Centralizing protection

Centralizing protection

Combining the functions of multiple relays into one device, CPC reduces network complexity, thus providing the means to better manage substation protection. And, by offering CPC as a virtualized image, ABB enhances scalability and flexibility – a boon for time-critical control and protection applications.

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Jani Valtari ABB Electrification, Tampere, Finland, jani.valtari@fi.abb.com

By necessity governmental targets for achieving carbon neutrality are ambitious; some countries are even aiming to meet their targets by 2035. Thus, change needs to happen rapidely. Electrical energy plays a significant role, as it can be produced and distributed with a low carbon footprint.

Nonetheless, with the increasing penetration of renewable energy and the advent of wide-scale adoption of battery energy storage systems (BESS), power generation and distribution has become increasingly complex and less predictable. The grid must become more flexible and consumer-friendly to facilitate this bi-directional flow of power and still meet or exceed system reliability requirements. The required rate of change will be exponentially higher than the slow gradual change that occurs today. But, how does one simultaneously increase the rate of change and improve robustness and reliability as the power grid evolves? In this context, medium voltage (MV) substations that step down high voltage (HV) from transmission systems to deliver a supply of electricity to consumers will be vital as will protection and control (P&C) technology [1-5].

01 The SSC600 , shown here, builds on ABB’s solid and proven technological foundation manifested in the renowned Relion® protection and control family.
01 The SSC600 , shown here, builds on ABB’s solid and proven technological foundation manifested in the renowned Relion® protection and control family.
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To date, microprocessor-based control relays have dominated the protection systems in substations, and yet a new possibility has emerged – CPC, a digital software-oriented solution [1,2]. By concentrating P&C into a single device, a CPC device, communication networks permit information flow between different components, bays, substations, and related operators in the substation environment. Having successfully released the ABB Ability™ Smart Substation Control and Protection for electrical systems SSC600, a CPC product, in 2018 →01, ABB has taken further steps by releasing SSC600 SW in 2023; a “virtualized” CPC solution in which software is decoupled from the hardware. Here, the “virtualized” environment is abstracted from the underlying platform, isolated from applications that run on the platform [4,5]. Such innovations could help substations achieve P&C with the flexibility needed at a reasonable cost, thereby supporting the grid to meet the supply and resiliency demands.

Resilience and increased demand for flexibility
Traditionally, resilience is related to maintaining the power balance and protecting against network faults – the ability to bounce back from an event. This contrasts with security of supply, which is the ability to deliver electricity in the quality and quantity that consumers require. Resilience of the grid, however, is evolving to a broader definition [2,3]; Here, resilience is viewed as a complex process occurring over multiple scales, fluctuating – there is a continuum between function and failure – adaptation to change is critical.

Resilience will also determine and limit the maximum speed of systemic change. New innovative technologies namely, 5G, virtualized real-time computing etc. can be connected to the grid but only if by so doing the resilience of this critical infrastructure is not reduced [3]. And, as the role of cyber security increases in importance, the ability to adapt and update the system is needed. Additionally, platforms are required that continue operation even while being updated [3]. First-ever technologies are now available to realize such platforms, eg, machine learning (ML) and artificial intelligence (AI), 5G, and virtualized real-time computing. A complete CPC system, one that incorporates, or accommodates such revolutionary changes is required, and yet the optimal integration of these technologies must be carefully designed.

Protection system evolution – from CPC to virtualized CPC
Over the years, protection in power systems has evolved from electromechanical mechanisms to the microprocessor-controled intelligent electronic device (IED). Relaying is essential to develop a more flexible, interconnected, and smart power system. The IEC 61850 standard released in 2004 not only drives this change, but has instigated the interest in CPC systems. Together with new system engineering tools for support, ABB successfully released the Smart Substation Protection and Control device, SSC600, in 2018 [1-3]. By moving the P&C functionality from multiple bay-level devices to a single central processing unit within a substation, only the process interface functionality remains in the bay-level merging units (MU). One SSC600 device can handle the tasks of 30 protection relays. The targeted benefits are improved functionality and reduced overall lifecycle costs (up to 15 percent) – a boon for the utilities and electricity consumers alike →01.

Recently, an evolutionary step in the CPC concept has emerged: Virtualized Protection and Control (VPC). Applied to P&C, virtualization is the use of software for creation of an abstract image of a traditional P&C solution inside a physical host (a ruggedized computing hardware). Hence, the protection application is no longer tied to a particular centralized device; it is a software image that can be independently deployed to versatile industrial server architectures in different environments. ABB released the world’s first VPC, a virtualized version of SSC600, the SSC600 SW, in 2023. The goal has been to achieve the same reliability as a CPC system but with greater efficiency and to further reduce life-cycle costs.

