Resource Adequacy and Transmission Security of the Bulk Power System

How Hurricane Sandy may have impacted New York Independent System Operator's "2012 Reliability Needs Assessment Report" and broadened the range of technical solutions considered for improved grid reliability.


How Hurricane Sandy may have impacted New York Independent System Operator's "2012 Reliability Needs Assessment Report" and broadened the range of technical solutions considered for improved grid reliability.

By Dave Bryant

On Sept. 18, 2012, just 42 days before Hurricane Sandy hit New York City, the New York Independent System Operator (NYISO) published its "2012 Reliability Needs Assessment Report." The report provided a 10 year forward assessment of resource adequacy and transmission security of the New York bulk power system, based on assumptions, scenarios, reliability criteria and historical base-case data that included the planned retirement of several facilities and the addition of others—generation and transmission assets—currently under construction.

The report described a reliability need as the potential inability of the electric system to supply the aggregate electrical demand and energy requirements at all times, taking into account scheduled and unscheduled outages of system elements. The report went on to assess resource adequacy and transmission security. Transmission security was defined as "the ability of the power system to withstand disturbances such as electric short circuits or unanticipated loss of system elements."

At the time the report was written, it is doubtful the impact of the largest Atlantic hurricane on record, Hurricane Sandy, was considered. Nevertheless, given a wide range of scenarios during the 10-year study period, many potential transmission security violations were identified on the bulk power transmission system. Various solutions can then be considered, which ultimately allow market-based and regulated solutions to be requested and tied into the development of a comprehensive reliability plan with stakeholder involvement. In the wake of Hurricane Sandy, however, it is likely these requests will be greatly expanded and enhanced, and new, innovative solutions will be sought and implemented as market forces dictate.

While assessing scenarios, the NYISO's transmission analysis identified many "thermal violations." Thermal violations refer to a situation where existing transmission lines are forced to carry additional current, which, if not quickly resolved, cause conventional overhead conductors to overheat and sag. As experienced during the 2003 Northeast blackout, excessive conductor sag can cause short circuits and cascading outages. It is likely, therefore, that in many cases, high-capacity, low-sag conductors such as aluminum conductor composite core (ACCC) will be deployed to mitigate this fundamental problem.

While effort is being directed towards building a smart grid using meters, electronic sensors and telemetry devices, telemetry devices have limitations. It is important to use robust structures and conductors that can withstand high stress levels encountered during storm conditions. While flying debris and short circuits cannot be completely avoided, a robust grid can minimize downtime and enable crews to re-energize lines more quickly and efficiently.

Though new, the ACCC conductor is some 40 percent stronger than other high-capacity, low-sag conductors such as aluminum conductor steel supported (ACSS). ACCC conductors have been deployed to more than 225 project sites, the first in 2004 in Niagara Falls, N.Y., by Niagara Mohawk, a subsidiary of National Grid. The line reportedly survived several substantial ice storms without incident.

On the opposite side of the spectrum, a severe January 2012 fire near Reno, Nev. burned down wood H-frame structures, causing the ACCC conductor and metal cross-arms to drop to the ground. The metal cross-arms and the ACCC conductor were undamaged. The wood poles were replaced and the cross arms and conductor lifted back into position and re-energized within hours.

While much of NYISO's analysis considered early retirement, interruption or addition of generation resources and transmission assets, consideration also was given to the continuation of energy efficiency programs, demand response programs, and the impact of new and proposed environmental regulations on the existing generation fleet.

Another attribute new conductor technology offers—besides high strength, increased capacity and low thermal sag—is improved efficiency. As transmission lines carry higher levels of current, some 4 to 5 percent of the generated electricity is lost to heat because of the wire's electrical resistance. The ACCC conductor exhibits reduced electrical resistance, which translates into a reduction of line losses by some 30 percent or more. Reduced line losses can reduce generation capacity requirements, reduce fuel consumption and reduce associated emissions. When considering a fossil fuel fired plant, these emission reductions can be substantial.

Another objective of NYISO's "2012 Reliability Needs Assessment Report"—and subsequent action plans—is to consider congested transmission lines. Congested transmission lines—meaning the lines are no longer capable of handling as much current as demand requires—are significant as it relates to grid reliability (especially during an N-1 event), and congested transmission lines can drive up the cost of electricity to the consumer, especially when less expensive electricity sources can no longer be delivered to load centers during high demand periods.

Using high-capacity, low-sag conductors can mitigate congestion costs and improve grid reliability. Hopefully, the lessons of the past will help us build a more robust, reliable and efficient grid. Some might call that "a very smart grid."

About the author: Dave Bryant, director of technology, CTC Global Corp. of Irvine, Calif., was a co-inventor of the patented ACCC conductor and ancillary hardware components. Bryant is an active member of many industry associations and was the primary editor of "Engineering Transmission Lines with High Capacity Low Sag ACCC Conductors."

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