Interconnecting Large Loads and Generation in New York

1. Why interconnection has become the critical path

For most of the last two decades, the hardest part of building a large electrical facility in New York was permitting, real estate, or financing. That has changed. Today, the single most common reason a large load or generation project slips its schedule is the interconnection queue. The grid is being asked to absorb an unprecedented wave of new demand — hyperscale and AI data centers, electrified industrial processes, hydrogen electrolyzers — at the same time it is integrating large volumes of inverter-based generation and storage. The New York Independent System Operator (NYISO) is the gatekeeper for the bulk of that activity, and its studies now sit squarely on the critical path.

The encouraging news is that the process is far more navigable than it first appears. The requirements are documented, the data formats are standardized, and the points where projects stall are predictable. A customer who understands the System Impact Study (SIS) workflow and who arrives with a clean, validated modeling package can move through the process months faster than one who treats data assembly as an afterthought. This whitepaper distills the governing NYISO procedures into a working guide, and flags the places where engineering rigor pays for itself.

Three documents, one process

NYISO Technical Bulletin 266 (Nov 2025) — the supplemental procedure for the Load interconnection System Impact Study.

NYISO Transmission Expansion and Interconnection (TEI) Manual (Manual 23, v4.3) — the governing manual whose Section 3.5 sets the Load interconnection procedure that TB-266 supplements.

Modeling Guideline for NYISO Interconnection Data (v10) — the detailed technical specification for the steady-state, short-circuit, and stability models every interconnection customer must submit.

2. The regulatory landscape: where the rules live

NYISO interconnection requirements are spread across several layers, and knowing which layer governs your project prevents a great deal of wasted effort. At the top is the NYISO Open Access Transmission Tariff (OATT) — the FERC-jurisdictional document that carries the binding rules. The interconnection procedures themselves were substantially rewritten in response to FERC Order No. 2023. On May 1, 2024, NYISO filed extensive revisions that established new Standard Interconnection Procedures in Attachment HH of the OATT, replacing the older Large Facility and Small Generator procedures previously found in Attachments S, X, and Z.

Below the tariff sit the NYISO manuals and technical bulletins, which translate tariff requirements into working procedure. The TEI Manual (Manual 23) is the principal interconnection manual. Importantly, while most of its Section 3 interconnection content no longer applies to projects entering the new Standard Interconnection Procedures, its Section 3.5 — Load Interconnection Procedures — continues to govern load projects. That is the hook that Technical Bulletin 266 hangs on: TB-266 supplements the existing tariff requirements in OATT Section 3.9 and the TEI Manual for the Load SIS, and NYISO has signaled that tariff changes to the Load interconnection process are being contemplated as part of a 2026 project initiative. In other words, the load process described today is current but explicitly transitional, and customers should expect refinement.

For generation, storage, and other resources entering a Cluster Study under Attachment HH, the Modeling Guideline for NYISO Interconnection Data is the controlling technical specification. It defines the exact files, software versions, naming conventions, and performance tests that a project model must satisfy. Although it is written for cluster-study generation customers, much of its modeling discipline — software versions, data formats, validation expectations — is exactly what load customers will be expected to mirror for their own SIS.

3. Does your project even fall under NYISO?

The first question is jurisdictional. Not every large load triggers a NYISO study. The NYISO Load interconnection procedures apply to load interconnections that are either greater than 10 MW connecting at a voltage level of 115 kV or above, or 80 MW or more connecting at a voltage level below 115 kV. This includes uprates to existing or previously planned load projects. Proposed load interconnections that fall outside those criteria are not subject to the NYISO procedures; instead they fall under the Transmission Owner's procedures.

Proposed load interconnections that fall outside those criteria are not subject to the NYISO procedures; instead they fall under the Transmission Owner's procedures.Two practical points follow. First, a project's voltage level and size should be confirmed early, because they determine whether you are dealing with NYISO at all. Second, the threshold captures uprates — so an expansion of an existing facility can pull the whole site into the NYISO process even if the original load did not. A prior phase that was studied under the Transmission Owner's process because it sat below the threshold may need to be disclosed and characterized when the cumulative load crosses the line.

