VALLEY FORGE, Pa. — The difference between the reserve measurements in PJM’s real-time security-constrained economic dispatch (SCED) engine and its emergency management system (EMS) has been shrinking since PJM implemented calculation changes. (See “Reserve Differences Explained,” PJM OC Briefs: Aug. 8, 2017.)
PJM’s Joe Ciabattoni presented a graph that measured the absolute error as a percentage as part of his executive operations report presented at a Sept. 12 Operating Committee meeting. Prior to July 11, when PJM removed a 2% “back off” in the EMS that assumes resources will achieve only 98% of their stated capability; the error was relatively flat at just over 9%. Since then, the difference has declined by about half a percentage point.
Stakeholders have expressed concern that SCED was not pricing shortages accurately because publicly available reserve data didn’t match LMP changes. PJM explained previously that the publicly available data is from the EMS, while the actual shortage pricing comes through SCED, which is confidential. The measurement differences, PJM argued, created the appearance that there were more shortages than actually existed.
With the small sample size, Ciabattoni hesitated to suggest the issue has been resolved.
“Even though these numbers have appeared to improve slightly, I think we need more time,” he said.
TOs to Receive Confidential Generation Data for System Restoration
PJM’s Dave Schweizer presented proposed Operating Agreement changes that would provide transmission owners with confidential data about generators that are part of the TOs’ system-failure restoration plan.
PJM currently provides such information when a unit is providing black start service or is modeled in the TO’s EMS plan. The information includes real-time unit status, real and reactive power, outage data and reactive capability. PJM proposes adding “system-restoration planning data,” such as unit start times, ramp rates, start-up loads and low-load operating capabilities.
The requested changes are in preparation for PJM’s request for proposals (RFP) on black start units coming in January. (See “Black Start RFP Process Offers Opportunity to Re-examine System Setup,” PJM OC Briefs.) GT Power Group’s Dave Pratzon asked if PJM would be able to identify where black start proposals would be “useful rather than just a shot in the dark,” citing costs of developing proposals for multiple potential sites as a deterrent for developing proposals that aren’t likely to be approved.
Schweizer said the RFP is for the entire RTO, so “we wouldn’t be able to reach out … and say, ‘you could put black start there’ because it’s an open process.”
He acknowledged staff continues to look for ways to make the process “less onerous.”
Gas-Pipeline Coordination Largely Confidential
PJM’s Ken Seiler said staff have been working with gas-pipeline operators for at least a year to increase gas-electric coordination, the results of which are expected to be rolled out over the next three years. Details are coming, he said, but specifics — such as which gas-fired units that are dual-fuel are connected to more than one pipeline — aren’t.
“There’s going to be a lot of things that we can share … in terms of megawatts and what pipelines they’re associated with that may be impacted, but we’re not going to get into specifics because we don’t want to identify any potential sensitivities that we have within the system,” he said.
The discussion came as part of PJM’s ongoing focus on system hardening and resilience.
“I think it will be great for people to get a feel for the extent of the types of research and operations improvement you make,” said Pratzon, who had made the initial inquiry.
Staff are currently reviewing a list of about 50 extreme event contingencies and expect to have the gas-related ones complete prior to the winter.
Synchrophasors Backup
PJM’s Ryan Nice provided an update on staff efforts to roll out synchrophasor technology, which takes high-speed, time-stamped measurements of phase angles, voltage and frequency. PJM is using the more precise information for advanced energy-management applications. (See “PJM Seeks to Tap Synchrophasors’ Potential,” PJM Operating Committee Briefs.)
Nice said he is particularly excited about system-wide heat maps for measurements such as voltage magnitude, voltage angle and frequency.
“A human being understands nothing more rapidly and more intuitively than a colored map,” he said. “It makes us more responsive to the state of the grid.”
Staff have had to address how the sheer volume of data that PJM needs to handle has overwhelmed software that has performed well for other grid operators. PJM is the “abnormally big kid in the daycare center, and we break all the toys,” he said.
PJM has begun a demonstration project that will run a linear state estimator using only synchrophasor data. The project will run into 2018, at which point PJM will have to decide whether to purchase the system.
If successful, the system could be an equivalent replacement for the current EMS state estimator without relying on the same systems and software.
“It’s a miniature EMS system. It can do a lot of the same things, maybe a little bit more [rudimentarily],” he said. “A vulnerability that would work on the EMS system would not work on the synchrophasor network.”
Eclipse Analysis
The August solar eclipse resulted in less reduction in solar output and more load reduction than expected. PJM planned for a loss of up to 2,500 MW in solar generation, but an analysis found it dropped by about 2,220 MW between 2 p.m. and 4 p.m. on Aug. 21.
Also unexpected was a 5,000 MW load decrease during that period. Staff believe that might have in part stemmed from a corresponding temperature drop of about 3 degrees Fahrenheit, but PJM’s hourly data is inconclusive. Staff also are investigating whether customer behavioral changes played a role, noting that the residential control-automation system Nest announced it received positive feedback when it solicited approval from customers to reduce air-conditioning demand during the eclipse. (See “Eclipse Hot Takes,” PJM Markets and Reliability Committee Briefs: Aug. 24, 2017.)
PJM’s Joe Mulhern acknowledged that PJM’s calculations for behind-the-meter solar arrays are estimates. Staff believe they have the information about 90% triangulated from a database that oversees solar renewable energy credits (SRECs), time and location estimates and other publicly available data.
The analysis will provide a historical basis to plan for the 2024 eclipse, which will likely have a greater impact on the RTO “based on the amount of solar in the queue,” Mulhern said.
— Rory D. Sweeney