4.1.5.2
Function block
67/51N
PICKUP
TRIP
BLOCK
ENA_MULT
RCA_CTL
67/50N-2
PICKUP
TRIP
BLOCK
ENA_MULT
RCA_CTL
67/50N-1
PICKUP
TRIP
BLOCK
ENA_MULT
RCA_CTL
V0/VG/V2
V0/VG/V2
V0/VG/V2
I0/IG/I2
I0/IG/I2
I0/IG/I2
A070433-ANSI V1 EN
Figure 80:
Function block
4.1.5.3
Functionality
The earth-fault function 67/51N and 67/50N is used as directional earth-fault protection.
There are three different polarization signals - measured zero sequence voltage, calculated
zero sequence voltage and negative sequence voltage. The function picks up and trips
when the zero sequence current (I
0
) and zero sequence voltage (-V
0
) exceed the set limits
and the angle between them is inside the set operating sector. The function also picks up
and trips when the negative sequence current (I
2
) and negative sequence voltage (-V
2
)
exceed the set limits and the angle between them is inside the set operating sector. The trip
time characteristic for low stage (67/51N) and high stage (67/50N-1 and 67/50N-2) can be
selected to be either definite time (DT) or inverse definite minimum time (IDMT).
In the DT mode, the function trips after a predefined trip time and resets when the fault
current disappears. The IDMT mode provides current-dependent timer characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
timers or the function itself, if desired.
4.1.5.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are “Enable” and “Disable”.
The operation of 67/51N and 67/50N can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Section 4
1MRS240050-IB C
Protection functions
172
REF615R
Technical Manual
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