1. Enhanced State Estimation by Advanced Substation Monitoring PSerc Project Review MeetingTexas A&M University November 7, 2001 College Station, TX PIs: Ali Abur, Mladen Kezunovic Research Assistants: Shan Zhong, Sasa Jakovljevic

2. Outline n Objectives n Technical Approach n Implementation n Results n Conclusions

3. Objectives n Utilization of CPU and Data Acquisition Capabilities at the Substations n Application: Topology Error Detection and Identification n Integration of Substation Processor and the EMS State Estimator n Effects of Unbalanced Operation on Estimated State

4. Technical Approach n Pre-process substation measurements n Develop a two-stage state estimator u Conventional model: first stage u Expanded model: second stage n Validate performance for topology errors n Investigation of other error sources: unbalanced operation n GUI Development and testing

5. Implementation: Substation Monitoring/ Measurement Processing F Processing & consistency check algorithms F Substation measurement simulation software

6. Substation Model n SIMULINK part of the model Simulation of substation measurements F Voltage measurements F Current measurements F Contact status measurements Exporting simulation data into file n MATLAB part of the model F Data preparation F Description of the measurement placement & topology F Consistency check using developed algorithms F Exporting substation State Estimation results to tables

7. State Estimator n First Stage F Uses LAV method to estimate the state of the system F Normalized residuals are used to decide on the suspect substation(s) if there exist any. n Second Stage F Uses detailed models for the suspect substations F Advanced substation state estimation of suspected substation represented in detail F Enhancing the state estimation of overall power network by including substation data

8. Interaction between System SE and Substation SE Exchanging data F Conventional residual calculation and determination of suspected substation F Advanced substation state estimation of suspected substation represented in detail F Enhancing the state estimation of overall power network by including substation data n Program for data conversion (interfacing) F Converts data in real time after each data snapshot F Utilizes the established format for data exchange

9. Testing: Types of Topology Errors n Type1: Merged Bus The correct status of the CB is closed, but it is assumed to be open. n Type2: Split Bus Opposite case of type 1 error. n Type3: Line Outage The correct status of line end CB is closed, but assumed to be open. n Type4: Line in Service Opposite case of type 2 error.

10. Library of Topology Errors n Based on IEEE 30 bus system n 50 Cases of different kinds of scenarios

11. Performance Evaluation n Type 2 and type 3 errors are easily identified n Methods that utilize the normalized suspect measurement incidence index perform better n Limiting the number of suspect measurements also improves the performance n All the cases can be identified by slightly increasing the maximum suspect substation number

12. Graphical User Interface for the Two-Stage State Estimator

13. GUI Features: n Creation of substation model from scratch n Creation of a substation model using the template n Automatic Generation of Substation Measurements

14. Three Phase State Estimator Features: F Three phase measurements F Structural unbalances (tower geometry) are modeled F Unbalanced loads/generation are modeled Utilization: F Study the effects of neglecting unbalances in SPSE F Study the feasibility (practicality) of its utilization from the view point of network data and measurement requirements

15. Observations: n Under certain cases, the use of single- phase state estimator may lead to significant biases in the solution due to existing asymmetries or load unbalances. n A higher sensitivity is observed of the system state to loading unbalances than to asymmetries in the transmission line conductor configurations

16. Conclusions n Substation measurement pre-processor improves the central State Estimator performance n Three phase unbalances are potential sources of error and should be considered n Synchronized measurements between substations can improve the benefits of the pre-processing function