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POWER ENGINEERS SUPPORTING TRUTH
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The Need For Strong Planning and Operating Criteria To Assure A Reliable Bulk Power Supply System
Prepared by F.J. Delea, J.A. Casazza, G.C. Loehr and R.M. Maliszewski Power Engineers Supporting Truth
Following the 1965 Blackout more than 35 years ago, most of the power systems in North America formed associations called Regional Reliability Councils to promote the reliability of bulk power supply. These councils developed and adopted a series of planning and operating standards or “criteria” for the design and operation of a reliable electric power supply system. Each Regional Council established criteria consistent with the nature of its member power systems and the characteristics of the areas they served. All members were obligated to plan and operate their systems in accordance with these regional standards.
Even though each region developed its own criteria, there was a high degree of consistency among all of the regional criteria. Differences were recognized as necessary to reflect the characteristics of each region, and the criticality of the areas served. For example, the systems in the Northeast, particularly in New York, developed more stringent standards than those in some other areas of the country because of the importance to the nation of a reliable power supply to the New York City load area. Each Region’s criteria also recognized the unique characteristics of its geographical area and its electric system. For example, the New York City area has a very high load density, limited transmission supply options, and a vast underground cable system.
In 1969, the Regional Reliability Councils established the National Electric Reliability Council – subsequently renamed the North American Electric Reliability Council (NERC). Through NERC, overall reliability standards were developed. These have always been considered minimum standards. All of the regional criteria are in conformance with the NERC standards as a minimum; but some regions, such as the Northeast Power Coordinating Council (NPCC), maintain more stringent standards for the reasons cited above. NERC standards are the minimum – national standards should always be minimum rather than absolute or “one size fits all” criteria. Densely populated areas, like the metropolitan areas of New York, Chicago or Washington, must be designed and operated in accordance with a higher level of reliability than would be appropriate for sparsely populated parts of the country. It is essential that regional differences in terms load and population density be recognized in the application of planning and operating criteria. Any move to adopt a national, “one size fits all” formula for all parts of the United States would be disastrous to reliability.
Electric power systems are typically planned and operated to be capable of withstanding the most severe contingency that can occur on the system. In other words, the system must be able to suffer the most serious single contingency (often called the n-1 criterion) without overloads, low voltages, system instability, or loss of customer load. In some regions, the n-1 criterion may be defined to involve more than a single element – for example, loss of both transmission circuits that share a common set of towers, or a fault on the system not properly cleared because of a relay or circuit breaker malfunction. Whatever the case, system operators must deal with such contingencies in a minimum amount of time, and adjust generator outputs and system flows so that transmission line loadings and voltages are quickly returned to safe operating levels, and thereby be prepared for any subsequent contingency.
The events surrounding the August 14, 2003 Blackout emphasize the importance of having strong planning and operating criteria. There are some who argue that substantial transmission additions need to be made to improve the reliability of the bulk power system. While strengthening the system at strategic locations may be desirable, it must also be recognized that adding transmission reinforcements will also make the bulk power supply system electrically tighter; thus, any severe disturbance could have a larger geographic impact. For this reason, each proposed addition must be thoroughly tested in accordance with the applicable regional reliability criteria to assure that the impact of such additions will not have adverse effects elsewhere. Reliability is a function of the criteria used, not the amount of transmission in service.
Some are now claiming that existing standards are too strong, and unduly restrict commercial use of the transmission system. As a result, moves are underway to relax planning and operating criteria in order to allow the transmission system to carry higher transfers. While attractive on paper, such increases in capability would be illusory. The bulk power system’s vulnerability to widespread interruptions and blackouts would increase dramatically. Attempts to relax or “water down” existing standards are contrary to the public interest. If implemented, they would surely lead to degradation in power supply reliability – a condition contrary to the goal of the blackout investigation, and to the wishes of the people. .
A strong transmission system designed and operated in accordance with weakened criteria would be disastrous. Instead, a concerted effort should be undertaken to determine if existing reliability criteria should be strengthened. Such an effort would recognize the geo-electrical magnitude of today’s interconnected networks, and the increased complexities deregulation and restructuring have introduced in planning and operating North American power systems. Most important, reliability should be considered a higher priority than commercial use. Only through strong standards and careful engineering can unacceptable power failures like the August 14 Blackout be avoided in the future. |
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To participate in Pest activities contact: Jack Casazza |