NERC PRC-025: 2019 compliance starts now

Six steps to meet the new Generator Relay Loadability Standard.


Identifying the tasks to be completed during a maintenance outage can often start the day after startup from the last outage. This advanced planning is done to maximize ease of execution for better cost management, and ideally results in lower costs. The same can be said for compliance program management, so why wouldn’t you take a similar approach?

Not only are there many benefits to early adoption of regulatory standards, but non-compliance can mean substantial fines and penalties. In fact, the North American Electric Reliability Corporation (NERC) already has assessed fines as much as $500,000, depending on the violation, and the Federal Energy Regulatory Commission (FERC) can impose fines of up to $1 million per violation per day.

Yet, many facilities still fail to demonstrate compliance with the enforceable standards. Why? Most often, it’s because they lack awareness of a specific standard and its enforcement date. In some cases, the facility engineer in charge of understanding and applying NERC standards misinterprets the standard and believes it is not applicable to his or her facilities or underestimates the resources required to meet compliance.

If you are the owner or operator of a generation facility connected to the Bulk Electric System (BES), you need to start planning now to achieve compliance with NERC PRC-025 - Generator Relay Loadability Standard. Unlike many of the other NERC standards that have phased deadlines, PRC-025 requires compliance by October 2019. 

With less than 18 months to ensure compliance, you may need some help to fully understand the standard and how it applies it to your facility, especially if you lack internal resources dedicated to compliance program management. Additionally, you may need to budget and plan for needed system modification.

Understand the standard

PRC-025 is just one of the reliability standards created following the 2003 electric power blackout that impacted 50 million people in the United States and Canada. As the most widespread blackout in North American history, it is estimated to have cost between $7 billion and $14 billion. The event clearly exemplified the vulnerabilities of the BES and the need for regulation.

Post blackout analysis shows that generators had tripped for conditions that did not pose a direct risk to those generators and associated equipment.  This tripping expanded the scope and/or extended the duration of a disturbance unnecessarily. In fact, this very scenario contributed to the August 2003 blackout.

The purpose of the PRC-025 standard is to ensure that load-responsive protective relays associated with generation facilities are set at a level to prevent unnecessary tripping of generators during a system disturbance that does not pose a risk of damage to associated equipment. PRC-025 establishes criteria for setting load-responsive protective relays that permit load transfer from one generation site to the next, such that individual generators may supply the temporary reactive power demanded by load transients within their dynamic capability. Generator owners must apply the settings and provide evidence that the settings have been applied. Such evidence includes summaries of calculations, spreadsheets, simulation reports, and setting sheets. 

Streamline your assessment process

Figure 1. This example of a synchronous generator protective relay system is used in the application guidelines of PRC-025. Courtesy: VertivIf determining your system’s current level of compliance seems too labor intensive, not to worry. There is a proven procedure and support tool that can help streamline the process of assessing the settings for generation unit protection relays. Having this tool automates the manual application of the standard’s assessment criteria, thus reducing the time, effort, and energy needed to perform the assessment.

By working through the following six-step procedure and using the tool, GOs are better able to plan for the effort, time, and cost needed to meet PRC-025 requirements.

Step 1: Gather generation unit data 

Basic information should be collected prior to performing assessments of the relay settings. This generation unit information is used throughout the assessment process. Required information can be found in the following documents: one-line drawings, three-line drawings, protective relay settings, relay test reports, and component nameplates. Each document will contain key information such as the following:

  • Maximum rated megavolt amperes (MVA) for the generator
  • Rated power factor and voltage
  • Maximum MVA for generator step up (GSU) and unit auxiliary transformer, and associated impedances
  • Rated primary and secondary voltages at the set tap position for the GSU
  • Utility voltage
  • Megawatts (MW) reported to the transmission planning coordinator

Step 2: Determine which load-sensitive protective relays within the generation unit will require study for generator loadability

PRC-025 application guidelines illustrate an example protective relay scheme for a generation unit. This scheme is comprehensive in order to assist users in determining how the standard applies to a given plant. However, not all relays illustrated necessarily will exist in every system (see Figure 1).

