CAISO to Rely on New Emergency Measure to Ease Path 26 Transfers
CAISO said it will take advantage of a recently approved West-wide system reliability measure to ensure that its grid operators have the ability to send power into Southern California during instances when Aliso Canyon gas pipeline restrictions constrain output from regional gas-fired generation.
Peak Reliability — the West’s reliability coordinator — endorsed the new system operating limit (SOL) methodology, which provides Western Electricity Coordinating Council transmission operators the qualified ability to relax seasonal performance standards for “credible multiple contingencies” on a network under emergency conditions.
“That actually ends up meaning that, if we can technically justify it, we don’t have to hold to planning criteria in real-time operations,” Danny Johnson, CAISO senior operations engineer, said during a Dec. 7 market performance and planning forum.
The ISO will employ the new methodology to replace its previous authority to reserve transmission capacity on Path 26 — the major transmission link between the Southern California Edison and Pacific Gas and Electric service areas.
That authority was included in a raft of Aliso Canyon-related market provisions approved by FERC last spring, but the ISO asked to retire the authority this fall when it filed to extend most of the measures for a year beyond their original Nov. 30 sunset date. (See FERC OKs One-Year Extension for CAISO’s Alison Canyon Gas Rules.)
“Instead, we can use the Peak SOL methodology to increase transfer capability that the previous internal reservations gave us,” Johnson said.
Johnson explained that WECC path limits are established using “pre-contingency” power flow studies performed at the time that a path is identified or after an element along the path has undergone a significant change. Transmission paths are not re-evaluated on a regular basis, so SOLs do not account for minor changes in area load profiles or network topologies attributed to outages. The limits also fail to factor in real-time voltage conditions.
“We plan on using our real-time contingency analysis [RTCA] tool to monitor the actual elements that the path is trying to protect,” Johnson said. “This is more accurate because it’s not a pre-contingency proxy limit — it’s actual real-time data, built on voltage data. We’re able to reflect all of the neighboring topology changes either due to system changes or outages, which are constantly occurring,” allowing the ISO to observe a more accurate SOL in real time.
The RTCA tool also enables CAISO to incorporate the use of remedial action schemes — plans designed to automatically initiate corrective actions after detection of certain system conditions — to relieve congestion by strategically shedding load or generation to avoid overloading a line.
The ISO has determined that remedial action schemes (RAS) have “armed” an increasing amount of targeted SoCalEd load for shedding since the SOL for Path 26 was established in 2006.
“So in real time, if we assume that there’s additional load that will be dropped, that’s additional congestion relief that the RAS will provide,” Johnson said.
Use of the RTCA reduces the potential for Path 26 to hit its thermal limit, providing the ISO more latitude in exceeding the line’s 4,000-MW rating when Southern California gas restrictions hobble the region’s generators. The ISO estimates it could squeeze out a “few hundred” extra megawatts of transfer capability on the line under certain real-time conditions.
“We plan to use this only as a last-gasp emergency measure,” Johnson said. “By the time we use this, we will have exhausted all internal generation resources within Southern California, all demand response.”
Because the methodology requires use of real-time data, it cannot be incorporated into CAISO’s day-ahead market, which — along with the real-time market — will continue operating with the path’s current ratings from the ISO transmission register.
