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State Estimator Telemetry

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State Estimator Telemetry

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    1. State Estimator & Telemetry

    2. Imagine a student measuring current on an electrical circuit

    3. Imagine a student measuring current on an electrical circuit

    5. But what if you do not know the accuracy of the instruments A state estimator is a minimization program, which minimizes the sum of weighted residuals. In this example, we assumed meter 1 had a measurement accuracy of +/- 1.666% standard deviation. (i.e. 99.9% of measurements would be within 5%), and meter 2 had a measurement accuracy of +/- 2 standard deviations.

    6. But what if you do not know the accuracy of the instruments If you have no idea of the expected accuracy of the instruments, then a reasonable approach is to average the two measurements. (.56 + 1)/2 = 0.78 A This is obviously not correct from our previous analysis: so a basic requirement is to know the expected accuracy of your measurements.

    7. Proposed Telemetry Requirement 1: TSPs and QSEs shall notify ERCOT of the expected accuracy of their analog measurements. Preferred format is expected accuracy of PT, CT, A/D converter and transducer in percentage. TSPs & QSEs will identify how the accuracy was calculated: i.e. Calculated from manufacturer specifications these devices (high confidence) MFG specs unavailable: estimated from typical specifications historically installed by our company A guess from our experience.

    9. Proposed Telemetry Requirement 2 When ERCOT identifies a measurement which is probably in Error, Participants shall recalibrate the device within 2 working days or provide ERCOT with data documenting reasons that the measurement is known to be correct. Each TSP and QSE shall have a telemetry calibration program which can be shown to maintain the probable number of devices outside of their specified accuracy range to < 1% OR alternatively shall be re-calibrated once every 2 years.

    10. Imagine our student takes both meters to his Teaching Assistant, and asks him to check them. To his surprise, the instructor returns them 15 minutes later, telling him they both check out. What should he do? Logically he should ask how the meters were calibrated.

    11. Proposed Telemetry Requirement 3 If a TSP or QSE examines a measurement at the request of ERCOT, and no error is detected, the TSP or QSE shall provide ERCOT with details of how the calibration took place.

    12. State Estimator

    13. State Estimator

    14. State Estimator

    15. State Estimator

    16. State Estimator Weighting Calculation Stdv =(PTE+CTE+ADCE+TRE)*Base/(Probable Max stdv based on gaussian distribution=5) Example: If PT error = 1% (.01); CT error = 1% (.01); transducer = 1% (.01) and AD converter accuracy = 1% (.01) on a 271 MVA line than the expected standard deviation of the measurement mapped to that line is: (.01+.01+.01+.01)*271/5 = 2.61 and the weighting is 1/SD2 = 0.14679 Now the Performance index = the sum of these weighting factors * residual or: PI = S Weight Factor(i) * Residual(i)2 So what information do we need for each measurement? Accuracy of PT (maximum error) Accuracy of CT Accuracy of A/D converter Accuracy of transducer

    17. State Estimator

    18. State Estimator Default Weight Calculation For a 1000Mva line belonging to MEAS class has Stdv = (.01+.01+.01+.01)*1000/5=8, w=1/64 For a load with parent fraction 10 has Stdv = (.01+.01+.01+.01)*10/5= .08, w=1/.0064

    19. BREAK

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