By Rich Heidorn Jr.

FERC on Thursday called for reliability rules requiring generator owners and operators to winterize their units and provide their reliability coordinators (RCs) and balancing authorities (BAs) with information about their preparations.

The commission issued the directive as a result of a joint FERC-NERC investigation into the abnormal cold and higher-than-forecast demand that caused MISO and SPP to seek voluntary load reductions and nearly forced load shedding in MISO South on Jan. 17, 2018. (See FERC, NERC to Probe January Outages in MISO South.)

“Today’s report finds that, despite prior guidance from FERC and NERC, cold weather events continue to result in unplanned outages that imperil reliable system operations,” the regulators said in a press release. Although the system remained stable, “continued reliable operation would have required shedding firm load if MISO had experienced its largest single generation contingency in MISO South.”

They said the need for a new reliability standard to improve generator performance was demonstrated by the 2018 incident as well as the large-scale unplanned outages during the 2014 polar vortex and the 2011 Southwest cold weather event.

“Learning from near-miss events is extremely important,” Chairman Neil Chatterjee said in announcing the report at Thursday’s open meeting.

The report said the 2018 incident resulted from both gas supply shortages and a failure to properly winterize generation facilities. It made 13 recommendations, calling for improvements in generator performance, load forecasts, communication and planning.

9 States Affected

The event affected all or parts of nine states, including MISO South (Arkansas, eastern Texas, Louisiana and Mississippi); southeastern SPP (lower Kansas-Missouri border, the eastern half of Oklahoma, Arkansas, eastern Texas and Louisiana); the western portion of the Tennessee Valley Authority (western Tennessee, lower Missouri, northeastern Oklahoma, northern Mississippi and Alabama) and the western portion of the Southeastern Reliability Coordinator (SeRC)/Southern Co. footprint (southern Mississippi and Alabama).

MISO did not expect to have a problem meeting its South load on Jan. 17, based on anticipated generator availability and precautionary measures it took to increase projected reserves. But conditions worsened because of the “extraordinary” level of generation outages and derates.

The report found 183 generating units in the RC footprints of SPP, MISO, TVA and SeRC suffered an outage, derate or failure to start between Monday, Jan. 15, and Thursday, Jan. 19.

Including generation already derated or on planned or unplanned outages before Jan. 15, the four RCs had more than 30,000 MW of generation unavailable in the South-Central portions of their footprints by the Jan. 17 morning peak.

MISO South had as much as 17,000 MW of generation unavailable — all but 4,000 MW unplanned — including 57% of generation in Louisiana and 23.5% of that in Arkansas.

“Had MISO’s next single contingency generation outage in MISO South of 1,163 MW occurred, continued reliable [bulk electric system] operations would have depended on system operators shedding firm load promptly to prevent further degradation of BES conditions,” the report said.

Weather Impact

Generator owners and operators (GOs and GOPs) directly blamed 14% of the generator failures between Jan. 15 and 19 on the cold weather, citing frozen sensing lines, frozen equipment, frozen water lines, frozen valves, blade icing and low-temperature cutoff limits.

An additional 30% were indirectly linked to the weather, including fuel curtailments to gas-fired generators (16%) and mechanical causes related to cold weather (14%), such as freezing of gas purge valve and steam turbine intercept valves, drops in oil pressure, wet or frozen coal and the loss of feedwater.

The report recommended GOs and GOPs implement freeze protection measures, such as installing wind breaks on generating units and conducting regular maintenance, and inspection of other protections, such as heat tracing equipment and thermal insulation.

The investigators noted about 70% of the unplanned outages occurred in gas-fired units. They recommended requiring gas generators to inform their RCs and BAs whether they have firm gas supplies.

Ambient Temperature Ratings

The report also recommended better information sharing on the impact of ambient temperatures on generators and transmission lines.

It said GOs and GOPs should ensure the accuracy of generating units’ ambient temperature design specifications and share them with RCs and BAs.

All four of the RCs experienced transmission constraints, and MISO declared an energy emergency because it lacked enough reserves to balance generation and load in South. But the researchers said some system operating limits that became constraints were based on summer temperatures or static, year-round ratings, which understated the lines’ winter capabilities.

The report said SOLs and their associated equipment ratings should be based on “at a minimum, ambient temperature conditions that would be expected during high summer load and high winter load conditions, respectively.”

Power Transfers

The report also noted that increased electricity demand resulted in large power transfers, with MISO and SPP dispatching remote wind generation and SPP importing power over its HVDC ties with ERCOT. In addition, MISO’s regional directional transfer (RDT) from Midwest to South exceeded its contractual firm and non-firm limit of 3,000 MW, peaking at 4,331 MW about 6:30 a.m. CT.

“Although MISO exceeded the RDTL, and did not reduce the RDT below the 3,000-MW limit within 30 minutes as contemplated by the settlement agreement [with SPP and neighboring RCs], MISO operators communicated with adjacent RCs … that MISO would be exceeding the limit, and that if MISO’s RDT flows caused a system emergency for the adjacent RCs, MISO would take appropriate actions,” the report said.

The report also called for improvements to the joint Regional Transfer Operations Procedure that governs MISO’s use of the RDT. The recommendations included changes to clarify roles and timing and a requirement that affected entities declare an emergency before MISO sheds firm load to reduce the RDT.

The report also recommended that RCs consider the deliverability of reserves, noting that the constraints “caused reserves to be stranded from MISO South.”

It also said MISO should notify the other RCs when it is counting on the as-available, non-firm portion of the RDT to deliver reserves for MISO South.

Inaccurate Load Forecasts

The investigators gave good marks to the RCs’ system operators, saying their actions were “effective and timely.” But they said they were hampered by inaccurate load forecasts for MISO South. MISO’s five-day forecast for Jan. 17 underestimated load by about 6,000 MW (18.9%), and its three-day forecast was 1,900 MW low (6.1%). The report said MISO should work with its local BAs and adjacent RCs to improve its accuracy.

“While MISO and its neighbors worked together to maintain system reliability during the event, we recognize the opportunity to collaborate on changes that improve coordination during extreme events,” MISO spokeswoman Julie Munsell said Thursday. “We look forward to reviewing the findings and recommendations in the final report.”

Studies and Drills

Several of the recommendations concerned additional studies.

The report recommends studies that consider “stressed but realistic conditions,” noting that none of the RCs had anticipated the widespread transmission constraints on Jan. 17.

MISO and SPP should “jointly perform seasonal transfer studies and sensitivity analyses in which MISO and SPP model same-direction simultaneous transfers (e.g. north to south, south to north, west to east) to determine constrained facilities so that they can develop mitigation plans or other procedures for the operators,” it said.

It also said planning coordinators and transmission planners should jointly develop and study scenarios to prepare them for extreme weather. It said the studies should include removing generation units entirely to represent actual generation outages as opposed to scaling generating unit outputs.

The study team also recommended that MISO and other RCs perform:

• Voltage stability analyses in future constrained conditions and benchmark planning and operations models against actual events that stressed the system;
• Periodic impact studies to identify which elements in the adjacent RCs’ systems have the most impact on their own systems; and
• Drills to “execute load-shedding for maintaining reserves while at the same time alleviating severe transmission conditions.”