The number of natural gas-fired generating units vulnerable to fuel quality issues related to unconventional gas resources and liquefied natural gas (LNG) "is relatively low, 3.6% of all existing capacity," according to the North American Electric Reliability Corp.'s (NERC) "2009/2010 Winter Reliability Assessment" of power resources.
However, for the New England subregion of the Northeast Power Coordinating Council (NPCC), more than 35.3% of existing capacity resources are potentially vulnerable to fuel composition changes, NERC said.
Due to the high level of gas-fired generation within New England's power generation fleet, ISO New England has been studying the potential reliability impacts related to natural gas fuel supplies, NERC noted. More than 25 studies have been performed by ISO New England to date due to a wide range of events occurring on the regional natural gas supply and transmission systems.
Over the last three years ISO New England has been monitoring the developments within the regional natural gas pipeline industry, as pipelines revise the gas quality sections of their tariffs in response to an upcoming influx of LNG that is regasified into the northeastern United States/Canadian natural gas pipelines. Although ISO New England has not specifically studied the impacts of variations within the natural gas stream on gas turbines equipped with low-nitrogen oxide (NOx) burners, other studies were performed that simulate the loss of regional gas-fired generation. This "end-effect" -- the temporary loss of gas-fired generation -- would be a similar byproduct or result of any natural gas fuel quality issue affecting regional gas-fired power generators, NERC said.
In the Florida Reliability Coordinating Council (FRCC), which has predominately gas-fired generation, the FERC Gas Tariff Gas Quality Provisions for natural gas in the Florida market area has strict specifications on gas composition, Wobbe Index, rate of change of the Wobbe Index, and the heat content. The FRCC has not experienced gas quality issues in the past year. This is attributed to compliance with the gas quality specifications outlined in the gas tariff and improved communication between generator operators and gas transporters.
The Electric Reliability Council of Texas region is not generally reliant on any single natural gas supply paths that would impact significant amounts of generating capacity.
In the Canadian Maritimes within the last year one event led to reduced output due to fuel quality issues. However, the Maritimes believes these events occur infrequently and do not raise any major reliability concerns in their subregion, NERC said.
In the Southeastern Electric Reliability Council some generating units have made provisions to switch between two gas pipeline systems, reducing the dependence on any single interstate or intrastate pipeline system. Moreover, the diversity of generating resources further reduces the region's risk, NERC said.
Generator operators within the Southwest Power Pool continually monitor natural gas heat content and conduct regular communications with natural gas suppliers. Coordination with natural gas suppliers ensures that unannounced disruptions will not occur, NERC said.
The 2009/2010 Winter Reliability Assessment is available at www.nerc.com.
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