Examining reliability impact of renewables

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As directed by the Energy Policy Act of 2005, the North American Electric Reliability Corporation (NERC) must conduct periodic assessments of the reliability and adequacy of the bulk power system (BPS). To that end, NERC has released an independent review of bulk power system trends to analyze the state of reliability and provide an integrated view of reliability performance.

Key findings, among others, will serve as input to NERC’s risk assessment and Reliability Standards project prioritization, compliance, process improvement, event analysis, reliability assessment, and critical infrastructure protection.

NERC found that the daily severity risk index (SRIbps) value, which measures risk impact or “stress” from events resulting in the loss of transmission, generation, and load, has been stable to improving from 2008 to 2013, NERC found. In 2013, there were no high-stress days, including weather events. During 2008-2013, the majority of high-stress days were weather-initiated or exacerbated. AC transmission circuit availability remained above 97 percent, and transmission transformer availability was above 98 percent from 2010 to 2013, including both forced and planned outages — demonstrating that the BPS is able to perform reliably over a variety of operating conditions.

Frequency response remains stable, according to the report. All interconnections have shown steady frequency response performance, trending above the recommended obligation at all times during the study period. NERC will examine incidents in 2013 where frequency response was less than interconnection frequency response obligation, and determine how to maintain and improve frequency response performance.

Protection system misoperations continue to be a significant contributor to automatic transmission outage severity. NERC has identified system protection reliability, uncoordinated protection systems, and protection system misoperations as top-priority risks to reliability and is focusing its Reliability Standards efforts in these areas, with the completion of the relay loadability standards and continued work on relay misoperations and coordination.

NERC continues to examine impacts related to the changing levels of variable resources such as wind, solar, and hydro, noting that the BPS will require significant changes to traditional methods used for system planning and operation. The amount of variable generation is expected to grow considerably as policy and regulations on greenhouse gas emissions are being developed and implemented, making it crucial to consider the impacts of variable generation in power system planning and design and develop the necessary practices and methods to maintain long-term BPS reliability.

NERC is defining essential reliability services and possible sources for those services and expects to form a task force to continue this work.

For more:
– see the report