4.39
Date Code 20170814
Instruction Manual
SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
NOTE:
Most generators produce
enough third-harmonic voltage for
proper application of the 64G2
element; however, some generators
(for example, those with 2/3 pitch
winding) may not. In those cases, the
element based on the third-harmonic
voltage, such as the 64G2, cannot be
used for 100 percent Stator Ground
Protection.
When a ground fault occurs high in the winding of a resistance or high-
impedance grounded generator, a voltage appears at the generator neutral. The
neutral voltage magnitude during the fault is proportional to the fault location
within the winding. For instance, if a fault occurs 85 percent up the winding
from the neutral point, the neutral voltage is 85 percent of the generator rated
line-neutral voltage. The SEL-700G asserts the 64G1 Relay Word bit when
neutral voltage is greater than the 64G1P setting.
This function detects stator ground faults in all but the bottom 5 to 10 percent of the
generator winding. In this area close to the generator neutral, the neutral voltage
does not increase significantly during a generator ground fault. The SEL-700G uses
the third-harmonic voltage differential element to detect faults in this area.
The 64G2 third-harmonic voltage differential element measures the third-
harmonic voltage magnitudes at the generator terminals and neutral point,
then evaluates the equation:
If the difference between the measured third-harmonic voltage magnitudes is
greater than the 64G2P setting, the relay asserts the 64G2 Relay Word bit.
Figure 4.21 illustrates the 64G1 and 64G2 element operating characteristics.
Notice that while the 64G2 element detects faults near the neutral and
generator terminals, it has a dead band near the middle of the winding. The
width of this dead band is governed by the 64G2P setting and the amount of
third-harmonic voltage that the generator produces. The 64G1 element detects
generator winding faults in the 64G2 element dead band and vice versa.
Figure 4.21
64G Element Operating Characteristic
Typical generators produce varying amounts of third-harmonic voltage,
depending on machine construction and loading. The magnitudes of terminal
where
VP3 = measured generator terminal third-harmonic voltage
magnitude
64RAT = third-harmonic voltage ratio setting
VN3 = measured generator neutral third-harmonic voltage
magnitude
64G2P = differential sensitivity setting
NOTE:
The 64G third-harmonic
filters are cosine filters.
VP3
64RAT
VN3
–
64G2P
100%
0%
50%
Generator
Winding
Element Coverage
Areas
Grounding
Transformer
Dead Band
Dead Band
64G1
64G2
Содержание SEL-700G Series
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