Sergio Armando Gutiérrez, Juan Felipe Botero, Natalia Gaviria Gómez, Luis Alejandro Fletscher, Alexánder Leal
The electrical grid is undergoing a fundamental change with the introduction of smart grid technologies. In particular, power substations have been evolving toward more automated systems. Power substation communication networks evolved from infrastructures mostly formed by serial devices to Ethernet-based digital communications networks, accelerating with the introduction of the IEC 61850 set of standards. However, this evolution inherited the shortcomings of the traditional decentralized network management. This article explores the upcoming evolution of IEC 61850 to meet the groundbreaking programmable network technologies: software-defined networks (SDNs) and programmable data planes (PDPs). Here, we describe how recent proposals leverage SDNs to improve network management tasks such as topology discovery, multicast traffic management, and quality-of-service (QoS) provisioning, among others in IEC 61850-based systems. We also outline potential improvements to critical network management tasks in power substations using PDP features such as in-band network telemetry. Finally, we discuss different challenges in the management of the communication networks of smart power substations and addressing them with the implementation of programmable networks.
Power substations (substations for short) are critical infrastructure elements in the provision of electricity service. Their main responsibility is the conversion of high voltages, present in the generation and transmission process, to lower voltages connecting to end users. Substations integrate voltage levels using transformers that perform voltage step-up or reduction and switches used for system reconfiguration, including circuit breakers (CBs) for performing protection operations. Energy markets are evolving to meet specific customer requirements, for example, through pay-per-use services where end users can pay for the exact amount of electricity used. New markets facilitate the participation of different players, including those contributing as energy generators by supplying excess energy from their own generation (such as small wind generators or solar panels) to the grid, supported by utilities introducing customer and supplier satisfaction as an objective. This satisfaction relies on information exchange among the entities involved in the process of energy supply, which depends on a set of mechanisms that enable users to decide how to plan their energy demand. Hence, the development of architectures to better facilitate that exchanged information is very relevant. The increasing size and complexity of the communication infrastructures within power system substations makes management and operation based on human intervention unfeasible. The criticality of these infrastructures, and the challenges associated with resilience, robustness, availability, and security, imply that the management of infrastructures needs to evolve toward automated models based on the exploitation of data available from entities connecting to the infrastructure.
To achieve the purpose of having such architectures while considering design principles such as vendor independence and openness, Technical Committee 57 of the International Electrotechnical Commission developed the IEC 61850 family of standards for the specification of communication protocols and data models for use in substations. An important purpose behind the introduction of this standard was to enable evolution from legacy infrastructures, mostly formed by serial devices interconnected through complex wire meshes, toward digital communication networks, based on well-known technologies such as Ethernet, to enable flexible service models tailored to the satisfaction of different customer needs.
Despite the benefits of using Ethernet-based communication, the technology introduces operational issues and security concerns. If not implemented well, the use of digital communication networks limits scalability of the infrastructure and requires manual configuration of each networking device, thus increasing the complexity of the communication network management. IEC 61850 relies on configurations such as IEEE 802.1Q virtual local area networks (VLANs), and it does not incorporate security mechanisms by design. Hence, the communication infrastructure of IEC 61850 presents limitations to its scalability by relying on VLANs as the mechanism for traffic segregation and is prone to security threats such as replay attacks, false data injections, spoofing, and denial of service, among others.
Two recent paradigms seeing application in enterprise computing applications have the potential to reshape substation computer networks. On the one hand, SDNs have introduced decoupling of the control plane, where algorithms and logical functionalities of the network reside, from the data plane where the actual packet forwarding occurs. On the other hand, PDPs have enabled customization of the parsing and processing of network packets within switches and routers through the deployment of chips that end users can program (rather than configure). Similar to the approach followed in different computer network contexts, researchers are exploring SDNs and PDPs as mechanisms to cope with the security and operational issues that might arise in IEC 61850 infrastructures. For example, some proposals aim at exploiting the functionalities of SDNs to support the network segmentation required to create different broadcast domains to separate the multicast groups associated with different control functions.
In recent times, SDNs have seen implementation in smart substation communication networks. This incorporation might bring several advantages for network management in IEC 61850 infrastructures. For instance, leveraging SDNs provides isolation and slicing to separate the different traffic types in the communication traffic to provide improved QoS. SDNs can also prioritize the traffic associated with critical events in the substation and might simplify network management due to the separation of control and data planes. Moreover, SDNs can provide mechanisms to ensure the resilience of substations by seamlessly rerouting or duplicating traffic upon the failure of the control devices.
