. The function can be set to
forward, reverse or non-directional independently for each step.
DNSPTOC (46) protects against all unbalanced faults including phase-to-phase faults.
The minimum pickup current of the function must be set to above the normal system
unbalance level in order to avoid unwanted tripping.
7.6.3 Function block
ANSI09000125-1-en.vsd
DNSPTOC (46)
I3P*
V3P*
BLOCK
BLKOC1
ENMLTOC1
BLKOC2
ENMLTOC2
TRIP
TROC1
TROC2
BFI_3P
PU_OC1
PU_OC2
DIROC1
DIROC2
CURRENT
VOLTAGE
VIANGLE
ANSI09000125 V1 EN
Figure 49: DNSPTOC (46) function block
7.6.4 Signals
Table 59: DNSPTOC (46) Input signals
Name
Type Default Description
I3P GROUP
SIGNAL
- Three phase group signal for current inputs
V3P GROUP
SIGNAL
- Three phase group signal for voltage inputs
BLOCK BOOLEAN 0 Block of function
BLKOC1 BOOLEAN 0 Block of over current function OC1
Table continues on next page
Section 7 1MRK 505 277-UUS C
Current protection
118
Technical Manual
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