4.44
SEL-700G Relay
Instruction Manual
Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
measuring the neutral third-harmonic voltage at various real and reactive load
conditions to find the minimum voltage.
Step 1. Operate the generator at various loads. Use the SEL-700G
METER command and record the values of neutral third-
harmonic voltage.
VN3_min := VN3/PTRN = ______Minimum third harmonic
neutral voltage V secondary.
Step 2. Set the 64RAT setting equal to 0.0 to disable third-harmonic
voltage differential protection and enable third-harmonic
neutral undervoltage protection. The relay does this
automatically and hides the 64RAT setting if DELTAY_X := D.
64RAT := 0.0
Step 3. Set the 64G2P setting approximately 50 percent of the
generator minimum third-harmonic neutral voltage:
It is not possible to calculate the low-winding coverage this
setting offers, because the third-harmonic terminal voltages are
unavailable.
Step 4. 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 the 64G1P setting is less than the zero-sequence
voltage, then the 64G1D setting must be longer than system ground fault
clearing time to provide security.
100% Stator Ground Fault Tripping.
If your company practice is to trip
for stator ground fault, use the 100 percent stator ground fault elements to trip
the generator main breaker, the field breaker, the prime mover, and the
generator lockout relay (generator shutdown). If your company practice is to
alarm only for stator ground fault, use the 64G1T and 64G2T Relay Word bits
to control outputs for alarming to an operator. Default configuration of the
SEL-700G is to shut down the generator by Relay Word bits 64G1T and
64G2T. See Trip/Close Logic Settings for more detail.
where
kV = nominal machine line-to-line voltage, kV primary
PTRN = Ngt • Nat
Ngt = grounding transformer ratio to 1
Nat = neutral voltage auxiliary transformer ratio to 1, use 1
if relay VN input is connected directly to the
grounding transformer secondary
64G2P
0.5
VN3_min V secondary
=
64G2P
__________________ V secondary
=
64G1P
1
95%
100%
--------------
–
kV
1000
1.73
PTRN
--------------------------------
V secondary,
=
assuming 95 percent coverage
Содержание SEL-700G Series
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