Ecmweb 8743 Generation Facilities 2
Ecmweb 8743 Generation Facilities 2
Ecmweb 8743 Generation Facilities 2
Ecmweb 8743 Generation Facilities 2
Ecmweb 8743 Generation Facilities 2

Making the Best Compliance Choice for Generation Facilities

Jan. 20, 2017
What it will take for facility owners to comply with the new NERC standard by October 2019, including the need to possibly hire outside engineering resources.

Many of you can recall the summer blackout of 2003, especially if you were among the 50 million people affected in parts of New York, Cleveland, and Detroit, as well as Toronto and Ottawa, Canada. During the event, 21 power plants shut down in just three minutes, stranding people in elevators and on trains, disrupting operations at hospitals and airports, interrupting water service, and generally causing havoc. In some places, the power stayed off for more than a day. In New York City alone, the estimated cost of the blackout was more than $500 million.

TomasSereda/iStock/Thinkstock

An analysis of this and other major disturbances over the last 25 years has revealed that during the events, generators tripped unnecessarily for conditions that did not pose a direct threat to those generators or other equipment. This nuisance tripping expanded the scope and duration of the disturbances.

In response, the North American Electric Reliability Corporation (NERC) created many reliability standards including PRC-025-1, Generator Relay Loadability, which applies to generating plants connected to the Bulk Electric System (BES). The standard requires plants to set load-responsive protective relays at a level to prevent unnecessary tripping of generators during a system disturbance. By reducing nuisance trips due to conservative overload protection settings, the standard will help increase stability of the BES and reduce the number of misoperations reported. At the same time, generation sites that comply with the standard can improve the performance and protection of their own equipment. They can prevent the costs and disruptions that result from nuisance tripping, thus achieving increased revenues as well as lower operational, maintenance, and repair costs.

Today, PRC-025-1 is enforceable, and generator owners are financially responsible for ensuring and demonstrating compliance by October 2019. While the deadline is still some years off, assessing compliance — and making any necessary system modifications in order to achieve compliance — is no small task for the owners and operators of these generators. Furthermore, their businesses may need to plan on investing considerable time and effort to meet these requirements — increasing the likelihood of hiring external engineering resources to assess compliance and begin developing a plan of action.

Understanding compliance options

PRC-025-1 outlines multiple options for setting load-responsive protective relays in order to achieve compliance with the new standard. In all cases, the process begins with assessing how load-sensitive relays currently perform. Generator owners and operators essentially have two options when it comes to performing this assessment. They can either derive reactive power rating from conservative calculations, or they can choose to use field-forcing simulations (electrical modeling software) to determine reactive power capabilities. The Table outlines the pros and cons of each scenario.

Deriving reactive power rating from conservative calculations — The first option for assessing compliance is the simplest to apply, but it generally results in a less accurate assessment. The standard applies to all load-sensitive relays in service during normal operations. It requires setting these relays greater than 115% of the calculated capacity of the machine. This calculated machine capacity is based upon 100% of the gross megawatt (MW) capability as reported to the transmission planner and the calculated reactive power capability of the machine. The calculated reactive power capability is derived from 150% of the MW value at rated megavolt amperes (MVA) and power factor (based on generator nameplate values).

Benefits and detriments of compliance options.

This option is relatively easy to execute once all system data is gathered and parsed. It allows the process of assessing compliance to be automated, which requires the least amount of effort to demonstrate compliance, if all settings comply. But that’s a big “if.”

Should some of the settings not comply, then the thresholds or pickup values of the load-sensitive protective relays typically need to be increased. Increasing settings in order to comply reduces system protection. In addition, changing settings requires coordination with upstream devices (including transmission) prior to implementation. This coordination effort may take as much or more time than simply performing the field-forcing simulations from the start. At minimum, implementing protective relay settings changes requires a maintenance outage and testing to comply with the most recent protection system maintenance and testing standards in NERC PRC-005.

In other words, generator owners and operators who choose this first option may still need to put considerable time and resources into the effort. And the results they achieve for that effort will not be as accurate or reliable as can be expected from field-forcing simulations. What’s more, there is a chance that the generation unit will not be capable of producing the calculated assumed reactive power output. In those cases, facilities will need to choose the alternative provided by the standard.

Field-forcing simulations to determine reactive power rating — To more accurately assess the reactive power capabilities of the generation unit, field-forcing simulations in purpose built software was created as an alternative method for assessing the compliance of protective relay settings. This option allows the generator owner, transmission owner, or distribution provider to simulate the output of a generating unit when the simple calculations are not adequate to achieve the desired protective relay setting.

On the positive side, field-forcing simulations provide a more accurate assessment of generator capability. Fully modeled machines are better protected, and the grid benefits from greater stability. Furthermore, in most cases, the majority of settings that fail with conservative calculations will pass the field-forcing simulation method. And, in some cases, all settings assessed are compliant, which eliminates the need to make any setting changes.

On the negative side, modeling software is expensive. Building an accurate model of the generation unit requires more engineering resources to collect data, build the model, run the simulations, and complete the assessments. For older machines and sites with poor document control and/or lack of original equipment manufacturer (OEM) support, complete system modeling becomes even more of a challenge.

Leveraging tools and support for assessing compliance

For the average single-site plant with limited engineering resources, the process of determining how close a system is to compliance can be quite a challenging task. Even for the multi-site owner with a dedicated NERC team, the task of analyzing tens, or even hundreds, of sites is a significant effort. Both single- and multi-site generation entities will likely require engineering assistance in order to complete the highly technical tasks necessary to meet the new regulatory requirements.

In addition, generation sites can benefit from using a quality assessment tool to automate tasks of the process and reduce the time, effort, and energy needed to accomplish those tasks. Engineering teams can create their own tools, or they may choose to take advantage of existing tools in the market.

Wherever a facility is in the process of achieving compliance, taking advantage of contract engineering support and using an assessment tool can help with planning the effort, time, and cost needed to meet the NERC standard’s requirements.

Advantages of early adoption

Though it can be tempting to wait for the compliance deadline to draw nearer, choosing to adopt the standard now makes sense for numerous reasons. First, the standard was designed to save effort, time, and expense associated with nuisance trips during system transients, and early adoption will maximize those benefits.

Generator owners and operators that act now may also enjoy easier access to quality engineering resources at a lower cost. As the deadline approaches and more facilities look to hire engineers, the laws of supply and demand could kick in, resulting in fewer available resources at higher costs.

Finally, if an assessment reveals that a facility must make changes to its load-sensitive protective relay settings, implementation and testing will need to be scheduled, requiring a maintenance outage. By performing the study earlier rather than later, it is more likely that implementation and testing can be scheduled during a planned outage as opposed to scheduling an unplanned maintenance outage, which typically costs more and can disrupt normal operations. In cases where the protective relay system must be retrofitted in order to achieve compliance, facilities that adopt early will benefit from more time to plan, budget, and install the new protective relays.

Weighing options

When it comes to PRC-025-1 compliance, owners have a number of choices to make, including when to adopt the standard and how to assess the compliance of the equipment’s existing protective relay system. Carefully considering the pros and cons of the two major reactive power capability assessment options — conservative calculations or field-forcing simulations — is important. Whatever approach is adopted, there are a few choices that can clearly benefit business. By choosing to adopt the standard early, working with a qualified engineering partner, and leveraging available assessment tools, the compliance process is greatly simplified. And facilities can feel good about doing their part to better protect the grid while still protecting operations.     

Nollette is a supervising engineer for Vertiv, Electrical Reliability Services (ERS), Westerville, Ohio. He can be reached at [email protected].

About the Author

Steve Nollette | Supervising Engineer

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