The Substation Cortex: An Alternative Digital Substation Solution

Presented By:
Carlos J. Casablanca, PE
James T. Wolf, PE
Jason M. Byerly, PE
American Electric Power, Corp. (AEP)
TechCon 2020


Since the end of the 2000s, American Electric Power (AEP) has deployed and evaluated fiber optic-based digital substation technologies employing the International Electrotechnical Commission (IEC) 61850 standard defining communication protocols for intelligent electronic devices at electrical substations. The intent of these evaluations has been to learn about the technology and manufacturer capabilities, while also making a fair and unbiased comparison of this technology to traditional hard-wired copper protection and control installations using the latest microprocessor-based Intelligent Electronics Devices (IEDs). AEP’s deployments, including a 100% fiber-optic communication based distribution station put in-service in 2016, have given insights to the opportunities that can be seized by pushing the boundaries of available technology to re-evaluate traditionally accepted methods of practice.

In this report, AEP will outline its cross-cutting plans for its next fiber optic-based digital substation, which will attempt to merge existing commercially available technologies employing point to multi-point fiber optic-based communications and switched Ethernet substation communications, with the concept of Centralized Protection and Control (CPC), a concept that was explored and presented by an IEEE PES Power System Relaying Committee working group in 2015. AEP will outline the business drivers behind their proposed implementation, a high-level scope of work, expected capabilities for the technology, and anticipated hurdles and risks.

Ultimately, the purpose of this report is to trigger interest and discussion in our industry, among academia, traditional and non-traditional vendors, and utilities. There will be many design, implementation, and operational considerations that will come with a system like the one being proposed, and AEP hopes to learn and receive guidance from its industry peers as it moves forward.

About AEP

American Electric Power (AEP) is one of the largest electric energy companies in the United States, serving approximately 5.4 million customers in eleven different states across a service territory of over 200,000 square miles. Supported by a long history of innovation, AEP owns and operates the nation’s largest transmission network with over 40,000 miles of transmission lines across its service territory (American Electric Power, n.d.). It is through the lens of the largest transmission company in the U.S. that AEP seeks to explore new technologies and innovations in the area of multi-vendor integrated substation monitoring, analytics, protection, and control, to ultimately deliver performance, cost, and security enhancements for the benefit of its customers and the transmission grid.

AEP’s Experience with IEC 61850

For the last two decades, AEP has adopted a redundancy practice that utilizes a dual-vendor Intelligent Electronic Device (IED) approach to protection and control standards. This approach was originally adopted to include a layer of redundancy against common failure modes that could exist from reliance on a single IED vendor, as well as to provide options in the event of vendor supply chain issues. When one of the vendors (General Electric, part of AEP’s dual-vendor approach) developed their first merging unit technology in the 2000s, AEP saw an opportunity to explore a new technology that had the potential to radically change protection and control design and construction philosophy.

This is why AEP first worked with General Electric (GE) in 2007 to deploy an evaluation installation of a GE Multilin HardFiber Brick (GE Brick) merging unit at one of our 345-kV substations in Ohio. The goal of the installation was to verify the ability of the new fiber-based technology to digitize analog values and appropriately time-stamp them for protection purposes. The GE Brick merging units were installed in the substation yard in the circuit breaker’s mechanism cabinet to feed digital sampled values to the in-service relay panel of a single 345-kV transmission line.

Several lessons learned resulted from this initial installation. Performing the demonstration on a 345-kV transmission line meant that the number of events to evaluate the performance of the device would be low, leading to some frustration and the need for a substantial evaluation time period. Additionally, the trip circuit inputs for the circuit breaker on the subject transmission line were not wired to the trip output contacts of the GE Brick device, making it impossible to compare the trip times from the active system and the GE Brick system when events did occur. In spite of this, the demonstration did provide some insights on the possible cost savings that could result from exchanging copper instrumentation and control cables in a substation with digital fiber-optic communication systems.