This incorporation of SDNs in power systems is in active development by industry, with success cases that confirm its potential. In their 2020 paper, engineers from Schweitzer Engineering Laboratories (SEL) discuss the engineering process for incorporating SDNs in a complex, thermal-based power generation infrastructure in India. The authors describe an infrastructure integrating more than 60 intelligent electronic devices (IEDs) with two supervisory control and data acquisition servers and their respective human–machine interface (HMI) systems. These authors introduce the concept of operational technology SDNs using a proactive configuration of flow rules to define the network’s behavior. According to their analysis, SDNs outperform traditional network approaches by reducing failover times regardless of the network topology.
In addition, with SDNs, it is possible to implement network packet filtering to provide improved security, traffic forwarding based on a match-action model, a security model based on a deny-by-default approach, and proactive behavior for dealing with failover events. In addition to this, SEL also reports two other important study cases based on SDNs. In one case, the U.S. Department of Energy’s National Renewable Energy Laboratory chose a solution based on SEL technology for the Energy Systems Integration Facility, located in Colorado, which includes a research platform for distributed energy and microgrid devices and systems. The solution implemented by this vendor incorporates SDNs for its microgrid controller platform to improve security and manageability of the infrastructure. In another case, they deployed a solution based on SDNs for the operation of Itaipú Dam, operated between Brazil and Paraguay. According to the white paper describing this solution, SDNs provide optimized traffic management, enhanced response to operational events, fast failure recovery (which is critical for such infrastructure), improved cybersecurity, and more precise testing and documentation of operation tasks.
Finally, researchers at the Research Group on Applied Telecommunications at the University of Antioquia in Colombia present a reference architecture for the management of communication networks of substations. This architecture enables an improved approach to security, QoS, and fault tolerance by leveraging the previously mentioned properties associated with SDNs. A certification laboratory validated and assessed this architecture. The certification laboratory allows utility companies to verify the compliance of their network deployments with the IEC 61850 standard, showing important results regarding operational conditions of the infrastructure.
The concept of PDPs has emerged as a complete realization of the original ideas introduced with SDNs. PDPs enable the network owners to specify details of the protocols managed within switches and the actual treatment applied to packets. These programmable forwarding devices can apply custom processing to provide specific functionalities that match the needs of traffic in smart substations. Despite the advantages and the possibility of developing custom packet processing mechanisms, to the best of our knowledge, PDPs have not yet been widely applied in the communication networks of smart substations.
In this article, we present a discussion of the potential benefits that the integration of programmable networks introduces to the communication networks of smart substations based on IEC 61850. The rest of this article presents the following topics. The “IEC 61850 Digital Power Substations” section presents the background on the architecture and protocols integrating digital power substations. The “Network Programmability in IEC 61850” section discusses the possibilities of applying network programmability in the communication networks of smart substations. In the “Challenges and Future Perspectives” section, we state some challenges that need to be addressed when considering network programmability in smart substations and the future areas for research that we foresee to complete this integration.
A power substation is an important component in the chain of generation and supply of electric power as it is in charge of the transformation and distribution of electric energy. A digital power substation is a power substation that fully incorporates the advantages of data networks to improve operation and maintenance in the areas of protection, control, communications, and monitoring. The operation of a digital power substation involves multiple Internet Protocol (IP)-compliant devices that are interconnected through a multilevel network infrastructure based on Ethernet technology with the purpose of forming a communication platform supporting management, monitoring, synchronization, protection, control, and sensing operations (see Figure 1).
A digital power substation is a modern form of a substation automation system (SAS), where the concept of an automation system implies integration of the automated responses of the control, protection, and monitoring processes within this infrastructure as a holistic system. In modern context, the IEC 61850 framework can govern the substation automation process, covering almost all aspects of an SAS to guarantee interoperability of devices from different manufacturers. The standard also defines how management, control, protection, and measurement devices intercommunicate inside a substation. As shown in Figure 2, the model proposed within IEC 61850 is hierarchical with three levels: station, bay, and process. These levels are interconnected via the process and station buses.
