NERC PRC-019 Compliance: Engineering Coordination for Protection and Voltage Regulation

Introduction

The reliability of our electric grid depends on one crucial coordination — between voltage regulating systems and protection systems in generating facilities. To address vulnerabilities exposed during major events like the 2003 Northeast blackout, the North American Electric Reliability Corporation (NERC) introduced PRC-019, a critical standard focused on preventing unnecessary generator trips and ensuring grid stability.

At Keentel Engineering, we specialize in providing utility-grade PRC-019 compliance support for both synchronous generators and asynchronous/DG units. Our engineering team applies field-proven methodologies, coordination plots, and standards-based analysis to help generator owners and developers meet PRC-019 requirements with clarity and confidence.

In this guide, we break down the full PRC-019 compliance process—including data collection, curve plotting, RSAW documentation, and unique challenges encountered with modern renewable assets and legacy generators.

What is NERC PRC-019?

NERC PRC-019-2 is a reliability standard developed by the North American Electric Reliability Corporation (NERC) to verify proper coordination between three critical components within generating facilities:

• Voltage regulating system controls (such as Automatic Voltage Regulators [AVRs], limiters)
• Protection system devices (like relays and trips)
• Equipment capabilities (including generator thermal and excitation limits)
  

The goal is to ensure that generators, synchronous condensers, or other applicable assets can withstand system disturbances without tripping unnecessarily — a key factor in preventing cascading failures during grid instability events.

Who Must Comply?

NERC PRC-019 applies to facilities and resources that meet any of the following criteria:

• Synchronous generators with a nameplate rating > 20 MVA
• Synchronous condensers > 20 MVA
• Aggregated solar, wind, or BESS resources > 75 MVA
• Black start generators
• Distributed Energy Resources (DERs) that regulate voltage at the individual unit level

PRC-019 Requirements: R1 and R2

Requirement R1 – Five-Year Coordination Review

• R1.1.1: Limiters (such as OELs or UELs) must activate before protection relays trip the unit.
• R1.1.2: Protection devices must isolate equipment before damage can occur based on manufacturer-defined limits.

Requirement R2 – Change-Based Resubmission

Compliance assessments must be re-performed and submitted within 90 days of any changes to:

• AVR settings
• Protection schemes
• Related equipment upgrades
  

PRC-019 for Synchronous Generators

1. Data Collection

Key technical data required for study includes:

• Generator capability curves (P-Q, R-X)
• Settings for UELs, OELs, volts/hertz relays
• One-line and three-line diagrams
• Manufacturer protection and excitation settings reports

2. Plotting & Engineering Analysis

Engineers use tools such as Excel, PSSE, or DigSilent to overlay protection and limiter thresholds on:

• P-Q capability plots
• R-X diagrams
• Inverse time-current curves

For example, a non-compliant case would show a limiter curve falling below the machine’s stable operating region — risking unnecessary tripping.

3. Workflow Process

• Request and collect data via RFI (Request for Information)
• Perform visual and numerical evaluations
• Generate compliance plots and submit RSAW documentation

4. Common Study Challenges

• Lack of digital documentation for legacy units
• Faded or incomplete nameplate information
• Proprietary OEM data restrictions

PRC-019 Compliance for Asynchronous and Distributed Generation (Wind, Solar, BESS)

When dealing with Distributed Energy Resources (DERs) such as wind farms, solar PV, or battery storage, PRC-019 compliance becomes significantly more complex than traditional synchronous generator studies.

1. Understanding DER Complexity

Unlike single synchronous units, DER facilities often consist of dozens—or even hundreds—of smaller generators, each with its own controls, protection logic, and coordination challenges. For example, a wind farm with multiple Type III turbines may exhibit variations in overcurrent thresholds, limiter logic, and VAR control based on inverter design and firmware versions.

2. Study Phases for PRC-019 DER Compliance

Keentel’s DER-specific approach to PRC-019 compliance includes three critical phases:

Phase 1: Individual Generator Analysis

• Create TCC (Time-Current Characteristic) plots for each unit.
• Compare limiter thresholds (both normal and emergency modes) to associated overcurrent protection relays.
• Confirm coordination between fast-acting limiters and slow relays.

Phase 2: System-Level Coordination

• Evaluate feeder-level limits by aggregating all WTGs (Wind Turbine Generators).
• Determine collector bus capacity as the sum of WTG output and VAR compensator capacity.
• Ensure that all protective elements operate above the aggregated output thresholds.

Phase 3: Plant-Level Control Review

• Assess the performance and response of plant-level voltage regulation and power factor control schemes (including SCADA-driven STATCOMs, DVARs).
• Confirm that trip settings and limiter thresholds support grid stability and avoid unintentional islanding or disconnections.

Example: Voltage coordination diagrams for a STATCOM-based DVAR system show interactions between slow/fast control zones, undervoltage lockouts, and relay trips—each of which must be considered in the PRC-019 analysis.

Reporting and Documentation

Keentel delivers detailed, audit-ready PRC-019 reports that include:

• P-Q and TCC plots (capability vs. protection curves)
• Comparison tables between limiter thresholds and protection settings
• OEM data packages, including excitation control specs and thermal ratings
• IEEE/ANSI-based thermal curve calculations (e.g., ANSI C50.13)
• Coordination summary tables with clear pass/fail criteria

Common Challenges in DER Compliance Studies

Data Availability

• Older systems may lack digital settings or OEM test reports.
• In such cases, Keentel engineers reconstruct curves using reference materials like Electric Machinery Fundamentals.

Unfamiliar Data Formats

• Some OEMs provide volts-per-hertz or inverter trip curves in non-standard formats.
• Engineers must normalize and reinterpret these into verifiable coordination plots.

Regulatory Interpretation Variability

• Different Regional Entities or RCs (e.g., WECC, NPCC) may interpret PRC-019 requirements differently.
• Proper documentation and detailed technical justifications are critical to pass audits without penalties.

The Keentel Engineering PRC-019 Solution

At Keentel Engineering, we take the burden off your compliance team:

1. Full-scope PRC-019 studies for both synchronous and inverter-based systems
2. Collaboration with OEMs for accessing protected control data
3. High-precision curve plotting with PSSE, DIgSILENT, and MATLAB
4. Complete RSAW documentation tailored for NERC audit readiness
5. Post-audit support, ongoing updates, and engineering advisory services

Conclusion: PRC-019 Is More Than Compliance

PRC-019 isn’t just about ticking off a regulatory box — it’s about operational reliability. Whether you're managing a 50-year-old hydroelectric generator or a modern solar farm with inverter-based resources, verifying proper coordination between voltage regulation and protection ensures uptime, safety, and system integrity.

Let Keentel Engineering help you transform PRC-019 from a risk into a reliability asset. With technical rigor and regulatory experience, we ensure your grid-connected facilities meet the highest standards of performance and compliance.

FAQs on NERC PRC-019