4.11
Date Code 20170927 Instruction Manual SEL-751 Relay
Protection and Logic Functions
Group Settings (SET Command)
The line would typically use line impedance settings Z1MAG, Z1ANG,
Z0MAG, and Z0ANG in the fault locator and in automatically making direc-
tional element settings Z2F, Z2R, Z0F, and Z0R. Use a corresponding line
length setting (LL) in the fault locator.
If the protected line belongs to a hybrid power system, such as shown in
Figure 4.46, refer to Z0MTA—Zero-Sequence Maximum Torque Angle for
information on the Z0MTA setting.
On both hybrid and solidly grounded power systems, Z0ANG must be set to
the actual zero-sequence line angle to allow correct fault locator operation for
forward faults involving ground.
The line impedance settings Z1MAG, Z1ANG, Z0MAG, and Z0ANG are set
in secondary. Line impedance ( primary) is converted to secondary:
primary • (CTR/PTR) = secondary
where:
CTR = phase (IA, IB, IC) current transformer ratio
PTR = phase (VA, VB, VC) potential transformer ratio
Line length setting LL is unitless and corresponds to the line impedance set-
tings. For example, if a particular line length is 15 miles, enter the line imped-
ance values ( secondary) and then enter the corresponding line length:
LL = 15.00 (miles)
If this length of line is measured in kilometers rather than miles, then enter:
LL = 24.14 (kilometers)
Fault Location
The relay reports the fault location if the EFLOC setting := Y and the fault
locator operates successfully after an event report is generated. If the fault
locator does not operate successfully, $$$$$$ is listed in the field. Fault loca-
tion is based on the line impedance settings Z1MAG, Z1ANG, Z0MAG, and
Z0ANG; source impedance settings Z0SMAG and Z0SANG; and correspond-
ing line length setting LL. Because the fault locating function requires three-
phase voltages, the Group setting EFLOC cannot be set to Y when Group
setting VNOM := OFF. Similarly, the Group setting EFLOC is hidden and set
to N internally when the Group setting SINGLEV := Y or the relay is ordered
with no voltage inputs.
Overcurrent Elements
Four levels of instantaneous/definite-time elements are available for phase,
neutral, residual, and negative-sequence overcurrent as shown in Table 4.8
through Table 4.11 and in Figure 4.2.
Each element can be torque controlled through the use of appropriate
SEL
OGIC control equations (for example, when 50P1TC := IN401, the 50P1
element is operational only if IN401 is asserted).
NOTE: The relay does not require
line impedance settings when setting
SINGLEV= Y, and hides these settings
from the SET and SHO commands.
Table 4.7 Fault Locator Setting
Setting Prompt Setting Range
Setting Name :=
Factory De fault
FLT LOC ENABLE Y, N EFLOC := N
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