The process level is composed of yard equipment [voltage transformers (VTs), current transformers (CTs), and CBs], measurement processing devices [merging units (MUs)], actuators (IEDs) for controlling CBs, and time synchronization (TS) devices (main clock). MUs are devices in charge of acquiring measurements of currents and voltages from the instrument transformers (VTs/CTs), converting these analog signals to digital, performing signal processing and subsequently transmitting them over an Ethernet network according to guidelines outlined in the IEC 61850 standard.
The bay level, located near the yard devices, includes relays, referred to here as IEDs, for protection and control at the physical level. These IEDs continuously process information generated from the MUs to provide continuous and detailed knowledge of the different events occurring in the substation or surrounding power system. The IEDs identify events and take appropriate actions (for example, triggering an actuator to automatically trip CBs for a power line due to the presence of a fault, generating alerts upon indications of problems with the health of equipment such as switches or transformers, or isolating faulty sections of the power network).
The station level provides an overview of the entire SAS, including an HMI workstation that presents the processed data for a local operator to monitor and interact with the different substation processes. At this level, there are also devices that provide connectivity between the power substation and the control center.
There are two physical subnetworks, formed by Ethernet switches, which interconnect the three levels. The station bus provides connectivity between the station-level and bay-level devices, typically implemented in a ring topology. The process bus interconnects the process-level equipment with the bay-level equipment by leveraging resiliency techniques such as the Parallel Redundancy Protocol (PRP), which is a simple protocol used for redundancy in industrial networks, based on the notion of physical redundancy. PRP implements redundancy in a network in the form of redundant switches linked with two independent physical paths. The switches send packets across the two paths simultaneously, and the receiving device accepts the first packet to arrive and discards the second one. If one of the paths fails, packets travel over the other path to guarantee fail-tolerant operation of the network.
The IEC 61850 standard also defines four types of communication services: an abstract communication service interface, a generic object-oriented substation event (GOOSE), SVs (sampled values), and TS to ensure the correct operation of a fully digital substation (see Table 1). Substation owners may also choose to implement a subset of these services, for example, utilizing only GOOSE as an intermediate step toward a fully digital substation.
Table 1. Communication Services Defined in the IEC 61850 Standard.
According to the IEC 61850-5 and IEC 61850-8 recommendations, the communication services are mapped into different communication stacks according to their performance requirements (see Figure 3). For example, the Manufacturing Message Specification (MMS) is transported over IP, whereas GOOSE and an SV are transported directly over Ethernet frames transmitted via multicast.
As mentioned earlier, IEC 61850 mainly concentrates on the digitization of substation communication networks by means of a transition to Ethernet-based systems. Therefore, the adoption of IEC 61850 has propelled the modernization of substation communication systems. Adopting such systems, however, inherits their historical management complexity.
The variety of communications protocols (e.g., SV, GOOSE, MMS, Precision Time Protocol, and DNP3, among others) further complicates network management. For instance, SV and GOOSE rely heavily on data link multicast (transmission to a given set of devices rather than to every device connected to the medium), forcing network devices to be configured with a variety of layer 2 and 3 networking techniques (VLANs, Grid-Based Reliable Multihop Routing Protocol, and Multiple MAC Registration Protocol). The manual configuration of these devices is error-prone and obstructs the dynamic automation of substation communication networks. In addition, security and congestion issues further complicate network management.
On the other hand, network programmability has emerged to provide flexible and customized network management. This recent paradigm for network programmability uses two architectural proposals: SDNs and PDPs. SDNs separate control and data planes and provide a logically centralized control of the network through a programmable control plane. More recently, the emergence of PDPs represents an outstanding advance in the complete realization of the SDN paradigm. PDPs enable complete control of network behavior, from the applications to the packet processing within the forwarding devices, including the definition and parsing/deparsing of custom headers. Consequently, PDPs allow revisiting existing functions for network management. Figure 4 illustrates a comparison of the evolution of the architectures from legacy switches (incorporating control and data planes in the same device) toward a programmable environment using an SDN-based architecture using OpenFlow and P4-based switches.
