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11.14
SEL-400 Series Relays
Instruction Manual
Date Code 20171006
Time and Date Management
Time-Synchronized Events
Use the power flow solution to verify the instantaneous positive-sequence imped-
ances of your system transmission lines.
State Estimation Verification
Electric utility control centers have used state estimation to monitor the state of
the power system for the past 20 years. The state estimator calculates the state of
the power system using measurements such as complex power, voltage magni-
tudes, and current magnitudes received from different substations. State estima-
tion uses an iterative, nonlinear estimation technique. The state of the power
system is the set of all positive-sequence voltage phasors in the network. Typi-
cally, several seconds or minutes elapse from the time of the first measurement to
the time of the first estimation. Therefore, state estimation is a steady-state repre-
sentation of the power system.
Consider using precise simultaneous positive-sequence voltage measurements
from the power system to verify your state estimation model. Take time-synchro-
nized high-resolution positive-sequence voltage measurements at all substations.
Send the relay synchrophasor messages to a central database to determine the
power system state.
Power system contingency analysis models rely on state-estimation techniques,
and may have inaccuracies caused by incorrect present-state information, or
errors in system characteristics, such as incorrect line and source impedance esti-
mates. The simultaneous event-report triggering technique described earlier in
this section can be used to verify present models.
NOTE:
Not all SEL-400 series relays
support synchrophasors.
With SEL-400 series relays acting as phasor measurement units (PMUs) installed
in several substations, synchrophasor measurements can be transmitted to a cen-
tral processor in near-real time, providing very accurate snapshots of the power
system. This type of data processing system provides system-state measurements
that are a few seconds old, rather than state estimates that may be several minutes
old. In addition, the synchrophasor results are real measurements, rather than
estimates.
for information on the PMU settings and the
communications protocols available for synchrophasor data collection.
Figure 11.8
Power Flow Solution
P = 154.1 MW
Q = 138.2 MVAR
P = 153.1 MW
Q = 147.8 MVAR
P = 153.7 MW
Q = 145.9 MVAR
P = 152.8 MW
Q = 140.5 MVAR
P = 306.5 MW
Q = 5.4 MVAR
Line Loss
P = 0.4 MW
Q = 7.7 MVAR
Line Loss
P = 0.3 MW
Q = 7.3 MVAR
S
T
R
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