In the interest of applying these lessons learned and thoroughly evaluating a promising technology, AEP worked again with GE to deploy an installation of a fully integrated protection system leveraging GE Brick technology on the distribution portion of one of its existing substations in Ohio in 2012. The installation covered two transformer zones of protection, two bus differential circuits, and eight distribution feeders, and was configured to work in parallel with the existing AEP standard (copper-based) protection system. Contacts from the merging units were wired-in at the circuit breakers to auxiliary relays to confirm that the trip times over the fiber connection were acceptable for protection purposes. Over 30 different events were captured by the system and evaluated to confirm its performance. Through this demonstration, AEP was able to build confidence in the digital signals supplied by the GE Brick merging units to the relays. The reviewed oscillography data confirmed that the GE Brick fiber-based system performed within one to two milliseconds of the in-service copper hard-wired protection system to clear fault events. AEP was also able to develop a higher level of confidence that an installation using this platform could provide cost savings from reduced materials and labor associated with traditional copper cabling. Having taken these lessons into consideration, this installation was later expanded to include equipment from Schweitzer Engineering Laboratories (SEL), which began offering similar products in an early stage of development. Finally, AEP was able to identify the test procedures that would be necessary to successfully commission a fully digitized protection system using this hybrid IEC-61850/Process Bus solution, without using specialized test equipment.

Culminating AEP’s exploration of fiber-based digital protection and control technology and applying all of the lessons learned to-date, AEP built and put in-service the first stand-alone fiber-based substation protection system in the U.S. in 2016 (Ball & Byerly, 2017). This system was designed and deployed as the sole-acting protection solution at AEP’s Flag City substation in Ohio, a 138-kV/12-kV distribution substation tapped to a 138-kV line that serves four distribution feeders through a single distribution transformer. This installation leverages the GE Brick technology in a point-to-multi point configuration, and to-date has operated up to the necessary expectations of relay reliability.

Business Drivers

Based on the trajectory and lessons learned from AEP’s experience with the fiber-based IEC 61850 merging unit technology, it would appear that a natural evolution for AEP would have been to standardize on a dual-vendor point-to-multi-point protection and control standard as a next step. However, since AEP first explored this technology in 2007, AEP’s drivers have significantly changed, having been heavily influenced by the state of the world and input from our stakeholders and the technical capabilities of the industry. Multiple factors have prompted AEP to re-think its long-term approach to substation monitoring, analytics, protection, and control. The drivers AEP is seeking to achieve include:

  • Vendor independence – Expanding the range of vendors that can be efficiently integrated into production and maintenance processes, to ultimately result in lower equipment costs through increased competition.
  • Interoperability – Simple and low changeover cost options to allow AEP to dynamically switch across vendor solutions without impacting its production and maintenance processes, avoiding proprietary communication interfaces whenever possible without affecting reliability.
  • Efficiency – Alternative ways to monitor, protect, and control substations that can result in: reducing the number of high-expense substation devices; a reduced substation footprint; and reduced time and costs for construction, commissioning, and maintenance.
  • Physical and Cyber Security – AEP is seeking a secure, resilient, and compliant SCADA network and protection and control system that are immune to faults within a single system or vendor, including security breaches of individual vendors by malicious third parties.
  • Reliability and Resiliency – By deploying new applications that leverage traditional and non-traditional sensing and information processing techniques, incipient system disturbances can be detected and prevented before they occur, to mitigate system events that require protection systems to act.

Recent Industry Developments

Over the past five years, significant technical advancements have shifted the realm of possibilities in our industry. Very high performance computing capabilities are now available from off-the-shelf hardware that allow for the calculation of grid measurements and statuses in microseconds (Myrda, 2019). Merging unit devices that perform the analog-to-digital conversion of grid measurements are commercially available from most, if not all, of our traditional vendors. The consolidation of protection and control logic for a multi-terminal substation into a single device has been explored (IEEE PES Power System Relaying Committee, 2015), and the possibility has been recognized for combining these technologies and capabilities to implement a software defined control system running virtual services (Hunt, Flynn, & Smith, 2019) in a single machine.

However, in spite of these technical possibilities, the present day pursuit and implementation of such a solution is currently not without its risks, requiring significant research and external funding (ARPA-E, n.d.) (New York Power Authority, 2019). Several efforts (IEEE PES Power System Relaying Committee, 2015) have been undertaken over the past few decades to achieve such a solution with mixed results. By the year 2023, AEP intends to build a new substation that is able to demonstrate the benefits and capabilities of such a centralized protection and control device that enables multi-vendor integrated substation monitoring, analytics, protection, and control, while also mitigating its development and deployment risks. AEP intends to create a real-world environment for collaboration and testing among traditional and non-traditional vendors, utilities, and academia, capable of accepting production hardware (including, but not limited to, merging units, protection platforms, and instrumentation equipment) from any vendor, and application algorithms from third parties via an open hardware and software platform.

