NERC’s Revised PRC-024-3 Standard for Inverter-Based Generation Effective in October 2022

Inverter-based resources are being added to the power system at an increasing rate due to renewable energy mandates and clean energy goals. Because the current NERC standards were written long before this trend, many are being updated to ensure continued reliability and resilience under new and emerging conditions. Most notably, changes to PRC-024-3 in support of inverter-based generation performance are going into effect in October of this year. Interconnection programs and documentation procedures may need to be updated in order to maintain compliance.

Generation Losses Highlight Need for Change

From August 2016 to May 2018, there were numerous instances where renewable inverter-based generating resources performed inadequately after what should have been routine transmission system disturbances such as lighting strikes or trip and reclose situations. Power generation losses in these events varied from a low of 30 MW to a high of 1,200 MW, compounding reliability and resilience concerns.

New Requirements

PRC-024-3 has been changed to make clear that frequency and voltage protection shall be set such that generating resources do not trip or cease injecting current within the “no trip zone.”  There was ambiguity in the PRC-024-2 standard as to whether inverter-based resources could drop offline while in the “no trip zone” during fault clearing. The new, approved standard makes it clear that momentary cessation of inverter-based resources within the “no trip zone” are not acceptable and that these resources must not cease the injection of current during the time within this zone. The language in the standard was clarified so that that operation outside the “no trip zone” is a “may trip zone.” Inverter based generating resources are not obligated to trip during small excursions from the “no trip zone.” In the frequency and voltage data point tables, updates have been made to show that in some regions’ instantaneous trips are allowed, but the frequency calculations are made over a specific time and that instantaneous trip settings based on instantaneously calculated frequency measurements are not allowed.

The modified PRC-024-3 standard has four requirements:

• R1: Each Generator Owner (GO) shall set its applicable frequency protection, such that the applicable protection does not cause the generating resource to trip or cease injecting current within the “no trip zone”.
• R2: Each GO shall set its applicable voltage protection to not trip or cease injecting current in the “no trip zone”. A key point in R1 and R2 is that they do not mandate that company have these protection systems, only that if it does  have them, the settings must be compliant.
• R3: Each GO shall document each known equipment limitation that prevents resources with frequency or voltage protection from reaching the criteria in R1 or R2.
• R4: Settings shall be communicated with the Planning Coordinator or Transmission Planners upon request.

Next Steps

Generator Owners should carefully review their current compliance related evidence and interconnection process documents in advance of October 2022. Companies should be prepared to modify their interconnection review processes and NERC compliance program documents as necessary to maintain compliance.

With expertise in all areas of power system planning and power delivery, protection system engineering, TRC can provide independent project management services to review your company’s interconnection facilities review programs.

Resources

• NERC PRC-024-3 Redline to Last Approved
• NERC PRC-024-3 Standards Project Development Page
• NERC PRC-024 Implementation Plan
• TRC Protection and Controls Solutions
• TRC NERC Compliance Solutions

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