MOD Standards
NERC MOD-026-2: Verification and Validation of Dynamic Models and Data
Expands model verification and validation responsibilities across all generating facility types, including a new EMT model requirement for inverter-based resources
What Is MOD-026-2?
MOD-026-2 consolidates and replaces the framework of MOD-026-1 and MOD-027-1, extending dynamic model verification requirements across all generating facility types connected to the bulk electric system. As the generating mix has shifted toward inverter-based resources, positive-sequence planning models alone have proven insufficient to represent how IBRs behave during grid disturbances. MOD-026-2 responds to that gap by adding a formal EMT model requirement for IBRs alongside the positive-sequence requirements that apply to all generator types.
Rather than prescribing uniform model specifications centrally, MOD-026-2 provides base model requirements and requires each Transmission Planner to develop and publish its own model requirements which Generator Owners must meet. Specific requirements a site must meet will therefore vary across the country.
The standard distinguishes between two methods of model development and assessment. Model verification demonstrates that site-specific parameters are representative of the actual facility, verifying configurable model parameters and equipment data and control system configuration are consistent to the extent possible. Model validation demonstrates that the model's dynamic performance during a voltage or frequency excursion matches recorded field behavior, either from a staged test or a captured system disturbance event.
Who Must Comply?
MOD-026-2 applies to Generator Owners of BES-connected generating facilities:
- Bulk Electric System synchronous generators and facilities meeting Inclusion I2 of the NERC BES definition
- Bulk Electric System IBR (solar, wind, BESS) resources
- Non-Bulk Electric System IBRs with a nameplate capacity greater than 20 MVA and connected at a voltage greater than 60 kV
The Transmission Planners's published model specifications under R1 define exactly what is required for your facility.
How MOD-026-2 Is Structured
MOD-026-2 organizes obligations across seven requirements. Not all requirements are applicable to all generator owners, so it is important to understand which apply to your facility type.
R1: Transmission Planner Publishes Model Requirements
The Transmission Planner must develop and publish its dynamic model requirements, which define the following:
- Positive-sequence model requirements, including which limiters and protection functions must be modeled
- For IBRs: identification of which legacy facilities require EMT models and the EMT model specifications
- Model acceptability criteria and documentation requirements to verify model performance, beyond what is specified in the standard
R2: Positive-Sequence Models (All Generators)
Generation Owners must provide positive-sequence dynamic models as specified by the Transmission Planner, verified and validated against field data and recorded system performance.
- Required models: generator, exciter, PSS, governor, and as specified by the Transmission Planner: OEL/UEL limiters and protection models
- Verification: site-specific parameters must be demonstrably representative of the actual facility
- Validation: model performance must match recorded field behavior during a voltage and frequency excursion event, from either a staged test or a captured system disturbance
R3: EMT Models (IBRs)
IBR Generator Owners must provide EMT models for facilities identified by the Transmission Planner. This is the most significant new obligation in MOD-026-2 relative to prior standards.
- Required models: IBRs, collector system, auxiliary control devices, plant controller, GSUs and MPTs, and all protective functions (AC and DC) and limiters
- OEM factory type tests or equivalent must be used to verify the individual IBR EMT model that the site model is built around. The EMT model large signal disturbances are compared to the positive-sequence model performance, as defined by the Transmission Planner
- Exclusions apply for legacy facilities where the OEM no longer supports EMT models, and for legacy facilities not identified by the Transmission Planner
R4: Updated Models After Changes
When relevant changes occur at the facility, updated models must be submitted to the Transmission Planner within 180 days, or within a mutually agreed timeframe.
- Triggers include: hardware changes, software updates, firmware changes, control mode changes, and setting changes
- Updated R2 positive-sequence models required for all generator types
- For IBRs, updated R3 EMT models are also required within the same timeframe
R5, R6: Transmission Planner Review and Response Cycle
The standard defines a formal review cycle with defined timelines for all parties.
- R5: the Transmission Planner must provide written acceptance or written rejection with supporting evidence within 120 days of receiving models
- R6 (rejection): if models are rejected, the Generator Owner must provide updated models or justification within 120 days, or a mutually agreeable timeframe
- R6 (Transmission Planner-initiated review): if the Transmission Planner requests a model review, the Generator Owner must respond within 180 days, or a mutually agreeable timeframe
R7: Requesting Existing Models from the Transmission Planner
Generator Owners should obtain the models currently in use for their facility from the Transmission Planner.