Scope of Work

To be able to perform evaluations of forthcoming technology as AEP has previously done in active substation environments, AEP’s next proposed implementation will involve deploying digital substation equipment at a greenfield transmission facility. The deployed design will utilize merging unit technology in combination with traditional IED decision making relays (from two distinctly different vendors) that are presently offered, with the point-to-multi point communication topology in mind. Substation assets, (such as circuit breakers, transformers, and motor operators) which supply measured quantities or require control functions will be outfitted with merging units from the vendor factory, such that their on-site integration involves only power and communication connections. These merging units and associated traditional relays that are connected in the point-to-multi point system will act as dual, independent, active protection systems for the substation.

In parallel with the two traditional relaying systems, a third CPC-style system (affectionately codenamed as the “Substation Cortex”) shall be integrated in a non-active capacity. This initial deployment of a CPC in an active AEP facility will be utilized to create a benchmark comparison to the active traditional relaying, and to provide the ability to safely test the interoperable compatibility between different merging unit vendors without the risks of inadvertent operation. By deploying the system as non-active, AEP can also design provisions to safely exchange in-place merging units from different vendors to evaluate compatibility with the CPC system. In addition to the observations regarding hardware and network architecture, AEP intends to utilize all of the collected substation information to gain experience and build confidence with virtual relay and digital signal manipulation substation applications that will run in the CPC’s software environment.

It can be expected that there is an unquantifiable number of unknowns associated with the necessary specifications of un-designed technology, with the high expectations outlined for this effort. In order to accomplish the degree of flexibility required to perform live evaluations on new equipment, it is recognized that the substation infrastructure will need special considerations to be effective. The substation infrastructure will all be considered for necessary additional design margins for evaluating digital substation components as they continue to evolve. These can be defined as, but not limited to, fiber-optic cabling and terminations, control building panel space, AC/DC power circuits, yard cabinets with associated mounting space, instrument transformer stands, and physical equipment location considerations. The substation communications infrastructure shall also be designed so that AEP can develop active experience with a switched-Ethernet Process Bus version of the IEC 61850 standard alongside the two point-to-multi-point systems.

Expected Capabilities and Production Applications

As explained above, the proposed substation will employ the next iteration in AEP’s point-to-multi-point approach to fiber-based protection as the in-production primary and backup protection and control system, leveraging fiber-based protection and control products that follow AEP’s legacy dual-vendor approach. In addition, AEP will pursue the implementation of a CPC device – using off-the-shelf hardware to operate in parallel with the dual-vendor primary and backup protection, as shown in Figure 1 below.

Figure 1 - Proposed Digital Substation Connection Architecture

With this proposed configuration, AEP will have a flexible and open platform capable of allowing a variety of hardware and software applications to be developed, implemented, and evaluated against existing technology. This flexibility will also be demonstrated through the evaluation of multiple (more than two) and different types of merging units. The primary intent of the CPC device will be to act as an on-line performance evaluation tool for the point-to-multi-point in-production dual vendor implementation. In addition, a series of applications and analytics will be developed, tested, and built for the CPC device to gather performance metrics from all devices in the substation, and to identify and report any abnormalities via system health reporting metrics. Ultimately, this deployment is targeted at creating an opportunity to explore the power of modern computing technology in a substation environment where all the available sensory data is available to a single decision-making engine that can act in the best and most-informed interests of the grid’s reliability.

Provided below is a list of some of the proposed applications for the CPC device, along with their expected timeline to deployment:

  • Short-Term Applications (2023)
    • Automated performance evaluation, tracking, and reporting of the dual-vendor in-production protection and control system
    • Automated performance, evaluation, tracking, and reporting of the CPC device
    • Automated relay setting extraction, evaluation, and comparison to system of record
    • Circuit Breaker and DC Systems Asset Health monitoring, including performance-based maintenance triggers to eventually replace time-based activities

  • Mid-Term Applications (2024)
    • Real-time estimation and validation of substation voltage and current measurements
    • Real-time validation of relay protection setting coordination via independent analysis
    • Setting-less protection evaluation
    • Applications developed by internal and vendor companies to replicate otherwise proprietary protection/analytics algorithms on an open-source platform
    • Transformer Asset Health monitoring

  • Long-term Applications (2025)
    • Deployment, communication, and execution of virtual switching orders
    • CPC redundancy and cross-checking algorithms (with multiple CPCs deployed)
    • Remote end-to-end protection communication facilitation, including a non-tripping line-differential (87L) protection as a “third system in parallel with in-production line protection”
    • Replication of the local monitoring, analytics, protection, and control functions in a remote control center.

