NYISO Interconnection Modeling Guidelines Explained: A Comprehensive Engineering Guide

Introduction

Interconnecting new generation, energy storage, and hybrid resources to the New York Independent System Operator (NYISO) transmission system requires rigorous power system modeling that meets strict technical and compliance standards. The NYISO Modeling Guideline for Interconnection Data (Version 10, July 1, 2024) establishes detailed requirements for steady-state, short-circuit, and dynamic stability models submitted as part of the NYISO Cluster Study process under Attachment HH of the NYISO Open Access Transmission Tariff (OATT) .

For project developers, inaccurate or incomplete modeling is one of the most common causes of study delays, deficiency notices, and re-submittals. For engineering firms, it requires deep familiarity not only with software tools such as PSS®E and ASPEN OneLiner, but also with NERC standards, NYISO-specific conventions, and Transmission Owner (TO) requirements.

This article provides a comprehensive, engineering-level explanation of NYISO interconnection modeling requirements, focusing on what is required, why it matters, and how projects can successfully navigate the NYISO cluster study process.

Purpose and Scope of the NYISO Modeling Guideline

The NYISO Modeling Guideline was developed to standardize the data, structure, and performance expectations for interconnection project models entering NYISO Cluster Studies, including Transitional Cluster Studies.

Core Objectives

• Ensure consistent and usable models across all interconnection requests
• Support accurate thermal, voltage, short-circuit, and stability analysis
• Reduce modeling ambiguity between Interconnection Customers, NYISO, and Connecting Transmission Owners (CTOs)

Modeling Deliverables Required

Each interconnection request must include:

1. One-line diagram
2. Steady-state (power flow) model
3. Short-circuit model
4. Dynamic (stability) model
5. Model usability testing compliance
   

One-Line Diagram Requirements

The one-line diagram is not a conceptual sketch—it is an engineering document that must accurately represent the project configuration.

Key requirements include:

• Professionally prepared engineering drawing
• Clear labeling of the Point of Interconnection (POI) using NYISO-recognized station or line names
• Representation of all major components:
• Generators or inverter blocks
• GSUs and PSUs
• Collector systems
• FACTS devices (STATCOM, SVC)
• HVDC components, if applicable

The one-line diagram must be fully consistent with all submitted models. Any mismatch is grounds for rejection.

Steady-State Modeling Requirements (PSS®E)

Steady-state models form the foundation of NYISO power flow analysis and must be compatible with PSS®E version 35.3.3 .

Aggregation Philosophy

NYISO strongly prefers aggregated modeling:

• One equivalent generator per resource type
• Separate equivalents only when technically necessary (e.g., different PSUs)

This reduces simulation complexity while preserving system behavior.

Bus Modeling and Naming Conventions

All project buses must:

• Use bus numbers 888000–888999
• Default voltage: 1.0 p.u.
• Default angle: 0 degrees
• Area, Owner, Zone set to 1

NYISO enforces strict bus naming conventions, such as:

• C####_POI
• C####_GSU1
• C####_PSU1
• C####_COL1
• C####_G1

These conventions allow NYISO to automatically integrate project models into Cluster Project Assessment (CPA) cases.

Generator Modeling Requirements

Control Modes

• Synchronous machines: Control mode 0
• Inverter-based resources (IBRs): Control mode 1 or 2, depending on reactive capability treatment

Reactive Capability

• Projects must meet ±0.95 power factor
• Measured at:
• POI for synchronous machines
• PSU high side for inverter-based resources

Active Power Settings

• Pgen set to 0 (NYISO dispatches generation)
• Pmax ≥ ERIS + losses
• Storage resources must properly represent both charging and discharging states
  

Transformer Modeling (GSU and PSU)

Transformers must be modeled explicitly—implicit transformers are not allowed.

Key requirements:

• Correct winding configuration (2- or 3-winding)
• Accurate R/X values on correct MVA base
• Proper tap changer settings and control modes
• Ratings must reflect nameplate or cooling stage, as applicable

Transformer errors are a frequent cause of NYISO model rejection.

Shunt Devices, STATCOMs, and SVCs

• Fixed and switched shunts must include realistic voltage control ranges
• STATCOMs are modeled as shunt FACTS devices in PSS®E
• SVCs are modeled as generators with zero real power capability

Voltage control buses must match between steady-state and dynamic models.

Short-Circuit Modeling Requirements (ASPEN OneLiner)

Short-circuit models must be compatible with ASPEN OneLiner version 15.7 .

General Principles

• Loads and shunts are excluded
• Synchronous generators modeled conventionally
• Inverter-based resources modeled as Voltage Controlled Current Sources (VCCS)

Fault Performance Expectations

The project must inject reactive current for:

• Single line-to-ground faults
• Line-to-line faults
• Three-phase faults

No network anomalies or non-convergence are permitted.

Transformer and Line Modeling

• Exact winding configurations and vector groups are mandatory
• Zero-sequence data must be explicitly defined
• Line impedances must include both positive and zero-sequence values

Incorrect grounding assumptions are a common modeling deficiency.

Stability Modeling Requirements (Dynamic Models)

Dynamic models must be compatible with PSS®E version 35.3.3 and rely on standard library models wherever possible .

Inverter-Based Resource Model Structure

A complete IBR dynamic model includes:

• Protection models (voltage and frequency)
• Generator model (e.g., REGCA1)
• Electrical control model (e.g., REECA1)
• Plant controller (e.g., REPCA1)
• Optional STATCOM or auxiliary controls

All protection must comply with NERC PRC-024 ride-through requirements.

Synchronous Resource Model Structure

Includes:

• Generator model
• Governor model
• Exciter model (simplified exciters discouraged)
• Stabilizer model
• Protection models

NYISO explicitly discourages oversimplified excitation systems.

Model Usability Testing

NYISO performs strict usability testing to confirm model reliability.

Required Tests

1. 20-second flat run test
2. 9-cycle three-phase fault test
3. Protection compliance verification
4. Primary frequency response and droop checks

Failure of any test results in model rejection.

Ride-Through and Recovery Performance

• No tripping during faults
• Active power recovery to ≥90%
• Voltage recovery to ≥0.9 p.u. within 5 seconds
• Compliance with NERC PRC-024 voltage and frequency curves

Transmission Owner–specific criteria (e.g., LIPA) may impose stricter limits.

Conclusion

NYISO interconnection modeling is not a formality—it is a highly technical engineering deliverable that directly impacts project schedules, costs, and feasibility. Successful projects require:

• Deep familiarity with NYISO conventions
• Accurate, consistent modeling across tools
• Compliance with NERC and TO-specific requirements
• Rigorous internal validation before submission

Engineering expertise and attention to detail are the difference between smooth cluster progression and months of costly delays.

25 Frequently Asked Questions (FAQs)