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OPERATIONAL EXPERIENCE WITH STATE ESTIMATION AT HYDRO-QUÉBEC

OPERATIONAL EXPERIENCE WITH STATE ESTIMATION AT HYDRO-QUÉBEC. S. Lefebvre, J. Prévost , J.C. Rizzi, P. Ye (IREQ) B. Lambert, H. Horisberger (TransÉnergie). Network description. Main network Generation Installed capacity of around 38 000 MW

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OPERATIONAL EXPERIENCE WITH STATE ESTIMATION AT HYDRO-QUÉBEC

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  1. OPERATIONAL EXPERIENCE WITH STATE ESTIMATION AT HYDRO-QUÉBEC S. Lefebvre, J. Prévost, J.C. Rizzi, P. Ye(IREQ) B. Lambert, H. Horisberger (TransÉnergie)

  2. Network description • Main network • Generation Installed capacity of around 38 000 MW Over 95% of the generation is hydro (soon 4000 MW of wind!) Asynchronous with the rest of North America • Transmission 735 & 315 kV AC systems Multi Terminal DC line 450 kV (over 1000 km) 4 back to back DC Terminals (soon 5!) • Sub transmission 230, 161, 120 & 69 kV AC systems

  3. Network Description (next …) • 735 kV Grid • Components • 11000 km of lines (charging around 33 000 MVAR) • Series capacitors: 12 000 MVAR • Switched inductors: 25 000 MVAR • Switched capacitors: 13 000 MVAR • SVC & SC: -3800 – 5800 MVAR • Characteristics • Operation constrained by stability and voltage limits(almost no thermal limit) • Generally operated well under the SIL (lines switching can even be used for voltage control) • Ramping rate becoming more and more important ( 200 MW/Min.)(may even cause voltage control difficulties) • Corona effect may suddenly become important(may reach over 2 times the thermal losses: e.g. 1000 MW)

  4. Current status of system control • Hydro Quebec EMS/SCADA control centers • One Provincial control center (EMS) and one back up center • Responsible of the bulk transmission grid (735 to 315 kV) • Main Functions: - Data acquisition - Automatic Generation Control - Economic Dispatch - Security Analysis - Exchange management - Outage Management - Voltage control • Seven regional control centers (SCADA) • Responsible of the sub transmission grid (230 kV to 69 kV) • Main Functions: - SCADA (for the full HQ’s network) - Outage Management • Operations are usually triggered by operators from the provincial center and then are executed by operators at the regional centers

  5. State estimation experience • LASER0 • In-house product • Pd and QV decoupled algorithm • Model: 735 kV network • LASER1 • Commercial product: ABB • In house simple pre-processing topology error function • LASER2 • Commercial product: SNC (formerly CAE) In house elaborate pre-processing topology error function

  6. State estimation latest development at HQ’s • Archiving system • In-house product • Main functions:- Static network model (CIM/XML) saved after each DB update - Dynamic raw input/output of SE function saved at each RTS run - Power flow case (IEEE) saved after each RTS run • Matlab SE toolbox • In-house product • Main functions:- Real time snapshot handling - Sub network extraction (by substation or voltage level) - Measurement system analysis (redundancy, identification of critical meas.) - SE algorithms (WLS, Huber, DWLS) - Cases modification & comparison - Parameter estimation - Monte Carlo simulations (evaluation of the solution sensitivity & precision)

  7. State estimation latest development at HQ’s (next …) • Reporter • In-house product • Main goal: Identification of topology and measurement errors Robust approach (no false alarm) • Operate on a continuous base (24/7) • Independent of SE solution (convergence, false rejected meas., …) • Based on a heuristic approach: a set of rules, combinatorialanalysis and iterative processing • Takes advantage of previous network & telemetry data (Hn-1, Zn-1) • Filtering reporting capability (already know bad modeling, …) • Historical reporting capability (error, start & end time, frequency, …) • Others reporting possibility (performance index degradation, …) • Web & email reporting (used by the support engineer team)

  8. SE model Near half of switches are breakers that are 100% telemetered The other half is reconfigu- ring switches and only 70% are telemetered. Thus over 750 switches are based on a manual entry Moreover not all switch are modeled. By example maintenance switches are rarely modeled

  9. SE measurements and their redundancy The 735 transmission grid model has a very good redundancy (4.1). The sub-transmission grid model has a lower redundancy (2.6) QV redundancy (3.5) is much higher than its Pd counterpart (2.0)

  10. SE problems • Topology error • Originate mainly from maintenance work • Bad series switch status (bus split/merge more diffcult to identify) • Bad shunt switch status (more diffcult to identify) • Q-V model more complex, more sensitive and less accurate than P-d model • A important quantity of reactive (accuracy can become a problem) • A lot of elements (Serie cap, reactors, SVC, …) • Weather dependant parameters • Corrona effect (from almost 0 to 2 times thermal losses) • Temperature (from -40 celcius to +40 celcius -> 30% of errror)

