Recommended resources
The freely available resources this lesson will direct you to.
Hello. This course will take you from preparing ERCOT power-flow cases through PSS®E contingency analysis, generation and load capacity searches, and GIS-ready reporting. Before running a case, though, it is important to define what the result is meant to establish.
Today you will distinguish an investment-grade steady-state screen—analysis you can use to compare candidate sites and identify likely network constraints—from an official ERCOT interconnection study. The distinction matters whenever you report a number such as “maximum generation without an upgrade”: that number is meaningful only within the cases, operating assumptions, and checks that produced it.
What a steady-state screen can tell you
Suppose you propose a renewable plant at a transmission bus. You add its injection to a PSS®E case, specify how the rest of the system balances that injection, solve the power flow, and test relevant equipment outages. As injection increases, a line may exceed its applicable rating after a particular outage. You can then estimate the largest injection that passes your defined set of steady-state checks.
A load search asks a similar but distinct question: how much additional withdrawal can be served at a point under the chosen balancing and contingency assumptions? A BESS needs at least two operating views because discharging injects power and charging withdraws it.
This is valuable screening evidence. It can reveal which candidate locations deserve more investigation, which outages matter, and whether a proposed capacity appears sensitive to dispatch or planned transmission changes. But the result is conditional. For example, “180 MW passes” does not mean that the point has an unconditional 180 MW of available capacity. It means that 180 MW passed the specified model cases and tests, using the specified project representation and system response.
An investment-grade screen is not a separate ERCOT approval category. Here it means a screen rigorous enough to inform an investment decision with its uncertainty visible. Compared with a quick single-case calculation, it should have traceable case versions, documented assumptions, credible operating scenarios, a defensible outage and monitor scope, and results that another analyst can reproduce. Rigor improves the decision; it does not confer formal study status.
ERCOT’s own screening is a different activity
The April 1, 2023 ERCOT Planning Guide describes a Security Screening Study for a qualifying large-generator interconnection request. ERCOT conducts this study as part of its interconnection process. It uses power-flow and transfer studies to identify potential dispatch limitations, but the guide calls it a high-level review that generally includes initial assumptions. Its preliminary report addresses the proposed point of interconnection and MW amount; it does not commit ERCOT or a transmission service provider (TSP) to recommend or build transmission improvements.
Read the April 1, 2023 ERCOT Planning Guide to see how ERCOT describes the status and purpose of its own studies. This is an official-process description, not a template that automatically makes an independently run screen official.
In Section 5.3.1, “Security Screening Study” (pp. 5-12–5-13), start with the study purpose. Continue through the paragraph beginning “The Security Screening Study is a high-level review,” then read the report caveat. Notice both what ERCOT estimates and what it declines to promise. Then read the opening paragraph of Section 5.3.2, “Full Interconnection Study” (p. 5-13), from the FIS definition. Pay particular attention to the distinction between reliable interconnection and market deliverability.
There are thus three levels, not two:
| Activity | Who produces it | What its result means |
|---|---|---|
| Independent investment-grade screen | Your study team or its consultant | A decision-support estimate under disclosed assumptions; not an ERCOT finding |
| ERCOT Security Screening Study | ERCOT, within the applicable interconnection process | An official but preliminary indication of potential limitations and POI suitability |
| Full Interconnection Study (FIS) | Conducted through the formal process described in the Planning Guide | A broader assessment of reliability impacts and facilities needed for interconnection |
The table follows the cited provisions for large generators. Do not assume that a new transmission-level load or every BESS configuration follows the identical procedural path. Establish the applicable current process and requirements for the particular facility before calling its study an ERCOT interconnection study.
Why a passing AC contingency run is not a completed interconnection study
Steady-state contingency analysis is important within a formal FIS, not a substitute for the FIS. The Planning Guide calls for a steady-state study based on an approved Steady State Working Group (SSWG) case, with documented modifications. It also requires contingency analysis to identify system limitations that could prevent full generator output. The FIS extends beyond that calculation to other studies needed to establish reliability impacts and required facilities.
Continue in the same Planning Guide. These passages show why the provenance of a power-flow case matters, while placing contingency analysis inside a larger formal study.
In Section 5.3.2.4.1, “Steady-State Analysis” (p. 5-18), read the first paragraph from the case requirement and the next paragraph from the contingency requirement. Note the roles of the approved starting case, documented changes, and applicable criteria. Then go to Section 6.1, “Steady-State Model Development” (pp. 6-1–6-2). Read the opening paragraph from the model description. In paragraph (1)(d), note that certain off-cycle updates are supplied as PSS/E incremental change files. Focus on why “the case” must include its revision and updates, not merely a saved file name.
A solved AC power flow represents an operating condition. Contingency analysis tests how that modeled condition responds to specified outages, including whether monitored quantities such as flows and bus voltages meet the chosen checks. It does not, by itself, establish short-circuit duty, dynamic performance during faults, protection adequacy, or the detailed design and cost of interconnection facilities. Those questions can change whether a project is practical even when its steady-state screen passes.
The reverse is also important: a favorable interconnection study is not a guarantee of unconstrained commercial output. As the Planning Guide states, the FIS is not intended to determine market deliverability or ensure freedom from congestion-related curtailment. “Can be reliably interconnected under the applicable studies” and “can always sell full output without congestion” are different claims.
Give a capacity number its proper boundary
Imagine a candidate for which your screen finds that 150 MW passes and 170 MW fails: one studied outage overloads a nearby transformer at 170 MW. The justified conclusion is not simply “capacity is 150 MW.” It is closer to:
Screening result: Under the identified case revisions, dispatch and balancing assumptions, project model, monitored facilities, outage set, and thermal and voltage checks, 150 MW passed; 170 MW failed due to the identified transformer under the identified outage. The passing limit lies between those tested levels and requires refinement. This is not an ERCOT-approved interconnection capacity or a determination that no upgrades are required.
That wording preserves several distinctions:
- A tested bracket is not an exact maximum. Later lessons will refine the first failing range.
- A limiting facility is evidence, not yet an upgrade decision. Model validity, existing overloads, permissible adjustments, and other scenarios need review.
- “No upgrade identified” is narrower than “no upgrade required.” An unmodeled operating condition or another formal study may reveal a requirement.
- The direction matters. Generation injection, new load withdrawal, BESS charging, and BESS discharging need appropriately defined scenarios; one result should not be reused for another.
For a GIS platform, this boundary should travel with the mapped number. A candidate-point symbol labeled “150 MW” invites overinterpretation if the user cannot also retrieve its study status, case and revision, operating mode, scenario, limiting outage and facility, and assumptions. Keep an independent screen visibly separate from any subsequent official study finding. Protect access to underlying cases and project data according to their applicable permissions; a map is not a reason to make restricted information public.
Finally, treat the provided Planning Guide as a dated reference: it is the April 1, 2023 edition, not proof that every cited provision is current today. Before conducting or characterizing a live ERCOT study, verify the current governing documents and project-specific process.
Takeaway
Investment-grade steady-state screening can support a disciplined site comparison and a conditional estimate of injection or withdrawal capacity. ERCOT’s Security Screening Study is an official but preliminary process step for applicable requests; a formal FIS has a broader reliability and facilities scope. None of these should be described as a guarantee of unconstrained market output.
In the next lesson, you will turn this boundary into something operational: identifying the PSS®E case and supporting files needed so that a contingency result can be reproduced and its assumptions audited.