gestionnaire du réseau de transport d 'electricité 2008 ieee pes general meeting: panel on...

2008 IEEE PES General Meeting: Panel on Best Practices in State Estimation

Gestionnairedu Réseau de Transport d 'Electricité

Experiences and practices on State Estimation in

RTE (French Transmission System Operator)

Patrick Panciatici (RTE), Yacine Hassaine (RTE)

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 network’s 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 state Measurements, Topology Electrical characteristics

StateEstimation


Equivalent networks


National level : SE runs every 5mn400 kV and 225 kVA part of external surrounding networks is represented in details( size around 1200 nodes)

Regional level (7):SE runs every 10mnFrom 63 kV to 400 kVA part of external surrounding networks is represented in details.(average size around 1000 nodes)

National or Regional network

Surrounding networks

Network modeling :


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 isn’t fulfilled


t t+10

Measurements (t) Measurements (t+10)

switching

Inconsistent Snapshot


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%.




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 variablesSecond step : ratios are fixed to the nearest discrete value

For each node, the estimated nodal injection is dispatched among loads and

generatorsMaximum values are taken into accountIf the estimated nodal injection is greater than the total of maximum values, a fictitious load is created to balance the system.



Bad data detection : Detection of bad data is based on a 2 test.

If 2 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



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)



Visualization :

Figure 2 : 400kV substation , measured state Figure 3 : 400kV substation , estimated state


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 cases for operational planning , for ATC computation, … .

We developed a collaborative process between our 7 regional control centers and our national control center


• 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


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 measurements Number 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.


Building of reference base cases : Work Flow monitoring


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 error on 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).• Calibration of CVT, …

gestionnaire du réseau de transport d 'electricité 2008 ieee pes general meeting: panel on...

Documents

se maximum

kind of measurements

coherent state measurements

detection of bad data

measurements tmeasurements

secritical pseudomeasurements

rtebad data detection

estimation function