ABB Relion REQ650, Applications Manual

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The value of k = 0.98 or even k = 0.99 is recommended in generator low forward power
applications as the trip delay is normally quite long. This filtering will improve
accuracy of the power function.
6.15 Negative sequence based overcurrent function
DNSPTOC
6.15.1 Identification
Function description IEC 61850
identification
IEC 60617
identification
ANSI/IEEE C37.2
device number
Negative sequence based overcurrent
function
DNSPTOC
3I2>
IEC09000132 V2 EN
46
6.15.2 Application
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.
6.15.3 Setting guidelines
Below is an example of Negative sequence based overcurrent function (DNSPTOC)
used as a sensitive earth-fault protection for power lines. The following settings must
be done in order to ensure proper operation of the protection:
GlobalBaseSel : Selects the global base value group used by the function to define
( IBase ), ( UBase ) and ( SBase ).
Section 6
1MRK 505 291-UEN A
Current protection
152
Application manual