4.43
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
This value should be greater than 15 percent for the most
dependable stator ground protection. The referenced
spreadsheet performs this calculation automatically.
NOTE:
Although the minimum low-
winding coverage usually occurs at no
load, this is not always the case. Verify
coverage at all loads for which VP3
and VN3 are available.
Step 9. Use the following equation to select the 64G1P setting to detect
faults in the top 95–98 percent of the generator winding:
The 64G1P setting must be greater than 0.5 V secondary. Zero-
sequence voltage can appear across the grounding transformer
secondary during a system ground fault resulting from
capacitive coupling between the windings of the unit
transformer. If 64G1P is less than the zero-sequence voltage,
then the 64G1D setting must be longer than system ground
fault clearing time to provide security.
Ensuring 64G2
Min
:= 15 percent, and selecting 64G1P for at
least 95 percent winding coverage, gives an overlap of 10
percent or greater between the elements.
Step 10. Select the 64G2D delay setting, keeping in mind that detection
of a single stator ground fault by this element may not require
immediate tripping. The element is only used on generators
where high grounding impedance limits the ground-fault current. At
minimum, the 64G2D setting must be greater than the time
necessary to clear faults on the transmission system. Faults and other
disturbances can affect the measured harmonic voltages.
Third-Harmonic Neutral Undervoltage Setting Recommendations
(Use With Open-delta Potentials and EXT3V0_X := NONE.).
The vast
majority of generator protection applications benefit from the improved
ground fault sensitivity that the previously described third-harmonic voltage
differential protection scheme offers. In the event that your protection
standards require third-harmonic neutral undervoltage protection, use the
following setting procedure to define the protection settings.
Typically, the minimum neutral third-harmonic voltage occurs at no-load
conditions. However, some cases have been observed where the minimum
voltage occurs with the machine partially loaded. Therefore, we recommend
64G2
M in
64RAT
64RAT
PTRX
PTRN
----------------
+
------------------------------------------
64G2P
64RAT
PTRX
PTRN
----------------
+
VP3_NL
VN3_NL
+
PTRN
PTRX
----------------
-------------------------------------------------------------------------------------------------------------------------------------
–
100
=
64G2
M in
_________%
=
where
kV = nominal machine line-to-line voltage, kV primary
PTRN = Ngt • Nat
Ngt = grounding transformer ratio to 1
Nat = auxiliary transformer ratio to 1, use 1 if relay VN
input is connected directly to the grounding
transformer secondary
64G1P
1
95%
100%
--------------
–
kV
1000
1.73
PTRN
--------------------------------
V secondary,
=
assuming 95 percent coverage
NOTE:
Perform the procedure when
the relay is first installed, but after
the generator being protected is
connected to its step-up transformer
or bus. Remove the 64G2T Relay
Word bit from the relay tripping
SEL
OGIC
control equation. Use
64G1P := 5 V during the test. Set the
balance of tripping functions
according to the requirements of the
particular generator. Leave these
tripping functions in service to
protect the generator in the event
that a fault occurs during the test
sequence.
Содержание SEL-700G Series
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