Loadability Studies Aid PRC-025-1 Compliance

Regulatory requirements governing Bulk Electric System (BES) power-generation owners and operators are expected to significantly increase the volume of work related to analyzing, implementing, and testing protective relays at sites.

While Bulk Electric System power-generation facilities have until 2019 to conform to the PRC-025-1 standard, early adopters can begin capturing a range of benefits now.

In August 2003, an electric power blackout across the northeast United States and Ontario, Canada, affected an estimated 50 million people. Analysis of this and other major disturbances over the past 25 years has revealed generators tripped for conditions that did not pose a direct risk to those units and associated equipment.

As a result, the North American Electric Reliability Corp. (NERC), Atlanta, created the PRC-025-1 Generator Relay Loadability Standard. According to Steve Nollette, supervising engineer for Emerson Network Power’s Electrical Reliability Services, Columbus, OH, the intent of the standard is to increase grid stability during system disturbances by reducing unnecessary tripping of generators or the number of “misoperations” caused by incorrect settings, logic, or design errors.

The Federal Energy Regulatory Commission (FERC), Washington, has launched a campaign designed to reduce misoperations by 25%, including implementation of standardized setting methodologies such as PRC-025-1, which is currently enforceable.

Bulk Electric System (BES) generation facilities, according to the NERC definition, are required to conform to PRC-025-1 by October 2019. Nollette explained that, while this seems like ample time, facilities should begin planning a loadability study now to reap the following benefits associated with early adoption and, thus, avoid the costly consequences of delay or noncompliance.

Better access to engineering resources. As regulatory requirements governing operations continue to change, single generation sites that operate with limited engineering resources may need assistance from external or outsourced resources such as contractors, who can perform the highly technical tasks needed to meet the new regulatory requirements. While multi-site generation entities often already utilize an engineering team specializing in matters pertaining to NERC compliance, they may also need assistance due to the volume of work related to analyzing, implementing, and testing all of their protective relays.

“The economic laws of supply and demand dictate that, as a deadline approaches and more generation plants rush to seek out contract assistance, the available supply of contractors and engineering firms will dwindle,” Nollette said. “This translates into higher costs and potentially lower quality. Early adopters will have access to greater engineering resources at lower costs.”

Less business interruption. For generation sites that have completed a system assessment and require changes to the load-sensitive protective relay settings, implementation and testing will need to be scheduled, requiring a maintenance outage. When a loadability study is performed earlier, there is a greater ability to schedule the implementation and testing during a planned outage rather than having to schedule a separate maintenance outage. Nollette explained that planned outages are typically part of a forecast and budget while unplanned maintenance outages typically incur additional unexpected costs and are disruptive to normal operations.

More time for special cases. In some instances, an existing relay system may not be capable of using the settings required by NERC PRC-025-1. In these special cases, the deadline for compliance is extended by two years to allow retrofit of the existing protective-relay system. As Nollette pointed out, this is a significant engineering effort that is best performed carefully, with sufficient time and resources. Early adopters will have the benefit of adequate time to plan, budget, engineer, remove, install, and test the new protective relays.

Planning, executing loadability studies

The complexity and amount of effort required to perform a generator loadability study, according to PRC-025-1, can vary widely depending upon system design, configuration, age, and documentation. Generation facilities should already be developing plans of action to meet the compliance deadline.

Start by determining if outside engineering help is needed. It’s likely that most generator owners (GOs) and generator operators (GOPs) already understand the make-up of their technical resources. Determining if external resources are needed to supplement compliance efforts could be as simple as not having enough staff for the number of facilities requiring assessment.

Determine the scope of your study. “Most engineers, facing PRC-025-1 compliance considerations for the first time, will need to exert significant time and effort to learn the new standard and how it applies to their site,” Nollette said. “To determine the scope of their efforts, GOs and GOPs need to evaluate which of their protective relays require analysis and how close they are to compliance.”

The first step in determining the scope is to gather generation-unit data, which will be used throughout the assessment process. Collecting this basic generation-unit information will provide a preview for the amount of work that will be needed. 

Nollette stated that required information can be found in the following documents: one-line drawings, three-line drawings, protective relay settings, relay test reports, and component nameplates.

Fig. 1. Typical synchronous generator protective-relay system. To help with determining how the standard applies to a given plant, the PRC-025-1 application guidelines illustrate a comprehensive protective relay scheme for a generation unit.

To help with determining how the standard applies to a given plant, the PRC-025-1 application guidelines illustrate a comprehensive protective-relay scheme for a generation unit. However, not all relays illustrated will necessarily exist in every system (see Fig. 1).

Once the generation system protective relays have been sorted into the appropriate options, as seen in Fig. 1, the remaining necessary information is gathered to assess each protective relay’s compliance. This information is also found within the documentation initially gathered for the generation unit data.

Table I. Comparison of Option A to Software Simulation

Understand the options available for compliance. NERC PRC-025-1 provides multiple options for setting load-responsive protective relays, as outlined in Attachment 1, Table I of the application guidelines. Each relay may have as many as three options available. Option A is the simplest to apply, but generally results in a less-accurate assessment. Software simulation, referred to as either Option B or Option C in the application guidelines, is more accurate because it models the machine’s reactive-power capability using field forcing simulations.

Compare nameplate data and relay settings with the PRC-025-1 standard to determine compliance. GOs must determine whether or not protective relays within the generation unit meet compliance requirements. The process of comparing as-found settings with the standard will require relay-specific information such as instrument transformer ratios and protective-relay pickup and/or tap values.

Start assessment process early and allot enough time for corrective actions. Whether determining the reactive power rating through conservative calculation (Option A) or through software simulation, corrective actions will likely need to be taken. Actions will include scheduling an outage for the implementation, testing, and documentation of the relay setting changes—all of which can take significant time to complete.

“No matter which compliance option is chosen, any changes to the existing settings should be carefully reviewed by the original-equipment manufacturer (OEM) and the protection engineers who are responsible for upstream coordination, prior to implementation,” Nollette said.

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.

According to Nollette, assimilating reporting characteristics that make the auditing process efficient will contribute to a successful audit with the Electrical Reliability Organization (ERO). Reporting methods that support a searchable document, a linked table of contents, bookmarking, and embedded links to supporting documentation should be an integral part of the demonstration report, Nollette explained.

Achieving NERC PRC-025-1 compliance requires a concerted effort. GOs or GOPs will need to rely heavily on either internal or external engineering resources, especially when moving beyond the conservative calculations used in Option A to more-accurate software simulations. While these simulations take more time to execute, they ultimately require fewer setting changes for better protection. Nollette concluded that a well-executed compliance plan rewards generating entities with a protected and more stable system and grid. 

Steve Nollette is a supervising engineer for Emerson Network Power, Electrical Reliability Services, Columbus, OH. He has more than 20 years of experience performing and managing electrical testing, maintenance, and engineering services.

EDITOR’S NOTE: To help facilities streamline the loadability study process, Emerson’s Electrical Reliability Services team has created a tool that automates the process of comparing settings with standard requirements. Download it at http://bit.ly/1Xqo4I6. For additional assistance, email NERCcompliance@Emerson.com or visit emersonnetwork.com.