- The Transmission Planner must provide existing in-use models and accompanying documentation within 90 days of a written request
- This is a practical first step for any facility beginning a compliance effort — understanding what the Transmission Planner currently has on file avoids duplicating work already done
Common Compliance Challenges
Transmission Planner Requirements May Not Be Published Yet
MOD-026-2 requires Transmission Planners to develop and publish their model specifications, but not all Transmission Planners have completed this. Facilities should check with their Transmission Planner before beginning testing to confirm whether specifications are available. In some cases it may be appropriate to proceed with testing using the OEL, UEL, and protection model requirements likely to be required, rather than waiting.
EMT Model Development for IBRs
The R3 EMT model requirement is the most substantial new obligation in MOD-026-2. Required models cover not just the inverter but the full plant: collector system, plant controller, GSUs, and all protective functions including DC-side protection. Development requires PSCAD expertise and close coordination with the inverter manufacturer, particularly for real-code model sourcing and factory type test data.
Firmware Updates That Invalidate Existing Models
Under R4, firmware updates that modify the inverter or power plant controller response to a change in grid voltage or frequency or the facility response to system faults require re-evaluation of the facility's dynamic models and submittal of newly verified and validated models to the Transmission Planner. Similarly, changes to facility protection settings also require verification that protection models accurately reflect the new protection settings. This model evaluation must be completed within 180 days of the field changes being made. A change management process that flags model-relevant changes at the time they occur is essential for managing this ongoing requirement.
Generic Positive-Sequence Models That Don't Match Field Behavior
Generic IBR model families (REGC, REEC, REPC) are approximations. For facilities where actual inverter control behavior deviates significantly from the generic model structure, achieving a validated match within the Transmission Planner's acceptability criteria may require user-defined models or manufacturer-provided proprietary model files. This is where the distinction between model verification and validation matters practically.
Where to Start
For a facility beginning a MOD-026-2 compliance effort, the recommended sequence is:
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1
Request existing models from the Transmission Planner (R7). Find out what the Transmission Planner currently has on file for your facility before doing anything else.
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2
Download the Transmission Planner's published model specifications (R1). Confirm what models are required, what format, and what the acceptability criteria are. If specifications are not yet published, contact the Transmission Planner before proceeding.
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3
Identify required models. Determine which positive-sequence models are needed, and for IBR sites, whether the facility is identified for EMT model development and whether any legacy exclusions apply.
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4
Perform testing, develop missing models, and validate. Complete field testing for verification and validation, develop any models not already in place, and confirm the validated models meet the Transmission Planner's acceptability criteria.
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5
Submit models and documentation and track the 120-day response window under R5.
How TWC Can Help
TWC performs dynamic model verification and validation for both synchronous generators and IBRs, with significant experience with positive-sequence models, EMT simulation platforms, and working with regional entities and Transmission Planners to address model and data concerns.
Transmission Planner Requirements Review
We help you navigate your Transmission Planner's published specifications, identify which models apply to your facility, and flag any gaps between what you currently have and what is required.
Field Testing and Positive-Sequence Validation
We plan and execute staged field tests, develop or update positive-sequence models, and perform site performance to model comparison for R2 compliance. For IBRs, we work with manufacturer data and user-defined models where generic models are insufficient.
EMT Model Development and Validation
We develop and validate EMT models in PSCAD for R3 compliance, covering the full plant scope: inverter, collector system, plant controller, GSUs, and AC and DC protective functions. We also support clients in conversations with equipment manufacturers to secure correct models and ensure the models match the site and hardware configuration.
Submission and Ongoing Currency
We prepare model submissions in the format required by the applicable Transmission Planner and maintain compliance documentation covering the full verification and validation process. We also support change tracking under R4 so that firmware updates and equipment changes do not create unmanaged model re-verification and re-validation obligations.
Standards and References
- NERC MOD-026-2, Verification and Validation of Dynamic Models and Data — NERC Reliability Standards library
- NERC MOD-026-1 and MOD-027-1 — predecessor standards consolidated under MOD-026-2
Need Dynamic Model Verification?
Contact us to discuss your facility's MOD-026-2 requirements.
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