Dive Brief:

• Tight load conditions that pushed the ISO-New England grid to the brink on Labor Day were partially due to an unplanned outage at Exelon's Mystic Generating Station — the plant at the center of an ongoing federal debate over fuel security.

• Units at the 1,700 MW gas plant tripped offline when the power supply was interrupted to a liquefied natural gas (LNG) import facility that provides fuel for the plant, Exelon said in a statement. The interruption was caused by a power line fault, said Dan Dolan, president of the New England Power Generators Association.

• The Federal Energy Regulatory Commission (FERC) in July ordered ISO-NE to rewrite its market rules to boost revenue for plants like Mystic, which can store liquefied natural gas (LNG) onsite. Exelon has also asked FERC to approve cost recovery for the plant, which it says will go offline in the early 2020s without ratepayer support.

Dive Insight:

The outage at the Mystic plant, located in Boston, highlights the issues at stake in contentious debates over fuel security in New England and grid resilience at FERC.

On Sept. 3, ISO-NE implemented emergency operating procedures, purchasing power from neighboring regions and calling for voluntary conservation as real-time prices topped $2600/MWh.

ISO-NE said at the time that errors in its load forecast and unplanned outages caused the situation, but did not name a specific cause. Dolan said that conversations with companies in the market revealed Mystic was involved. 

"Through conversations with market participants it was clear that Mystic was knocked off the system by an outside transmission outage," Dolan said. "That certainly contributed to the issues, in addition to missing the load forecast."

After Utility Dive reported the outage, Exelon said a power line fault affecting the neighboring Distrigas LNG import facility was to blame.

"The Distrigas LNG terminal experienced a power supply interruption around 3:30 p.m. on Sept. 3rd that resulted in a rare and significant fuel pressure reduction to Mystic Generating Station," Exelon said in an emailed statement. "The loss of fuel pressure resulted in an automatic loss of power at Mystic [unit] 8 and partial loss of power at Mystic [unit] 9."

ISO-NE does not release outage information for individual plants and declined to comment on whether Mystic was involved.

"We don't identify resources that undergo forced outages, nor any financial charges or credits for any specific resource," spokesperson Marcia Blomberg said via email. "That's market-sensitive, confidential information."

Blomberg said there were no forced outages on the ISO-NE transmission system that day, but that distribution lines not overseen by the grid operator could have caused other issues.

"As I understand it, there were problems at one location on the sub-transmission system," she said. "The ISO doesn't operate the sub-transmission system and can't 'see' in real time what's happening on that system."

The Mystic outage is likely to give ammunition to critics of ongoing price reforms at ISO-NE and FERC that could benefit plants with onsite fuel supplies.

In May, the grid operator asked FERC for a waiver from its market rules to keep Mystic online with ratepayer support past 2022. The plant is essential not only for its generation capacity, ISO-NE said, but because it provides financial support for the Distrigas facility — the sole LNG import hub in New England.

FERC denied the request in July, directing Exelon to file a separate cost recovery proposal and telling ISO-NE to rewrite its capacity market rules to value "fuel security" — the ability to store fuel like LNG onsite.

The first round of comments in that fuel security proceeding were due Friday. In its filing earlier this month, ISO-NE proposed to treat fuel-secure plants like Mystic as "price takers" in wholesale auctions — not allowing them to set price — until the grid operator can complete its capacity market rewrite.

The issues at stake in the fuel security proceeding echo larger questions about grid resilience animating the swirling debate over coal and nuclear bailouts at the federal level.

Last year, the Department of Energy asked FERC to approve cost recovery for plants with onsite fuel supplies, widely seen as an effort to prop up uncompetitive coal and nuclear generators.

FERC rejected the request in January, but opened a broad proceeding on resilience — the ability to "bounce back" from outages — that still considers issues of fuel security.

A key argument from backers of Mystic and the DOE plan is that plants with onsite fuel supplies are more secure and resilient than those that must be fed by a pipeline. President Trump has weighed in on the debate, saying "you can blow up a pipeline," but coal is "indestructible." In June he directed DOE to design a bailout package outside of FERC.

Critics of the DOE proposal and the Mystic cost recovery waiver argue that onsite fuel supplies have little to do with system resilience. The vast majority of outages are caused by problems with the transmission and distribution system, they argue, so subsidizing plants with fuel onsite will do little to make the grid more secure.

An unplanned outage caused by a power line fault is likely to lend credence to those arguments, and not for the first time in ISO-NE. In January, right before FERC rejected the DOE bailout plan, Massachusetts' sole nuclear plant went offline due to a transmission issue, forcing the ISO to purchase emergency power from its neighbors.

Clarification: This post has been updated to amend a statement from Dan Dolan, president of NEPGA. Dolan originally said ISO-NE informed him of the Mystic outage at a meeting of the New England Power Pool (NEPOOL), but later said he misremembered the source of the information. Multiple NEPOOL members verified that ISO-NE did not address the Mystic outage by name in public. Prior to that, the original post was updated to reflect comment from Exelon.