PRC-027 and Substation Relay Settings – No More "Set It" and "Forget It"

 By David G. Hart, Juergen Holbach, Saman Alaeddini, Ashok Gopalakrishnan

From electromechanical to microprocessor based relays, historically, the approach has been to “set and forget” the settings. While settings may have been reviewed with new system additions or upgrades, human resource demands and other priorities often limit system wide settings reviews. When new North American Electric Reliability Corporation (NERC) requirements take effect, utilities will be required to perform periodic reviews of their Bulk Electric System (BES) relay settings to ensure proper coordination.

These emerging requirements place additional workload on the utility protection team. To achieve compliance, utilities need to evaluate how the new requirements will impact their existing processes and how to strategically implement new processes and tools.

PRC-027 Overview

NERC PRC-027-1 is in the approval process and will require utilities to periodically review their protection system coordination for the BES. Requirements include: (i) Implement a process for developing new and revised settings, (ii) Periodic review of protection system coordination and settings, and (iii) to follow the process defined in (i) for new settings. In implementing a settings management process, the utility needs to look at the process for updating the short circuit model, the process for reviewing the protection settings, and the process for communicating coordination issues with neighboring utilities. The periodic review must be performed every 6 years by studying the results of a coordination study, reviewing the bus short circuit values for deviations exceeding 15 percent, or some combination of the two methods.

So what type of issues should a utility consider when deciding on how to implement a compliance process? Some suggestions are offered below.

Considerations in Looking at Implementation

Implementing these new requirements will impact the protection team in several areas. Some items that may need to be evaluated include:

• Merging of Protection Teams – Over the years, several utilities with separate protection teams, and therefore, distinct protection philosophies, have merged to create larger entities. In looking towards the future, the combined entity will have to work towards a unified protection philosophy, including a thorough review of the process to be followed for achieving system-wide BES protection coordination.
• Evolution of Existing Processes – As the number of studies and the need to document compliance increases, protection teams need to look for improved efficiency to deal with the increased workload. In addition to PRC-027, protection teams need to look at how this and other compliance requirements will impact their existing processes and the tools to implement those processes. Is it possible to consolidate processes, implement system standards that allows one to utilize new or different tools to facilitate automation of processes? How are short circuit, asset management for settings records, and other systems interfaced to reduce manual human errors? Do existing tools meet the new needs, and should other process consolidation and improvements be considered?
• Base Case – For BES systems, the base case has several major components: the short circuit model, the relay settings, and the coordination review. In looking at each of these components, some items to consider include:
  • Is my system primary model updated and correct?
  • Are the relay field settings the ones available for the coordination study?
  • What is the level of confidence in the system coordination in the base case?
The first two items are related to using accurate information and are associated with the process of updating the appropriate systems. The last item concerning coordination is obviously dependent on the first two, but even with completely accurate input data the overall BES system coordination should be considered in more detail. Over the years, coordination reviews are not usually performed over a wide area. Further, primary system and protection system contingencies are considered in a very limited manner, resulting in latent protection issues that need to be addressed prior to establishing the base case.
• Timeline – One of the major issues is to put a plan in place and start working on the overall implementation. As expected, it will take some time to conduct a review on how things are done today, create a plan for going forward, and implement the plan.

Obviously the implementation plan will also depend on these and other factors such as the utility budget, priorities, resources, and the size of the BES.

Getting Started

One of the major factors to consider is time. To review your existing processes and tools takes time and effort. Once completed, a plan can be created on how to move forward with new tools and processes to improve efficiency where needed. Depending on the system size, establishing a base case to review and update the system and relay data, as well as catch latent coordination issues requires not only to perform the studies but also to correct any discovered issues. In order to successfully meet these new workplace challenges and opportunities, getting a plan and timeline in place is the key.

For a downloadable copy of  July 2016 eNewsletter which includes this article, please visit the IEEE Smart Grid Resource Center.

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