Figure 4 depicts several aspects illustrating the contrast between traditional networks and programmable networks. On the left side, we present the conceptual structure of traditional network devices. Traditional network devices have tightly coupled and embedded control and data planes. The control plane contains the programs that execute the algorithms involved in tasks such as routing, QoS, and security. These algorithms operate in a distributed way, exchanging information with the corresponding instances running on other devices in the network. The data plane, on the other hand, is only in charge of performing packet forwarding, which might include packet header updating and calculation of checksums. On the right side, we depict elements of a network paradigm based on the combination of SDNs and PDPs. First, SDNs enable the decoupling of control and data planes, which is not possible in conventional forwarding devices. SDNs separate these planes and migrate the control plane out toward a logically centralized entity called a controller or network operating system. Examples of controller implementations are NOX, POX, and Ryu (implemented in Python) as well as ONOS and OpenDayLight (implemented in Java). Network functionalities such as routing become software applications developed using general-purpose languages matching the implementation language of the controller. The applications implementing those network functionalities run in the controller and communicate with the data plane through a set of communication interfaces. Then the forwarding devices perform the actual packet forwarding. The most developed of the interfaces between the control and data planes is the OpenFlow Protocol, specified by the Open Networking Foundation, which has become the de facto standard in SDNs.
PDPs complement the concepts proposed by SDNs, providing a complete realization of the SDN paradigm. PDPs propose programming the packet parsing and processing within forwarding devices according to custom needs specified by network users through specialized programming languages. For instance, the P4 programming language, introduced by researchers at Princeton University in 2014, has become the de facto standard for data plane programmability. In data plane programmability, equipment vendors provide compilers that translate the user-written P4 programs into machine code for the specific target chip in the switch (represented in Figure 4 by the executable and p4 info files, which are output by the compiler). This translation also provides an interface called P4Runtime, which the control plane can use to control the actual packet-forwarding task provided by the switch. Until recently, the focus of SDNs and PDPs was on enterprise network environments such as Internet service providers, wide area networks, wireless 5G and beyond, and, especially, data center networks. Leveraging SDNs and PDPs can achieve this automation of the different aspects of the network management in the context of digital power substations based on IEC 61850.
To cope with the aforementioned management issues, recent installations have included SDNs as a central element of the IEC 61850 network architecture. In fact, manufacturers of power systems equipment, such as SEL, have deployed (proprietary) SDN-based solutions for power substations’ communication networks.
Figure 5 shows an SDN-enabled architecture where a network controller acts as a programmable control plane that enables automated communication among the IEC 61850 architectural levels. Several proof-of-concept approaches have proposed different contributions for automating IEC 61850 communication network management with SDNs. The following are important network management functions automated by SDNs:
PDPs are a natural step beyond OpenFlow in SDNs. PDPs provide network reconfiguration capabilities (the controller can redefine packet parsing and processing in the field), protocol independence, and target independence. These capabilities enable novel features such as in-band network telemetry, an approach where the network packets can contain statistics updated upon the processing of these packets within the network devices, allowing customized network management. In substation communication networks, the introduction of PDPs would help with many network management challenges, such as cybersecurity, congestion control, improving QoS, network infrastructure awareness, and management automation, among others. The next section describes in detail these important challenges and discusses potential alternatives to face these challenges using programmable networks.
The incorporation of PDPs in the communication infrastructure of smart substations introduces several challenges, especially in the context of network management. Next, we discuss some of these challenges and then outline the possible approaches to address them via programmable networks.
The incorporation of SDNs and PDPs in the network of smart substations introduces several possible ways to implement security measurements for these infrastructures. On the one hand, the logical centralization and global visibility of the network provided by SDNs allows effective deployment of applications and algorithms that make security decisions, such as traffic blocking, network segregation, or rerouting. On the other hand, programmable switches have detailed visibility of traffic and enable the ability to perform quick actions on the traffic due to their location. However, despite this advantage, the need for coherence and prompt response without inducing excessive overhead in the traffic processing is a challenge for implementing these security actions. A potential approach to enable intrusion detection inside data plane programmable switches makes use of lightweight machine learning techniques (i.e., binarized neural networks) and shows great improvements in reducing latency and communication overhead over edge network domains.
One of the main applications of PDPs, as reported in the literature, is in-band network telemetry. This application takes measurements of the packets within switches and passes the information derived from these measurements up to the control plane. Thus, the control plane can make decisions by analyzing this information in light of a global view of the network topology. By incorporating these measurements in this analysis at the control plane, aspects such as network congestion can be managed. For example, congestion can by decreased by creating alternate paths that guarantee that critical messages (e.g., type 1 A GOOSE messages) do not become affected by increments of delay due to congestion events.
