- Modify the region outside the “No Trip” zone of the ride through curves so that registered entities do not interpret this area as a must trip zone.
- Clarify the “Off Nominal Frequency Capability Curve” and the “Curve Data Point” tables on pages 8 and 9 of PRC-024-2 to reconcile the 0.1 sec time delay in the frequency capability curve with the curve data point table that allows instantaneous operation.
- Clarify the language in point 5 of the Curve Details found in the Voltage Ride-Through Curve Clarifications to eliminate confusion about whether the curves pertain to RMS (Root Mean Square) or crest values.
- Remove inconsistency regarding per unit voltage and nominal operating voltage by correcting point 1 of the Curve Details found in the Voltage Ride-Through Curve Clarifications.
- Clarify the implied functionality of cumulative time by explicitly specifying the conditions for when cumulative values for low and high voltage curves start, stop, and reset.
- Clarify whether the voltage and frequency protection functions that can trip the inverter are subject to the standard’s requirements.
- Clarify the definition and whether the use of momentary cessation for inverter-based resources within the “No Trip” zone of PRC-024-2 is acceptable.
Renewable energy systems have dramatically changed the power generation resource mix. These new generation technologies no longer involve directly coupled rotating generators which were once standard in the industry. Now, inverters that change Direct Current (DC) electricity to the Alternating Current (AC) electricity suitable for delivery via AC transmission systems are becoming more prevalent, raising reliability concerns which NERC is addressing through modifications to its mandatory standards and compliance guidance.
NERC Standard PRC-024: Generator Frequency and Voltage Protective Relay Settings
On February 20, 2019 NERC approved a Standard Authorization Request (SAR) to initiate revisions to PRC-024 that address gaps related to inverter-based resources.
Depending on how long standard development takes, it is possible for the modified standard to become effective sometime in 2020, subject to FERC approval.
NERC Standard PRC-019: Coordination of Generating Unit or Plant Capabilities, Voltage Regulating Controls and Protection
Industry guidance is under development within NERC to address the application of PRC-019 considering inverter-based resources operating modes. The standard verifies coordination of generating unit facility voltage regulating controls, limit functions, equipment capabilities and protection system settings. The standard was developed based on traditional rotating generation technology and calls for a five-year cyclic review of voltage regulating system controls (including in-service limiters and protection functions) with the applicable equipment capabilities and the settings of the applicable protection system devices and functions.
When released, the PRC-019-2 Compliance Implementation Guidance will help develop a common understanding and identify methods for the coordination of voltage regulator controls, limit functions, and protective relay settings with respect to the standard. It will also establish reasonable assumptions for the calculations to meet the intent of the standard.
Next Steps
Utilities should stay informed regarding these two NERC initiatives to better understand and prepare for future compliance expectations.
Because your company may have limited technical resources in certain areas of planning and design, TRC can supplement your existing staff and programs, helping you develop internal initiatives to proactively respond to the changing demands of NERC compliance. Our experts provide assessment, corrective action and program implementation solutions for commissioning procedures, protection system design coordination with generating assets, including new renewable generating technology.
Resources
This regulatory update is a service to TRC’s utility clients, helping keep you informed of issues that impact your company’s electric system reliability and resilience risks along with related topics regarding future regulatory developments so you can achieve your business goals.
Inverter-Based Resources Gaps Whitepaper
Inverter-Based Resources Gaps Whitepaper Published December 20, 2018
PRC-024-2 Standard Modifications Project Development
Published
TRC NERC Compliance Services
Published
TRC Protection and Control Services
Published