4. What NYISO actually does in a Load SIS — and what it does not

It is essential to set expectations correctly. In the Load interconnection process, NYISO's role is narrow and specific: it determines the reliability impacts of the load project on the system through the System Impact Study. The Load SIS is informational and non-binding. Once the SIS is complete and the customer has paid for the technical study, NYISO's role in the load interconnection process concludes.



After that, the project does not stop — it shifts to the Connecting Transmission Owner (CTO). The customer may elect to proceed with the CTO on the facility studies and then enter into a two-party interconnection agreement. NYISO is not a party to interconnection agreements for load interconnections. This two-stage structure — NYISO for the reliability assessment, the CTO for facilities and the contract — is one of the most frequently misunderstood aspects of the load process, and it has direct scheduling consequences: the work does not end when the SIS report is issued.

NYISO may also identify potentially Affected Transmission Owners (ATOs) or Affected Systems. These parties can review project information, including the study base cases, and the SIS results will be reviewed with them if the study determines they are in fact affected by the load project. For a project near a system boundary, this can widen the circle of reviewers and should be anticipated in the schedule.

5. Before you file: preparation that de-risks the schedule

The most leverage a customer has over its own timeline is exercised before the request is ever submitted. NYISO and the TEI Manual both emphasize early coordination with the CTO. In that coordination the customer should accomplish two things: determine the proposed Point of Interconnection (POI), including the substation or transmission line name and voltage level; and discuss a preliminary plan for the local upgrades that will be required at the POI.

To have a Load Interconnection Request deemed complete, the customer must submit two items through the NYISO interconnection portal: a completed interconnection request form, and a project conceptual one-line showing the project up to the POI with the POI clearly labeled. Those two deliverables sound modest, but a vague or unlabeled one-line is a common reason a request is not deemed complete.

Access control matters too. All project contacts should obtain CEII (Critical Energy/Electric Infrastructure Information) access and, where required, execute the CTO's confidentiality agreement before the project scoping call. NYISO typically schedules that scoping call within about two weeks of determining the request is complete, and any attendee lacking CEII access and an executed confidentiality agreement will be asked to leave before power system information is discussed. The fix is simple but easy to forget: clear your whole technical team for CEII well ahead of the call.

5.1 Characterizing the load

Before the SIS scope is finalized, NYISO requires the customer to characterize the project in detail. This is not a formality; the characterization shapes how the load is modeled and which sensitivities are run. Required detail includes:

• Category and characteristics of the load. For example: data centers and other computational load (traditional, AI training or inference, or cryptocurrency mining); industrial loads (mining and mineral processing, metals and heavy manufacturing, semiconductor and electronics manufacturing, chemical and petrochemical processing, or oil and gas production); hydrogen production facilities; or other categories.

• Load flexibility. Whether the load would reduce output during peak load periods — for how long, how many times, and whether the customer is willing to participate in NYISO's Distributed Energy Resource program.

• Daily and seasonal load profile. How the load behaves across the day and across seasons.

• Existing or previously planned prior-phase load. Including load below the NYISO threshold that was previously studied under the CTO process.

• Phased in-service plans. Expected dates and the accompanying MW levels for each phase.

• Power flow, dynamics, and short circuit modeling data. Provided in the requested format (discussed in detail in Section 8).

Two NYISO forms support this stage and can be reviewed in advance: the Modeling Data Summary of NYISO Interconnection Data (a generic interconnection form, so some fields may not apply to a load project) and the Load Interconnection Data Request Form. NYISO recommends that the customer have at least one project contact who is fluent in power system analysis software — specifically Siemens PSS®E and ASPEN OneLiner™ — because the modeling deliverables are produced and validated in those tools.

