State Estimator Tuning and External Network Model Development

The state estimator and associated data modeling are key to the success of EMS advanced applications and modern market operations. Nexant has more than 100 man-years of experience in state estimation and external modeling.

State Estimator Tuning. For a given state estimator installation, whether at the time of commissioning or after the system is in place, Nexant can assist by improving both the frequency and quality of the estimator's convergence. We have at our disposal very powerful analytical and diagnostic tools in the form of study-mode versions of our industry-leading GEN-SE® state estimator and TOPAZ® topology estimator. These facilitate the following contributions to improved state estimator performance:

• Achieve significant reductions in convergence mismatches (residuals)
• Identify and eliminate analog telemetry errors
• Identify and correct status and topology errors
• Identify and correct parameter errors
• Improve solution veracity by modeling power-flow-type local controls
• Perform plausibility analysis
• Identify the numbers and locations of critical measurements
• Adjust measurement weights
• Identify locations where more measurements are needed for reliable estimation
• Analyze phasor measurement (PMU) reinforcement

External Network Model Development. For dispatcher power flow, contingency analysis, and all forms of network-constrained dispatch (optimal power flow) the EMS network model must include all power system elements that can have significant effect on the flows and voltages in the "internal" network (i.e. the network under the direct supervision of the EMS). Often such elements are in the "external" network. For faithful modeling of the internal system flows and voltages under all foreseeable conditions, the questions then are (a) which elements of the external network must be explicitly retained, (b) which external elements can be discarded and which need to be lumped into equivalent impedances, and (c) which external measurements, associated with the retained external elements, are needed.

Nexant's MODELEX® package explicitly addresses these complex, specialized and important issues, and is the only analytical software of its kind. It represents the state-of-the-art in automated network sensitivity analysis, equivalencing and reduction. MODELEX enables its users to determine quickly and easily how much of the external system has to be modeled and what external data is essential. In a large interconnected network MODELEX typically produces remarkably small external models that adequately preserve the accurate representation of internal network power flow and voltage conditions. MODELEX also allows unnecessary parts of the internal system (e.g., those at low voltages) to be identified and eliminated.

Nexant offers consulting services using MODELEX to create and maintain reliable external network models for EMSs.