1 Abstract— In this paper, the relevance of the State Estimator (SE) solution used in real time operations and the availability and performance criteria used to determine SE’s readiness for these applications for grid security and market operations at California ISO (CAISO) are discussed. In order to enhance the performance of the SE, CAISO updated the SE algorithm from the Fast Decoupled (FD) method to the Orthogonal method. The detailed comparisons of the SE performance based on the two methods are presented in this paper. While the SE solutions continue to be used by traditional EMS applications at CAISO, this paper focuses on SE solutions used by two new applications in real time. These are (1) CAISO Nodal LMP Real Time Market and (2) Security Applications such as Voltage Stability Analysis (VSA). The approach used to transfer the Real Time SE solution to these new applications, using the XML data format, is also discussed. NOMENCLATURE— Automatic Load Forecasting System (ALFS), California Independent System Operator (CAISO), California Mexico Reliability Coordinator (CMRC), CAISO Outage Modeling Tool (COMT), Common Information Model (CIM), Contingency Analysis (CA), Dispatcher’s Load Flow (DLF), Energy Management System (EMS), Extensible Markup Language (XML), Fast Decoupled (FD), Full Network Model (FNM), Inter-Control Center Communications Protocol (ICCP), Load Flow (LF), Locational Marginal Price (LMP), Look Ahead (LA), Market Redesign and Technology Upgrade (MRTU), Midwest Independent System Operator (MISO), Online Study (OS), Outage Scheduler (OUS), Participating Transmission Owner (PTO), Positive Sequence Load Flow (PSLF), Real Time (RT), Real Time Market (RTM), Real Time Pre Dispatch (RTPD), Real Time Interval Dispatch (RTID), Dinesh Salem-Natarajan, Liang Zhao, Wei Shao, Matthew Varghese and Soumen Ghosh are with California ISO, Folsom, CA. Mani Subramanian and Gordon Lin are with ABB Network Management, Sugar Land, TX. Hsiao-Dong Chiang is with Cornell University Ithaca, NY and Hua-Li is with Bigwood- Systems, Ithaca, NY. Invited Panel: Best Practices in State Estimation- Paper 08GM0265 Real Time Data Base (RTDB), Service Oriented Architecture (SOA), Southwest Power Pool (SPP), State Estimator (SE), Supervisory Control And Data Acquisition (SCADA), Supplemental Market Data Management (SMDM), Voltage Stability Analysis (VSA), Western Electricity Coordinating Council (WECC). I. INTRODUCTION A more and more reliability tools and market systems depend on the results produced by the SE, it is natural that there is an ever increasing interest in analyzing the quality of every SE solution and monitoring the availability and the quality of the solution over a period of time. At CAISO, the SE solution is planned to be used in the Real Time Nodal Market and the Voltage Stability Analysis applications. These two applications are scheduled to go online in the 2 nd quarter of 2008. In late 2006, the SE readiness evaluation committee was formed at CAISO to evaluate the readiness of SE for the applications mentioned above. In the evaluation of SE readiness, several guidelines for SE availability and performance metrics used by the Midwest ISO (MISO) and Southwest Power Pool (SPP) were reviewed [1, 2], and a set of guideline metrics were established. Also, several new SE performance metrics of the SE solution at the CAISO have been identified and are being monitored since the beginning of 2007 by the SE Readiness Team. The new SE performance metrics were selected based on their ability to identify an unreasonable SE solution that would have otherwise been declared to be valid in the traditional method. This paper discusses the extent of CAISO Network Model (EMS Model) footprint; the Market Model footprint; the representation and maintenance of these models in CIM/XML format; the relevant EMS applications currently online; the implementation of VSA; Orthogonal SE and its comparison with FD SE; the relevance of SE solution in Real Time Nodal Market and VSA; the SE Readiness Metrics adopted at CAISO and the proposed acceptable range of the metrics. Additionally, as more and more entities become interested in the subject, it is the authors’ hope that this paper would set up a framework for the industry to work collectively in identifying a standard set of SE availability and performance metrics that can be used to determine the quality of the SE State Estimator for CA ISO Market and Security Applications – Relevance and Readiness Dinesh Salem-Natarajan, Liang Zhao, Wei Shao, Matthew Varghese, Soumen Ghosh, Mani Subramanian, Gordon Lin, Hsiao-Dong Chiang, Hua Li ©2008 IEEE.