5.2 The study agreement and the deposit

Two commercial milestones gate the start of the study. The customer must execute the System Impact Study Agreement (SISA) within 30 days of receipt, and must submit a $150,000 study deposit before the SIS begins. The deposit is a true-up, not a fixed price: if actual study costs at finalization are less than $150,000, the customer is reimbursed the difference; if they exceed it, the customer is billed the difference. Those costs can include NYISO's use of contractors or consultants and computation services, and costs the CTO incurs. Budgeting should therefore treat $150,000 as a floor with upside, not a cap.

6. Inside the study: base cases, bundling, and adverse impacts

6.1 How the base case is built



The base system representation for a Load SIS is a year-five representation as approved by the NYISO Operating Committee, consistent with a recent NYISO planning study such as the latest Short-Term Assessment of Reliability (STAR). In limited circumstances, NYISO may run sensitivities to the base case — for example, to include other load projects that do not meet the STAR inclusion rules, or to model other load projects at their full requested level — but only where those other projects are in close electrical proximity to the POI and are expected to contribute to the adverse reliability impacts identified in the study. The practical implication is that your project is not studied in isolation: nearby pending load is part of the picture when it could compound an impact.

6.2 Bundling related projects

Where appropriate, NYISO will model several projects in the same post-project case if the projects are moving forward in the same time frame and could cumulatively contribute to the same adverse reliability impacts. Bundling streamlines administrative tasks — scope development, stakeholder presentation, base case and study file development — and lets the incremental impact of each project be studied efficiently. Crucially, if the analysis identifies violations of Applicable Reliability Requirements, the SIS will still identify the individual contribution of each project. Bundling does not blur accountability; it just avoids studying the same neighborhood from scratch several times over.

6.3 When the study finds an adverse impact

If the SIS finds that the project as proposed would cause adverse reliability impacts, NYISO performs further analysis to identify alternatives that eliminate the impact. Those alternatives may include potential Network Upgrades or changes to the project itself, and consideration is given to the load ramp-up schedule — because an impact may appear before the project reaches its full requested load. Everything identified here is informational and non-binding. Importantly, the SIS does not provide good-faith cost-and-schedule estimates for those Network Upgrades; those are developed later, during the facility study with the CTO.

7. Timeline, transparency, and the steps after the SIS

Under the current process, NYISO gives a conservative estimate of nine months from the customer's study selection to SIS completion. That figure includes both administrative items and the technical studies, and NYISO is explicit that it is informational only. Real schedules vary widely depending on how quickly project modeling information is validated, when the study commences, the extent of any adverse reliability impacts, and the complexity of any required Network Upgrades. The lesson is consistent with everything above: the variable a customer can most influence is the speed and quality of data validation.

Once the SIS commences, the customer and applicable CTOs can track progress through the NYISO interconnection portal, which provides weekly updates and an interactive Gantt chart of high-level tasks against time. This visibility is genuinely useful for coordinating downstream activities — equipment procurement, CTO engagement, financing milestones.

After the SIS, the project must complete a facilities study and an interconnection agreement with the CTO before it can go in service. Customers should engage the CTO early to understand its facility study process. One subtlety deserves emphasis: the system representation used for the facility study may differ from the one used in the SIS, which can lead to differences in the Network Upgrades each study identifies. A clean SIS result is necessary but not sufficient — the facility study can still surface new details.

8. The modeling data package: where projects win or lose time

If there is a single theme across NYISO's guidance, it is that a complete, correctly formatted, validated model is the fastest path through the process. The Modeling Guideline for NYISO Interconnection Data spells out the package for cluster-study projects, and its discipline is the benchmark for the data a load customer must provide. A complete modeling data package has four parts: a one-line diagram, a steady-state model, a short-circuit model, and a dynamic (stability) model. Each has specific software-version and file-format requirements.

8.1 Steady-state modeling essentials

The steady-state model should be aggregated wherever possible, using the fewest equivalent buses and generators — ideally one equivalent generator per resource type. NYISO publishes a strict bus-naming convention (the customer leaves a placeholder cluster number, and NYISO fills it in) and reserves bus numbers 888000 through 888999 for the project, which NYISO renumbers when adding the project to the post-project case. A few rules trip up newcomers repeatedly:

• Implicit transformers inside a generator are not allowed; the GSU and PSU must be modeled explicitly, with Rtran and Xtran set to zero on the machine.