  11. SE model is never exact • Inequality constraint cannot be model (ex: power limit, …) • Mutual effect cannot modeled (ex: on double circuit Z11~ 5%*Z1) • Complex equipments (DC, SVC, …) generally can only be modeled as simple injection • Variable system parameters as affected by temperature and humidity are generally not considered (ex: corona loss , …) • Three-windings transformer generally modeled as two-windings • Constant LTC Transformer impedance often used • Isolation switches and/or breaker not always modeled(represented only in their normal position) • Small load not always modeled (auxiliary service) • Network modification (ex: new line) not always in sync with the model • Transmission line parameters calculation often based on typical values (height, span, sag)

  12. SE measurements is never exact • Manual entry inaccuracy (switch status, …) • Presence of time skew (ex: 25s. between provincial and the regional centers)(ex: manual entry can be delay by several minutes) • Measurement dependency (V, I, P, Q) • Presence of dead bands in the acquisition chain • Measurement bias (e.g. in CCVT) • Presence of unbalance (zero and negative sequence) • Use of phase measurements vs sequence (direct) measurements • Variable standard deviation (s = f(burden))

  13. SE solution quality Relative Performance index (%)

  14. SE usage (example 1) Topology error detection: Side effect 905 -1 VOLT 735 744.2 749.3 14.2 -0.7 0-J 735 0.0 0.0 0.0 0.0 JAC CAR LINE L7018 CP 1023.0 -189.0 40.1 -118.3 EW XFR2 T1 735 -40.1 118.3 906 -1 VOLT 735 743.6 740.9 25.0 0.4 0-J 735 0.0 0.0 0.0 0.0 CHAMO LINE L7026 CP -864.0 -24.0 -243.9 -82.0 EW MICOUA LNSX L7019 CP -822.0 -111.0 -478.4 -143.9 EW XFR2 T2 735 722.3 226.0 907 -1 VOLT 735 731.7 23.9 0-J 735 0.0 0.0 0.0 0.0 MICOUA LINE L7019 -478.5 -298.4 S-D CXC15010 478.4 298.4 Topology error Wrong manual entry

  15. SE usage (example 2) Parameter validation: Double circuit of short length, modeled as equal lengthbut in reality not exactly the same length

  16. SE usage (example 3) Accurary improvement: Flow735: smeas/ sest> 3 « Limite sud » flow evaluation: Measurements accuracy: 3s =360 MW Estimates accuracy: 3s = 120 MWCan increase the margin by 240 MW!!!

  17. Corona evaluation & minimization: SE usage (example 4) Average: 8 MW loss reduction (1%) Improved by voltage control (low & flat)

  18. SE usage (example 5) Loss evaluation & minimization: Average: 33 MW loss reduction (4%) Improved by voltage control (high & flat)

  19. Conclusion • Need for SE Technology that can handle more appropriately practical issues • Adding more measurements is not always the solution(although useful) • SE does not only provide states (X) but also a model (H)So, even if PMU may help, it will not solve all problems • Model & errors/inaccuracies cannot be avoidedSo, model should not be considered as “hard constraint” (at least for parameters like R & G, and may be even X for LTC!) • All information available should be used (inequality constraint, setpoint, previous data (Zn-1, Hn-1), quality (manual, telem., …),tag • Electrical topology (not necessary physical) error detection, identification and correction function should be de facto available • Sudden quality change (residues, rejected meas., …) should trigger a validation mechanism

  20. Conclusion • Need for SE support tools • Quality indexes evaluation (standard indexes will also be nice!) • Measurements analysis (critical meas., local redundancy, …) • Model analysis (parameter estimation, sensitivity, …) • Solution analysis (estimate accuracy, robustness in regard of meas. loss, …) • Visualization tools for analysis and debugging (ex:3D diagram showing residues, biases, rejected meas.) • Model validation tools (modification, solutions comparator, …) • Improved SE solution quality will increase its role • Transmission optimization (LM, DSA, …) • Market operation (ED, …)

  21. Questions ?

  22. Provincial / area Control Center Power plant / Transmission substation Sub transmission substation Distribution control center Distribution feeder Hydro-Québec TransÉnergieControl centers architecture Phone IEC 60870-5 ICCP Regional Control Center DNP3 7 DNP3 Proprietary MODBUS .. Phone

  23. Power flow optimization State estimation Limit service frequency control Contingency analysis Regional control centers Remote terminal units Hydro-Québec TransÉnergieProvincial control center (main information functions & information flows) Limit violations Switching advices Flow limits ATCs Controlorder Network solution Snapshot SCADA Setpoints The real-time sequence (RTS) of the network analysis tools runs every minute (500 full AC contingencies, 5 min) Telemetry

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