PSS®E Case and Support Files for Reproducible Contingency Studies

Hello. In this opening module, you will establish a trustworthy starting point for ERCOT steady-state studies before running outages or estimating how much generation or load a location can accommodate. This lesson answers a practical question: which files must you retain so that someone else can reproduce a contingency result, rather than merely view its final violation report?

Think of a proposed generator at a candidate bus. A reported overload depends not just on the bus and the generator’s MW output, but also on the particular grid case, updates applied to it, equipment selected for outage, facilities monitored, and PSS®E run settings. Identifying those inputs now will make later screening results useful for comparison and GIS handoff.

Start with the particular ERCOT case—not just “an ERCOT case”

The network model is the foundation. In a typical PSS®E workflow, the working power-flow case is a .sav saved case. It contains the modeled buses, equipment, operating conditions, and power-flow state. A single year may have multiple cases representing different seasons or load levels; releases and subsequent corrections matter too. Two analysts can therefore study the same candidate bus and obtain different results while both honestly saying they used an ERCOT case.

Read the following historical Planning Guide excerpts to see how ERCOT describes its case and contingency postings. This supplied PDF is not a check of current requirements: its reproduced sections carry different dates, and you will verify current documents later in the course.

For your own study, retain the original downloaded case package and record its exact filename, source posting, study year, season/load level, release or revision, and retrieval date. If the posting includes a PSS®E-formatted incremental change file, retain it separately and record whether, and in what order, it was applied. Do not silently overwrite the original .sav with an updated or project-modified case. Keep a working copy so you can distinguish what ERCOT supplied from what you changed.

A .raw file, if supplied, is another representation of power-flow network data; retain it as source material, but do not assume it is interchangeable with a saved, solved .sav for reproducing a run. A .sld single-line diagram can help you inspect the network visually. It is not required to calculate an ACCC result, and its drawing coordinates are not geographic coordinates for your GIS exports.

The files that tell ACCC what study to perform

Even with the correct case open, “run N-1” is underspecified. PSS®E’s AC Contingency Calculation (ACCC) workflow needs descriptions of where to look, what to check, and what to take out. This short demonstration uses a small teaching network and an older PSS®E interface; watch for the file roles, not menu locations or suggested numerical limits.

The three descriptions answer different questions:

These are study instructions, not results. For example, suppose an N-1 result shows no overload near a candidate site. Before interpreting that as available injection capacity, ask whether the relevant facilities were in the .mon and whether their credible outages were in the .con. You will build and audit these files in detail in later modules; for now, be able to recognize their roles and preserve the exact versions used.

ERCOT-posted contingency material is an important source for outage selection, but do not assume a posted file is automatically a ready-to-run .con for your case. Check its format, revision, case compatibility, and equipment identifiers. Likewise, a convenient automatically generated list is not proof that all events appropriate to an ERCOT study have been included. The video’s demonstration of selecting broad outage types illustrates a software capability, not a recommendation to generate every possible pair.

There is one more file commonly encountered in this ACCC workflow: the .dfx distribution-factor data file. PSS®E builds it using the case and the subsystem, monitor, and contingency descriptions. It is a derived analysis input used in the workflow, not a substitute for those source descriptions and not an AC violation report.

If you change the case or any of those three definitions, rebuild and check the .dfx for that study rather than relying on an old copy whose provenance is uncertain.

What constitutes a reproducible file package?

Imagine receiving only a spreadsheet of post-contingency overloads. You could inspect the numbers, but you could not establish whether they came from the intended seasonal case, whether an ERCOT update was applied, or whether the monitor omitted a nearby transformer. Reproducibility therefore requires both files and a record connecting them.

For one baseline run, assemble the following:

1. Source model: the unmodified case package, any associated incremental changes, and the identity of the exact case revision.
2. Working model: the .sav actually loaded for the run, with a record of changes from the source case. Later, these might include a candidate generator, BESS, or new load.
3. Study definitions: the exact .sub, .mon, and .con; identify the source and revision of any ERCOT contingency material used to prepare them.
4. Generated analysis input: the .dfx built for those definitions and that case.
5. Run evidence: PSS®E version, selected calculation settings and limits, build/run messages, and the resulting output files or reports. Preserve warnings as well as successful results.
6. Study assumptions: a written record of the scenario, applicable criteria documents and their revisions, and any dispatch or balancing changes needed to create it.

A simple inventory is enough at this stage. For every retained file, record its path, filename, purpose, source, revision or creation time, and whether it is original, modified, or generated. A file hash is helpful when similarly named copies circulate: it distinguishes byte-for-byte identical inputs from files that merely share a name. Keep restricted ERCOT source data and any derived outputs under the applicable access controls; a GIS-ready summary does not make its underlying model public.

Since you have PSS®E 34 and 35, also note which version opened and ran the case. Do not assume a case saved by one version can be opened or interpreted identically by the other. Preserve the original, use a working copy for conversion if needed, and document what you did. Later lessons will cover solving and validating that case; merely having a .sav filename is not evidence that its solved state is suitable.

Key takeaway

A reproducible contingency study has two layers: the identified network case and its updates, and the study instructions that define subsystems (.sub), monitoring (.mon), and outages (.con). The .dfx is generated from those inputs for the ACCC workflow. Retain run settings, messages, outputs, and a concise file inventory alongside them; otherwise, a plausible-looking capacity estimate may be impossible to audit.

Next, you will inspect an ERCOT case’s year, season, dispatch, topology, and revision information so you can decide whether the case you have is the case you intended to study.