Enablers for CPC and VPC – IEC standards
Even though the basic functions of substations have remained unchanged for years, data processing and communication solutions are in flux, resulting in the availability of key technical enablers for CPC systems.

The IEC 61850 standard has made fast and standardized Ethernet-based communication more available; the station bus, as defined in IEC 61850-8-1, allows for the elimination of copper wires between numerical protection relay units on the horizontal level, ie, relay-to-relay communications. The process bus, defined in IEC ­61850-9-2, permits digitized information to be shared from instrument transformers or sensors to other relays and, or CPC units, thereby enabling a shift of P&C functions between different relays and, or CPC units at the substation level.

Another vital enabler, defined by IEC 61869-13, is the MU, the interface of the instrument transformers with a relay and CPC unit [2]. The interface accepts current transformer (CT)/voltage transformer (VT), low-energy sensors and binary inputs (BI) and produces multiple time synchronized digital outputs, providing data communication via the logical interfaces. IEC 61850-9-2LE defines a sampling frequency of 4 kHz for 50 Hz networks and IEC 61869-9 defines 4.8 kHz for 60 Hz networks (among other frequencies) for raw measurement values to be sent to subscribers. The MU can also host input/output (I/O) to handle feeder-based digital signals, communicate the digital status of primary equipment, eg, circuit breakers, isolators, earthing switches, to network devices; and receive trip and open or close signals from an external unit through IEC 61850-8-1 station bus.

02 An overview of a CPC system, with redundant CPC devices.
02 An overview of a CPC system, with redundant CPC devices.
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Moreover, Ethernet-based technology and IEC 61850 standard, allow time synchronization to be reached with an accuracy of 1 μs. A GPS or equivalent resource is required in every substation in accordance with IEEE 1588v2 and IEC 61850-9-3.

The communication network must also be highly available and reliable in any architecture utilizing a CPC/VPC system. To address this time-critical need, IEC 61850 standard mandates the use of the IEC 62439-3 standard in which Parallel Redundancy Protocol (PRP) and High-Availability Seamless Redundancy (HSR) are defined. Both methods of network recovery provide “zero recovery time” with no packet loss in case of single network failure – vital for CPC in substations.

Virtualization technology
With IEC standards defined, CPC system evolution forges ahead. Widely used in information technology (IT), in non-real-time applications, virtualization of substation CPC (VPC) is a logical development. Because Hardware Virtualization (HWV), Kernel-based virtualization and OS-level virtualization, are all able to achieve the required deterministic operation and reliability for P&C purposes, the preferred choice depends on performance and overhead demands. Recent studies show that the necessary real-time performance can be achieved with virtualization technologies, containing both virtual machine (VM) and containers [5]: HWV provides the strongest isolation between different VMs, while OS-level virtualized containers provide the lowest overheads.

03 Centralized protection example with numerical protection relays.
03 Centralized protection example with numerical protection relays.
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But why virtualize P&C in a substation in the first place? Because virtualization enables software to be deployed, executed, exchanged, and migrated in isolation from the platform, applications can be flexibly and rapidly deployed in a substation. It would, thus, be easy to maintain and update hardware; customers could deploy applications from different vendors and update functions on demand. But, this is only possible if virtualization can be accomplished in real-time. And this is just what ABB tested and verified.

Architectural options
Before testing the efficacy of CPC and VPC concepts in laboratory and field experiments, ABB evaluated various architectures →04. The right choice depends on the substation’s specific needs, eg, protection philosophy, defined specifications, time critical applications for P&C, redundancy requirements at the physical, functional or communication level, flexibility to adapt to the changes that the power distribution grid is facing today, etc. [3,5,7].

  • 04a Decentralized.
  • 04b Centralized.
  • 04c Hybrid.

04 Substation architecture alternatives.

Traditionally P&C architectures distribute protection in multiple different Numerical Protection Relays (NPR), ‘Decentralized’ →04a but in CPC all the safety critical intelligence is in one device. Here, redundancy ensures that full functional protection is available in case of failure [1] →­02-03,04b. One way to achieve this is to duplicate the central device. Another way to achieve redundancy is to use a hybrid system→04c, a combination of both approaches – a bay-level backup protection (for simplified protection) with the CPC device (for advanced protection) [3,4]. In regard to centralized protection, the hybrid scheme is ideal for retrofitting to existing installations because it allows for the introduction of new functionalities, eg, remote asset management and configurations, upgrades, analytics and advanced applications such as virt-
ualization [6]. Having successfully demonstrated the three architectures, ABB chose the hybrid system approach for the first real-life pilot experiences due to ease of implementation [4,5].

