By Chris O’Malley
MISO plans to unveil a plan next spring for monitoring and managing low-voltage facilities that can cause overloads on its transmission system.
The plan, which will focus on sub-100-kV lines, is in response to the Sept. 8, 2011, Southwest blackout that cut power to 5 million people in Arizona, Southern California and Baja California in Mexico.
Investigators found that the loss of a 500-kV transmission line owned by Arizona Public Service Co. increased power flows through lower voltage systems in parallel to significant transmission corridors, according to a 2012 report by the Federal Energy Regulatory Commission and North American Electric Reliability Corp.
“The flow redistributions, voltage deviations and resulting overloads had a ripple effect, as transformers, transmission lines and generating units tripped offline, initiating automatic load shedding throughout the region in a relatively short period of time,” the report said.
MISO said a transmission owner’s request that the ISO manage some of its low-voltage facilities also was a driver in the initiative.
MISO will identify low-voltage systems that impact the bulk-electric system and establish criteria to determine what it should monitor or manage. MISO would monitor the low-voltage elements by including them in models and tracking power flows against operating limits. It would include the most important low-voltage lines in its congestion management and transmission planning.
Under its current proposal, MISO would include in its N-1-1 contingency analyses an assessment “of BES elements that would potentially overload and trip facilities on the low-voltage system that would propagate back to BES” or that would cause the models to fail to solve, indicating possible system instability.
A low-voltage facility would be deemed to have an impact on the BES if the trip of low-voltage facilities causes an overload greater than 100% of the emergency rating on a BES element or results in an unsolved power flow, and the initial BES contingency has a 3% line outage distribution factor (LODF) on the low-voltage candidate facility.
The effort is not intended to broaden the definition of the BES, MISO spokeswoman Jennifer June Lay said. “This is considered a BES reliability issue that is part of the ongoing reliability services provided by MISO and would result in no additional services to be marketed.”
MISO said it is working with stakeholders to develop a final methodology. It said it will update assessments of the low-voltage systems every two or three years.
Asset owners would be able to examine results, validate findings and comment on solutions, such as whether existing mitigation is available to avoid overloads of a low-voltage facility.
The 2011 Southwest blackout proved pricey for utilities.
FERC has meted out at least three penalties so far, including a $12 million penalty announced last summer against the Imperial Irrigation District. The non-profit California utility violated four reliability standards for transmission operations and planning said to have undermined BES reliability, regulators charged. FERC also said IID fell short in coordinating operations planning with neighboring systems. FERC only collected $3 million from IID, as it ordered the utility to spend $9 million on reliability enhancements.
Yesterday, FERC announced a settlement with the Western Area Power Administration’s Desert Southwest Region, which it said had violated three reliability standards in the blackout. WAPA agreed to improvements, including the modeling of “critical external facilities and facilities operated below 100 kV that can impact system operating limits on its transmission system,” FERC said.