The Western Grid at a Turning Point: Why Harmonized EMT Modeling and IBR Performance Criteria Are Now Essential

The Western Interconnection is undergoing one of the most significant transformations in its history. The rapid expansion of inverter-based resources (IBRs), HVDC transmission systems, grid-forming controls, and large AI-driven data center loads has fundamentally altered system behavior.

Traditional steady-state and phasor-domain simulations are no longer sufficient to evaluate emerging stability risks.

Electromagnetic Transient (EMT) modeling is no longer a niche analytical tool  it is becoming a foundational requirement for maintaining Bulk Power System (BPS) reliability.



This article explores why harmonization of EMT modeling, screening methodologies, and performance testing is now critical for the West  and what a structured regional framework could look like.

Why EMT Modeling Has Become a Core Reliability Requirement

Several converging trends have made EMT analysis indispensable:

• High penetration of inverter-based resources (solar, wind, BESS)
• Increasingly weak grid conditions in certain regions
• Rapid deployment of HVDC transmission
• Growth of nonlinear and large dynamic loads
• Deployment of grid-forming inverter technology
• Complex control interactions across multiple converter-based assets

Unlike conventional synchronous machines, inverter-based resources operate through fast-acting control systems. These controllers interact with grid conditions in sub-cycle timeframes, creating dynamics that cannot be fully captured in positive-sequence models.

As a result:

• EMT analysis is increasingly required for interconnection studies
• Transfer path assessments now rely on time-domain simulations
• Grid-forming performance must be validated in EMT tools
• Large IBR clusters require detailed converter-level modeling

EMT capability is becoming a strategic competency for transmission planners and utilities.

The Fundamental Challenge: Model Quality and Lifecycle Governance

One of the most pressing issues in the Western Interconnection is not simply the need for EMT studies it is the quality and timing of the models used in those studies.

Common challenges include:

• Generic models that obscure actual controller behavior
• Late delivery of EMT models in the interconnection process
• Reverse-engineered models built only to pass specific tests
• Legacy sites operating without validated EMT models
• Inconsistent model acceptance criteria across utilities

These gaps create real risks:

• Interconnection study delays
• Expensive rework and restudies
• Unidentified control interactions
• Reliability vulnerabilities that only surface during operations

A recurring industry theme is clear:

Models must reflect as-left field conditions  not theoretical design assumptions.

That requires structured verification, transparency, and lifecycle governance.

EMT Screening: Not Every Project Requires EMT But Many Do

Not every interconnection project demands EMT analysis. However, screening methodologies must be technically robust and consistent.

Current approaches often include:

• Short Circuit Ratio (SCR) thresholds
• Impedance-based stability metrics
• Radiality considerations (N-x conditions)
• Proximity to HVDC systems
• Size of IBR clusters
• Penetration of grid-forming inverters

The issue is not whether screening should occur — it is how consistently it is applied.

Without alignment, developers face:

• Conflicting regional requirements
• Duplicate analytical efforts
• Increased engineering cost
• Extended project timelines

A structured, harmonized screening framework would allow the West to:

• Focus EMT resources on high-risk scenarios
• Reduce redundant custom analysis
• Provide predictability for developers
• Preserve reliability margins
  

Harmonization: The Most Urgent Need

Across the industry, one theme stands out above all others

Harmonization is no longer optional.

Without a coordinated framework, the Western Interconnection risks fragmentation:

• Different modeling requirements per utility
• Conflicting performance tests
• Varying documentation standards
• Divergent screening thresholds
• Misaligned model validation processes

This patchwork environment increases costs and introduces reliability risk.

A unified regional approach would provide:

• Consistent EMT model requirements
• Standardized verification procedures
• Defined screening triggers
• Clear performance conformity tests
• Transparent documentation expectations

The result would be:

• Shorter interconnection timelines
• Lower engineering costs
• Reduced restudy burden
• Improved BPS reliability
• Greater confidence in IBR performance
  

A Structured Regional Framework: A Practical Path Forward

One practical solution is the development of a formal regional technical criterion focused on EMT modeling and IBR performance expectations.

Such a framework would:

• Promote consistency across the Western Interconnection
• Support existing reliability standards
• Be developed collaboratively among stakeholders
• Undergo public comment and balloting
• Carry institutional weight
• Provide guidance without adding unnecessary compliance burdens

This type of structured document can align expectations without becoming an enforceable reliability standard.

It can address both:

• The “what”  required modeling and performance criteria
• The “how”  verification, screening, testing, and governance processes
  

What a Harmonized EMT Criterion Could Include

A comprehensive regional framework could define:

1. IBR EMT Model Submission Requirements

• Required control system detail
• Inclusion of protection functions
• Parameter transparency expectations
• Confidential handling provisions

2. Model Quality Verification

• Standardized test benches
• Time-domain disturbance simulations
• Performance conformity validation
• Field-data benchmarking

3. Screening Methodology

• SCR-based triggers
• Impedance metrics
• HVDC proximity rules
• Grid-forming penetration thresholds
• Cluster size thresholds

4. Lifecycle Governance

• As-left model validation
• Model update timelines
• Change management procedures
• Ongoing performance monitoring

5. Alignment With National Standards

• IEEE 2800 performance expectations
• Emerging NERC reliability requirements
• Consistency with other ISOs and RTOs where appropriate
  

Strategic Implications for Transmission Planners and Developers

The Western grid is at an inflection point.

If harmonization succeeds:

• Project uncertainty decreases
• Engineering duplication declines
• Reliability improves
• Interconnection queues accelerate
• Study workloads become manageable

If fragmentation persists:

• Study rework increases
• Engineering costs rise
• Model inconsistencies persist
• Reliability vulnerabilities accumulate
• Delays become systemic

The scale and complexity of EMT studies  particularly for large IBR clusters, AI load centers, and HVDC integration  demand regional alignment.

EMT capability is no longer a niche expertise. It is strategic infrastructure.

Raising the Floor for Reliability

The objective is not to burden developers.

It is not to restrict innovation.

It is to ensure that the pace of grid transformation does not exceed the industry’s ability to model, test, and validate performance.

A harmonized framework would:

• Raise the minimum standard for model quality
• Improve confidence in study results
• Reduce latent operational risks
• Support faster, safer interconnections

The Western Interconnection has the technical expertise and institutional structure to implement this approach.

The opportunity now is to move from discussion to structured alignment.

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