Anticipated Hurdles, Risks, and Questions to Explore

As we actively develop and pursue the scope of work and proposed applications mentioned above, we are well aware and mindful of the difficulty of what we are proposing to do. The purposes of this report and some of the items mentioned below are to trigger additional discussion and interest among our peers and partners, to invite engagement, and to raise the level of industry research, and development on this subject to actively address some of the obvious and non-obvious hurdles, risks, and questions that need to be explored and addressed for the successful implementation of a CPC device.

Listed below are some of these items that AEP plans to explore as part of its project:

  • Will traditional vendors cooperate with this endeavor, and be willing to develop more open hardware and software solutions to interface with it?
  • Is it time to revisit IEC 61850 standard to take advantage of industry lessons learned since the last revision?
  • Can present-day off the shelf hardware meet the needs of a CPC device?
  • What is the most appropriate software architecture for a CPC device, to have an open platform capable of accepting secure internally and externally developed applications?
  • How will the core axioms of protection philosophy change with full-substation diagnostic information available?
  • What truly is the definition of redundancy for CPC systems and the array of merging units and sensors that support their operation? Is there an opportunity to reduce or refine what sensors we need to achieve reliability?
  • How can traditional phasor-based protection settings be enhanced and complimented by the presence of additional information, such as linear-state estimated values and analog sensor data?
  • What are the observable performance aspects and associated risks/concessions that come from electing to use point-to-multi point versus Process Bus communications architectures?
  • What type of Human Machine Interface (HMI) is necessary for a CPC device?
  • What will it take to achieve remote-end compatibility for relay coordination between a CPC and legacy devices?
  • What tools and training will our maintenance and production engineers and technicians need to adapt to the capabilities and needs of a CPC device?
  • How should we as an industry support the development or refinement of reliability compliance standards that are well informed of the risks associated with this new technology?
  • What software development and evaluation strategies should be adopted to allow for secure application development by internal and external developers?
  • Should the end-to-end fiber paths from the substation yard to the control building be hardened further against human and non-human actors? If so, how?

Conclusion and Next Steps

As mentioned at the outset, AEP intends to build its next fiber optic-based digital substation, in a manner that will merge existing commercially available technologies employing point to multi-point fiber optic-based communications and switched Ethernet substation communications, with the concept of Centralized Protection and Control, to achieve multi-vendor integrated substation monitoring, analytics, protection, and control. The drivers behind this initiative, a high-level scope of work, expected applications for the implementation, and anticipated hurdles and risks that have been presented in this report reflect only the surface tension of the initiative laid before us. Ultimately, the purpose of this report is to trigger interest, discussion, and engagement in our industry, among academia, traditional and non-traditional vendors, and utilities. There will be many design, implementation, and operational considerations that will need to be addressed with the deployment of a system like the one being proposed. AEP hopes to learn and receive guidance from industry peers, and share what it learns and develops, as it moves forward.


  1. American Electric Power. (n.d.). About Us – AEP Facts. Retrieved from American Electric Power Web site: https://www.aep.com/about/facts
  2. ARPA-E. (n.d.). Resilient, Cyber Secure Centralized Substation Protection. Retrieved from ARPA-E Web site: https://arpa-e.energy.gov/?q=slick-sheet-project/resilient-cyber-secure-centralized-substation-protection
  3. Ball, D. R., & Byerly, J. M. (2017, March). Fiber: from the Whiteboard to the Station Yard. Protection, Automation & Control World. Retrieved from https://www.pacw.org/issue/march_2017_issue/fiber_and_process_bus/fiber_from_the_whiteboard_to_the_station_yard/complete_article/1.html
  4. Hunt, R., Flynn, B., & Smith, T. (2019, July/August). The Substation of the Future. IEEE Power and Energy Magazine – Moving Toward a Digital Solution.
  5. IEEE PES Power System Relaying Committee. (2015, December). Centralized Substation Protection and Control. Report of Working Group K15 of the Substation Protection Subcommittee.
  6. Myrda, P. (2019, September). New and Emerging Protection and Control Devices – Industry Progress and Recent Activity. Electric Power Research Institute (EPRI).
  7. New York Power Authority. (2019, March 20). NYPA Receives Funding for Groundbreaking Asset Protection Program. Retrieved from NY Power Authority Web site: https://nypa.gov/news/press-releases/2019/20190320-assetprotection

Join our email list

We use cookies to give you the best online experience. By using this website you agree with our cookie policy.