| OMS # | Interface | Description | Curtailed MW | First start | Last end | Status |
|---|
This monitor tracks transmission congestion in the California ISO (CAISO) market using three official data feeds: shadow prices on CAISO's internal constraints (transmission lines, transformers, and operating nomograms), shadow prices on the scheduling constraints that govern the interties to neighboring grids, and transmission outage curtailments. All three come from CAISO's OASIS system and refresh automatically. There is no login, no paywall, and no modeled or estimated data — every number here comes from CAISO's own published market results.
When CAISO clears its market, it solves an optimization problem: serve forecast demand at the lowest total cost, subject to the physical limits of the transmission system. A shadow price is the mathematical byproduct of that optimization — for each constraint, it measures how much total system cost would change if that limit were relaxed by one megawatt. A constraint with a shadow price of zero is not limiting anything. A constraint with a large shadow price is binding: the grid is pushed up against that limit, and the market is paying real money to route around it. Shadow prices are the root cause behind locational marginal price (LMP) spreads — when you see a large price separation between two locations, a binding constraint with a significant shadow price is usually why.
The Internal tab shows congestion inside the CAISO footprint: individual transmission lines (branch constraints, shown as a line between two substations at a given voltage), transformer banks, multi-element operating nomograms, and constraints created by specific outages. This is where the largest shadow prices usually appear — a single loaded 70 kV or 115 kV line can clear at hundreds of dollars per megawatt-hour during a local peak.
The Interties tab shows scheduling constraints on the paths in and out of CAISO — the California–Oregon Intertie (COI/Malin), the Nevada–Oregon Border DC line, paths to the Desert Southwest, and others. These bind less often and at smaller magnitudes, but they move whole-system import economics when they do.
The sign is an accounting convention from the underlying optimization, not a market anomaly. In the convention CAISO uses for these reports, a negative value on a binding constraint means that adding one more megawatt of capability would reduce total system cost by that amount — a shadow price of −$15/MWh reads as “this limit is costing the system $15 for every megawatt it holds back.” Different constraint types carry different sign conventions, which is why this page ranks by magnitude: the absolute value is the primary severity signal, regardless of sign. The raw signed value is shown exactly as CAISO reports it.
The day-ahead market publishes an entire operating day at once, so a single DAM constraint has a different shadow price in every hour. This page shows the current hour's value as the headline number, with the day's peak and the hour it occurs shown alongside when the two differ meaningfully. That combination answers both questions a morning scan needs: what is binding right now, and how much worse does today get. Real-time (RTM) values are the most recent published interval.
Each intertie has an operating transfer capability (OTC), and when equipment is out for maintenance or forced out of service, that capability is curtailed. The outage table shows those curtailments in megawatts, sourced from CAISO's transmission outage feed and grouped by outage record. A 1,500 MW curtailment on a major path is a materially different event from a 20 MW one, so the table sorts by curtailed capacity. Long-duration limits — derates that persist for months or years rather than days — are separated into a standing path limitations section, so the operational outage view stays readable.
Congestion is one of the primary drivers of short-term electricity price behavior in CAISO. A binding internal branch reshapes local LMPs and can strand generation behind it; a multi-day curtailment on COI reshapes the supply stack across Northern California. Watching which constraints bind, at what shadow price, and which outages are scheduled over the coming weeks gives context for LMP spreads, congestion revenue right (CRR) positions, and day-ahead versus real-time divergence. The ranked list answers “what is binding right now and how badly,” and the outage log answers “what capability is offline and until when.”
Internal constraint shadow prices come from CAISO OASIS report PRC_NOMOGRAM; intertie scheduling constraint prices from PRC_CNSTR; outage and curtailment data from the OASIS transmission outage feed — all for both day-ahead and real-time markets. Data refreshes automatically, typically every 15–60 minutes. Constraint display names are parsed from CAISO's internal identifiers, so substation abbreviations reflect CAISO's naming rather than utility conventions. Map pins cover interties only; internal branch, transformer, and nomogram constraints are listed but not geocoded. Outage-to-constraint linkage is available where CAISO tags a constraint with an outage reference. This page is informational only and is not trading, financial, or operational advice.