Pilot experiences
ABB conducted the first pilot for the CPC with a hybrid architecture during 2017-2019 together with Finnish DSO Caruna in a 110 kV/20 kV substation with double busbar and single power transformer→05. The substation, located in Noormarkku, Finland, was equipped with a hybrid architecture between June 26, 2017 and Jan. 2, 2019 [1]. During the pilot study, 99 short circuits and 69 earth faults occurred and were all cleared successfully by the CPC device (ABB’s SSC600). The results showed that the CPC technology is satisfactorily reliable and efficient.

05 An overview of the virtualization piloted SW environment.
05 An overview of the virtualization piloted SW environment.
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In addition to the active CPC protection system previously described, ABB built a prototype solution that virtualized ABB’s HW-based CPC solution by wrapping it into a Docker container. Containerization is a lightweight virtualization technology in which containers share the operating system kernel. Such a solution meets the latency demands for substation automation applications with improved real-time capabilities.

ABB’s VPC solution contained two separate VPC containers, running in one host HW that were deployed to the substation in a standby mode – executing identical protection functions as CPC but without the possibility of sending trip commands to the relays [5]. The two VPC containers ran as a pilot in the substation for over a year, from Sep. 27, 2021 to Jan. 5, 2023. The results reported →06 demonstrate that during the examined period both VPCs were able to match the behavior of the physical CPC flawlessly. The protection function events in both VPC images carried the same timestamps in the event log, measured to the ms, as the CPC. The handling of the many faults did not deteriorate the required real-time performance in any way →06 – a marked success.

06 Event Log Comparison for one day, NOO2 as CPC device, NOO_VIRT and NOO_VIRT2 as VPC container images.
06 Event Log Comparison for one day, NOO2 as CPC device, NOO_VIRT and NOO_VIRT2 as VPC container images.
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System benefits and deployment
The results from the CPC systems in operation are on par with results gleaned from the pilot experiments described above [7]. For example, the SSC600 employed by the Finnish utility Parikkalan Valo in 2020, successfully manages their electrical network and assets to ensure the flexibility needed for the future.

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The added flexibility of a fully digital substation solution with CPC or VPC systems yields advantages. When all functionality resides in one SW solution, complete testing can be conducted prior to deployment in a digital simulation environment. With comprehensive simulation tools, it is possible to conduct all required tests without any copper wiring, without any MUs or protection and control relays, thereby facilitating laboratory testing during the early engineering phases. Such tests can help to improve design and simplify later testing phases, thereby potentially improving system reliability [5,7]. Such benefits will ultimately help utility customers achieve the system flexibility they need with lower overhead costs as they seek to improve resilience and security of supply →07 as ever more DERs connect to the power grid. 

Further information
J. Valtari, “The carbon neutral society of the future needs resilient electric grids”, ABB web story, 2021.
ABB global web story, “Virtualization is an important step in bringing clean energy to the world”.
ABB press release, “ABB launches world’s first virtualized protection and control solution”.
ABB website, “Centralized protection for distribution substations”.
ABB web story, “Finnish utility selects ABB’s centralized control and protection solution to take their substation to the next level”.

References
[1] J. Valtari, et al., “Performance analysis of centralized protection and control solution for a distribution substation”, Proceedings. PAC World Conference, 2019, pp. 1 – 9.
[2] A. Sivesind, et al., “Pilot implementation of Centralized Protection and Control – SRP Experience”, ABB White Paper, 2022, pp. 1 – 24.
[3] ABB White paper, “Centralized protection and control – Enhancing reliability, availability, flexibility and improving operating cost-efficiency of distribution substations”, 2022, pp. 1 – 23.
[4] S. Schönborn, et al., “Real-Time Performance of Virtualized Protection and Control Software”, in CIRED, 27th Conference on Electricity Distribution, June 12-15, 2023, pp. 1,817 – 1,821.
[5] J. Valtari, et al., “Real-life Pilot of Virtual Protection and Control – Experiences and Performance Analysis”, in CIRED, 27th Conference on Electricity Distribution, June 12-15, 2023, pp. 2,268 – 2,272.
[6] S. Schönborn, et al., “The virtues of virtualization,” ABB Review 02/2023, pp. 118 – 123.
[7] J. Valtari, et al., “Functional testing of virtualized and centralized protection systems” in CIRED, 27th Conference on Electricity Distribution, June 12-15, 2023, pp. 3,513 – 3,517.
Photo fig. 07: © Martin Mecnarowski/stock.adobe.com

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