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Reliability Monitoring: The High-Tech Eye In the Sky

How reliability performance monitoring and standards compliance will be achieved in real time.

Fortnightly Magazine - January 2007

utilizes real-time data from all NERC North America control areas. As shown in Figure 1, data are updated by the control areas every four to six seconds and sent automatically via the NERC Wide-Area Network to a central server at NERC’s headquarters in Princeton, N.J. The ACE-Frequency system reads and processes these data and converts them into meaningful monitoring metrics and wide-area, geographic visual displays that can be accessed, via a secure Internet connection, by NERC reliability coordinators, control area operators, and members of the NERC Resources Subcommittee.

The system automatically sends alarms in real time (in the form of electronic e-mails and pages) when interconnection frequency strays outside of normal limits, and when specific NERC-reliability performance metrics are violated. The alarms inform the reliability coordinators of load-generation resource inadequacies (ACE-Frequency imbalance) and provide summary information, which enables them to search systematically for root causes and to identify remedial actions. Figure 2 provides a step-by-step illustration of how the ACE-Frequency system currently is used.

Challenges in Reliability Compliance Monitoring

The early success of the ACE-Frequency collaboration suggests that there are both great potential and great challenges for further research on new technologies to improve grid reliability management and oversight. DOE’s collaboration with NERC continues to evolve to meet these challenges.

The initial goal of the DOE-NERC collaboration was to prevent a recurrence of the summer 1999 low-frequency events described above. However, addressing that series of events led to identification of far more pervasive and widespread frequency issues in the Eastern Interconnection.

In Figure 3, a box plot of daily epsilon, which is a measure of performance, shows that reliability control is deteriorating in the Eastern Interconnection. Underlying this problem is declining generator performance, specifically in response to frequency excursions (see Figsures 4 and 5) . Left unchecked, this decline will pose a direct threat to the interconnection’s future reliability.

To address this concern, CERTS supported the NERC Resources Subcommittee in research and development of new reliability metrics. CERTS continues to support NERC Standard Drafting Teams, including the Balance Resources and Demand Standard drafting team, in validating and field-testing the new reliability metric, called the Balancing Resources and Demand (BRD) performance metric with a threshold for each balancing authority called the Balancing Authority ACE Limit, or BAAL. The shortcomings of the old, long-standing Control Performance Standard 2 (CPS2) metric, are addressed by the BRD metric. In the past, the CPS2 often led to unneeded and sometimes uneconomic control actions, which under some conditions could further degrade interconnection frequency.

The new BRD metric addresses these shortcomings by linking a control area’s ACE compliance with the impact of this compliance on interconnection frequency, including explicit consideration of risk, in establishing acceptable frequency limits. The drafting team will complete a field test of the new metric with selected utilities serving almost half of the Eastern Interconnection in the fall of 2006. A recommendation to adopt a revised standard is expected to follow.

Implementing Recommendations From the 2003 Blackout Investigation

The U.S.-Canada final report on the Aug. 14, 2003, Eastern Interconnection blackout contains 46 recommendations. The following