• Generator P and Q limits must reflect the actual operating point and meet the OATT power-factor requirement of +/- 0.95 — measured at the POI for synchronous resources, or at the PSU high side for inverter-based resources.

• Pgen in the submitted .idv should be set to zero; NYISO dispatches the project itself.

• Transformer impedances follow a defined base convention: GSU impedances on the nameplate MVA, PSU impedances on the self-cooled MVA rating.

8.2 Short-circuit modeling essentials

Short-circuit models are built in ASPEN OneLiner™. Inverter-based generators are modeled as a Voltage-Controlled Current Source (VCCS) injecting reactive current only; synchronous machines are modeled as conventional generation. Per the NYISO TEI Manual, loads and shunts are ignored in short circuit and are excluded from the model. NYISO publishes its exact ASPEN solution settings (subtransient generator impedance, prefault voltage from a linear network solution, enforce current limits, simulate converter-interfaced resources and VCCS, and so on). The acceptance check is concrete: the project model must inject fault current into single-phase, two-phase, and three-phase-to-ground faults at the POI, and must create no network anomalies.

8.3 Stability modeling and ride-through

Stability models must use PSS®E standard library models wherever possible; a user-written model is permitted only with documentation showing that no standard library model fits, and only from a model series already accepted by the MMWG. The stability package is where two of the most important grid-protection standards are enforced:

• NERC PRC-024 ride-through. Protection settings in the .dyr file are checked against the PRC-024 voltage and frequency “no-trip” zones. The settings must reflect the plant's actual intended protection — they must not simply mimic the minimum requirement. A relay that trips before the required minimum time sits inside the no-trip zone and is non-compliant.
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• CTO-specific requirements (e.g., LIPA / PSEG-LI). Some Transmission Owners impose stricter ride-through than PRC-024, with larger no-trip zones and additional dynamic requirements such as smooth reactive-current injection and a specified active-power recovery rate after a fault. Projects in those territories must meet the stricter standard.

Model usability is then proven with defined tests: a 20-second flat (no-fault) run that must hold steady within tight tolerances and trip no units, and a 9-cycle three-phase fault at the POI after which the system must remain stable, no unit may trip, and generator voltages must return to at least 0.9 per unit within five seconds of fault clearing. A model that fails these tests is sent back, and the clock keeps running.

Keentel's practical takeaways

Confirm jurisdiction first — voltage and MW determine whether NYISO or the CTO governs.

Treat the conceptual one-line and POI definition as gating deliverables, not formalities.

Clear the entire technical team for CEII before the scoping call.

Budget the $150,000 deposit as a floor; actual costs true up in both directions.

Build models to the exact software versions, naming conventions, and base conventions — version mismatches cause avoidable rejections.

Make protection settings reflect real plant design, and pre-test against PRC-024 and any CTO-specific ride-through before submission.

Plan for the post-SIS CTO phase from day one — the SIS is informational, and the binding agreement is with the CTO.

9. How Keentel Engineering helps

Keentel Engineering supports load and generation customers across the full interconnection lifecycle: jurisdictional screening and POI strategy, conceptual one-line and request-package preparation, load characterization and flexibility analysis, and the assembly and validation of steady-state, short-circuit, and stability models to NYISO's exact specifications. We pre-run the model usability and ride-through checks NYISO will run, so issues are caught before submission rather than mid-study. And because NYISO's role ends at the SIS, we help carry the project into the CTO facilities study and interconnection agreement with continuity of engineering and modeling. The objective is simple: keep interconnection off the critical path.

Frequently Asked Questions

The answers below summarize current NYISO procedure for the Load interconnection System Impact Study and the modeling-data expectations that accompany it. Procedures are subject to change — NYISO has indicated that tariff changes to the Load interconnection process are being contemplated as part of a 2026 initiative — so confirm specifics against the current OATT, TEI Manual, and applicable Technical Bulletins before relying on them for a live project.