7.6.2
Functionality
Negative sequence based overcurrent function DNSPTOC is typically used as
sensitive earth-fault protection of power lines, where incorrect zero sequence
polarization may result from mutual induction between two or more parallel lines.
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. Both steps are
provided with a settable definite time delay.
DNSPTOC protects against all unbalanced faults including phase-to-phase faults. The
minimum start current of the function must be set to above the normal system
unbalance level in order to avoid unwanted operation.
7.6.3
Function block
DNSPTOC
I3P*
U3P*
BLOCK
BLKOC1
ENMLTOC1
BLKOC2
ENMLTOC2
TRIP
TROC1
TROC2
START
STOC1
STOC2
DIROC1
DIROC2
CURRENT
VOLTAGE
UIANGLE
IEC09000125-1-en.vsd
IEC09000125 V1 EN
Figure 53:
DNSPTOC function block
7.6.4
Signals
Table 61:
DNSPTOC Input signals
Name
Type
Default
Description
I3P
GROUP
SIGNAL
-
Three phase group signal for current inputs
U3P
GROUP
SIGNAL
-
Three phase group signal for voltage inputs
BLOCK
BOOLEAN
0
Block of function
BLKOC1
BOOLEAN
0
Block of over current function OC1
ENMLTOC1
BOOLEAN
0
Enable signal for current multiplier - step1 (OC1)
BLKOC2
BOOLEAN
0
Block of over current function OC2
ENMLTOC2
BOOLEAN
0
Enable signal for current multiplier - step 2 (OC2)
1MRK 505 288-UEN A
Section 7
Current protection
123
Technical manual
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