Once the generation system protective relays have been sorted into the appropriate options as seen in Figure 1, the remaining protective device information is gathered to assess each protective relay’s compliance. This information also is found within the documentation gathered in Step 1.

Step 3: Populate each tab of the tool with data

Using the basic generation unit information gathered in Step 1, enter data into the nameplate tab of the assessment tool as shown in Figure 2. Continue this data entry on the corresponding tab for each protective relay identified in Step 2. 

This tool delivers a “compliant or not-compliant” assessment for each synchronous generator relay by comparing the protective relay settings with Option A of the standard, which derives the reactive power rating from conservative calculations. Additionally, the minimum settings required to become compliant with Option A also are calculated and presented. This gives the user valuable information indicating how close each load-sensitive relay setting is to Option A compliance.

Step 4: Decide whether to demonstrate compliance to the standard using Option A or using software simulation

Figure 2. The PRC-025 assessment tool has separate tabs that correspond with each relay that would be subject to the requirements of generator loadability. Courtesy: VertivIf choosing Option A, GOs will need to make necessary adjustments to protective relay settings and create the reporting necessary to demonstrate compliance. If GOs want to ensure more accurate relay settings that improve generating unit protection, they should investigate further through field-forcing. This allows GOs to model the machine’s reactive power capability during a transient sufficient enough to lower utility voltage to 85% of steady-state values. Once the approach has been decided, any changes to the existing settings should be carefully reviewed by the original equipment manufacturer (OEM) and the protection engineers responsible for upstream coordination prior to implementation.

Step 5: Perform corrective actions as needed

When an assessment tool reveals non-compliance, the next step is further evaluation and analysis conducted by trained technical experts. While the tools can reveal non-compliance for a particular relay setting, understanding the process of achieving compliance can be very technically demanding. 

For example, if the deviation from the required setting is not significant, it may be possible to use computer modeling and analysis to demonstrate compliance. But if the deviation is large, the relay setting change should be coordinated with transmission operators and other entities that can be affected. Corrective actions will include scheduling an outage for the implementation, testing, and documentation of the protective relays’ setting changes.

Step 6: Compile all information to complete the demonstration report

A thorough report for generator loadability will contain all information that was gathered during the assessment phase, supportive calculations from PRC-025-1 application guidelines, results from the software simulations (if performed), and documentation of any corrective actions and testing.

Assimilating reporting characteristics that make the auditing process efficient will contribute to a successful audit with the Electric Reliability Organization (ERO). Reporting methods that support a searchable document such as an electronic format employing optical character recognition (OCR) conversions, a linked table of contents, bookmarking, and embedded links to supportive documentation should be an integral part of the demonstration report. These attributes allow an auditor to quickly navigate the report to find critical information.

When reviewing reports, an auditor will be more likely to recognize formulas similar to those published in PRC-025 application guidelines, so all calculations should follow the guidelines as closely as practical. A high-level summary of all load-sensitive protective relays should be listed in a format to clearly show the reader which relays were studied as part of generator loadability and which were not applicable.

Act now for timely compliance

Achieving compliance with NERC reliability standards takes a concerted effort requiring ample time. But with the deadline for PRC-025 fast approaching, you may need to engage external experts. As demand for these specialized resources grows, qualified engineering talent become more scarce. 

Qualified engineering resources are able to assist GOs and GOPs with determining which compliance option detailed in PRC-025 is best suited for each application. 

Several factors should be considered such as how much time, effort, and expense is needed to achieve compliance. GOs and GOPs should also consider the risks associated with non-compliance such as fines and costly misoperation.

By choosing to start now, working with qualified engineering resources, and leveraging a quality assessment tool, you can simplify the compliance process. Additionally, you’ll be doing your part to better protect the grid while protecting your own operations.

Steve Nollette is supervising engineer for Emerson Network Power, Electrical Reliability Services (ERS). 


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