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Gestionnairedu Rseau de Transport d'Electricit
2008 IEEE PES General Meeting: Panel on Best Practices in State Estimation
Experiences and practices on State Estimation in
RTE (French Transmission System Operator)
Patrick Panciatici (RTE), Yacine Hassaine (RTE)
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2008 IEEE PES General Meeting: Panel on Best Practices in State Estimation, 2
Presentation of SE in RTE
RTE operates the whole French transmission system : (400kV to 63kV, 2500
substations, 100300 km of circuits and 1150 transformers), 7 regional control
centers and 1 National
State Estimation provides input for all networks analysis
Measurements are received every 10 s.
An event is sent, when the status of a switching device changes.
Which kind of measurements ?Active and reactive power flows on branches,
Active and reactive powers on load and generators,
Voltage magnitudes in substation on busbars,
Internal substation current measurements and tap positions are not transmitted.
Coherent stateMeasurements, Topology
Electrical characteristics
State
Estimation
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Snapshot Generation : Consistency between topology and measurements
A new status may arrive before measurements affected by the switching, this could lead
to an incoherent state between topology and measurements and to a problem in state
estimation.
To minimize the probability of occurrence of this problem, we apply a very important and
classical rule to generate a snapshot
We wait 20s to generate a snapshot after the reception of the last switching device
status.
A snapshot is generated after 1mn even if the condition isnt fulfilled
Presentation of SE in RTE
t t+10
Measurements (t)
Measurements (t+10)
switching
Inconsistent
Snapshot
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Observability :
A numerical observability is used, with a decoupled Jacobian matrix.
better numerical robustness in SE
Critical pseudo-measurements are added in unobservable areas to restore
observability.
no effect on estimated states
The EHV network is more observable than HV network.
pair measurement s ( P,Q) in EHV sometimes not in HV
The percentage of observable nodes varies from 80% to 92%.
Presentation of SE in RTE
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Presentation of SE in RTE
Computing algorithms :
For real time : A classical L2 cost function is minimized using Gauss-Newton
algorithm
For off line data validation : A M-estimation function is minimized using a trust
region method based on Luvember-Marquardt algorithm.
Estimation of OLTC taps, there are two steps :
First step : ratios of transformers are considered as continuous variables
Second step : ratios are fixed to the nearest discrete value
For each node, the estimated nodal injection is dispatched among loads and
generators
Maximum values are taken into account
If the estimated nodal injection is greater than the total of maximum values, a fictitious
load is created to balance the s stem.
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Presentation of SE in RTE
Bad data detection :
Detection of bad data is based on a 2 test.
If2 test fails, we use normalized residuals to detect bad data
an iterative process deletes one by one bad data and reruns a SE (maximum 10 iterations)
This approach suppose that only measurement may be contaminated by bad
data. This hypothesis is not always satisfied, in this case robust state estimation
helps to find the problem.
We define two kind of robustness:Numerical robustness, it deals with the reduction of divergence
Trust region method
Bad data robustness, which reduce the bad data effect.
M-estimator rather L2 estimator
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Presentation of SE in RTE
Visualization
The same tool in :
Real time
Study mode.
we can load a snapshot (green :
observable, red : unobservable)
For each substation, a comparison is
possible between :
Estimated state
Measured state
Figure : The EHV network of RTE (study mode)
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Presentation of SE in RTE
Visualization :
Figure 2 : 400kV substation , measured state Figure 3 : 400kV substation , estimated state
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Use of SE in RTE
a. Real time operations :
State estimation builds a coherent state before any contingency analysis.
b. Building of reference base cases :
From 2 to 4 reference cases per day are built, which are used to build forecast casesfor operational planning , for ATC computation, .
We developed a collaborative process between our 7 regional control centers and
our national control center
Building of reference base cases : principles
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2008 IEEE PES General Meeting: Panel on Best Practices in State Estimation, 11
Initialization by National Control Center
Import snapshot of Region 1
EHV-HV
Import snapshot of Region 7 EHV-
HV
Merging of 7 regional snapshots (EHV-
HV)
Export state of Region 1 EHV(National)-
HV(regional)
Export state of Region 7 EHV(National)-
HV(regional)
manual validation
(Region 1)
manual validation
(Region 7)
Merging of 7 regional corrected states
(EHV-HV)
Final manual validation by NCC (EHV-HV)
Export final corrected state of Region 1
EHV(National)-HV(regional)
Export final corrected state of Region 7
EHV(National)-HV(regional)
.
.
Building of reference base cases : principles
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Manual Validation based on quality criteria
SE quality criteria :
Number of iterations or divergenceNumber of unobservable nodesRate of redundancyNumber of fictitious loadsPossible inconsistencies between topology and measurementsNumber of critical measurementsNumber of bad data
A change of one these criteria requires an analysis
A global quality index based on these criteria is given to each
reference base case.
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Building of reference base cases : Work Flow monitoring
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Most important challenges
We need to have more coordination between European TSOs, an
European network model is mandatory Hierarchical SE.
The robustness of state estimation :
Still a challenging subject No substation internal measurements transmitted => difficult to detect an erroron topology
A state estimation running at the substation level could improve the situation. Ensuring the consistency between topology and measurements, full coherent
state transmitted (status of switching devices and measurements for example
each 1 sec.).
To improve the measurement system, the worst stage must be
improved first.In our case the first limiting factor is the LAN at substation level ( old protocol
using 8 bits for measurements).