Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

Page: 166 / 824

4.60
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
The traditional application of this scheme provides accelerated (0.25 second)
Zone 2 tripping in the event of an undervoltage condition occurring during the
loss-of-field. To achieve this accelerated tripping, it is necessary to use a SEL
OGIC
control equation variable and a positive-sequence undervoltage element, 27V1X1.
The undervoltage element is generally set to 80 percent of the nominal voltage
for single-machine buses and 87 percent for multimachine buses.
Use any SEL
OGIC
control equation variable to define a tripping condition for
Zone 2 with undervoltage:
SV15 := 27V1X1 AND 40Z2
SV15PU := 0.25 seconds
SV15DO := 0.00 seconds
The Relay Word bit, SV15T, should be added to the SV08 SEL
OGIC
control
equation, along with the Zone 1 and Zone 2 conditions discussed previously,
to cause generator breaker and field breaker tripping (see Trip/Close Logic
Settings for details).
Figure 4.32 Loss-of-Field Element Operating Characteristic,
Negative Zone 2 Offset
Set 27V1X1P
0.8 * VNOM_X * 1000
1.732 * PTRX
--------------------------------------------------------- =
40Z1P = 1.0 pu