Communication among devices in smart substations uses protocols such as GOOSE and SV. These protocols in general, and GOOSE in particular, define different types of messages according to the information related to the events that might occur in the infrastructure. For example, there are classes of GOOSE messages associated with critical operations in the infrastructure that have very strict requirements regarding delay. Hence, it is desirable to have the capability to prioritize and provide a differential treatment that can privilege to these critical messages over information or monitoring traffic. The combination of SDNs and PDPs can contribute to addressing this challenge by seamlessly configuring dedicated paths through devices capable of distinguishing and performing expedited forwarding of critical packets.
An important aspect of the communication infrastructure in smart substations is communication resilience in terms of providing alternate communications paths upon the failure of critical nodes. Introducing redundant paths by duplicating infrastructure improves resilience but also increases CAPEX and operational expenses and increases network complexity. By leveraging SDNs and PDPs, it is possible to avoid the need to duplicate infrastructure. Network-resilience improvement then results from taking advantage of the global visibility of the network topology, which is inherent to SDNs. This global visibility, in combination with functionalities such as in-band network telemetry, might be useful to detect the degradation of devices connected to the network in advance of failure, while also providing, in advance, alternate paths for communication among critical devices. This guarantees continuity of the network operation by carefully observing the network topology behavior with SDNs and observing the particular dynamics of the network traffic by leveraging PDPs.
In the pursuit of true resilient and trustable infrastructures, which are vital in the context of critical infrastructures, automation of network management operations is a vital need. For instance, the collection of statistics to support decision making, possible forecasting of failures, or service degradation is a fundamental task. As discussed previously, programmable devices can implement in-band network telemetry. Thus, network management systems can access information that is more accurate rather than gathering statistics through periodic polling. In addition, the provision of “first-hand” measurements from network devices can be leveraged to design resilient and proactive security mechanisms based on data analytics implemented at the control plane. By using these data analytics, it is possible to anticipate breakdowns and react to them in advance by enabling alternate communication paths to overcome critical situations such as attacks or communication failures.
Substation management automation is paramount in the migration toward a next-generation network core (i.e., network infrastructure leveraging SDNs, PDPs, and management based on data analytics to support automation for the communication of core operations in the substation). In this environment, the new architecture needs to support the dynamic implementation of a variety of different functionalities, such as cybersecurity. The application of automatic software vulnerability management and security patch updates for substation products are essential security measures in the communication environment. In the same way, critical tasks such as updating the firmware of different families of switches and the reception and execution of actions in response to alerts from the manufacturers must occur without human intervention.
The market needs an open ecosystem for substation controllers and engineering tools, especially when proprietary solutions are the common scenario today. Another issue of great interest is automating policy management for threat intelligence to increase the transparency of monitoring tasks. Additionally, information sharing between network functionalities such as intrusion detection systems or security information and event management needs continuous updating with threat intelligence information.
Within the hierarchy of IEC 61850 messages, there are different priorities according to their use cases. In particular, the trip messages (type 1 A GOOSE), associated with command or status notifications and the raw messages (SV, type 4) require transmission times between 3 and 10 ms. These strict time requirements imply that any processing performed on the packets associated with these messages must not induce overhead that could compromise these time requirements. Despite the advantages PDPs introduce in terms of flexibility and expressiveness through custom packet processing, there exists a critical tradeoff between these advantages and the stringent time requirements defined by parts of IEC 61850.
In general terms, there is no concept of a “standard substation.” Actual deployments might differ in the topology, configuration, number of instances of devices (IEDs, MUs, and actuators), and vendors of these devices. Despite the fact that IEC 61850 is an initiative for standardization and interoperability, some aspects such as the actual capabilities available in devices might vary. Hence, some particular aspects of the network communication, such as the fields contained in GOOSE/SV frames and their interpretation might be different across different deployments. This fact constitutes a challenge because then, each deployment and the implementation solution based on network programmability needs to be customized according to the particular elements applied for such a solution.
One of the areas that might become important to take advantage of in network programmability in smart substations is security. The research literature presents a wide set of proposals to develop intrusion detection and prevention systems for substation infrastructures. Leveraging features provided by SDNs and PDPs can improve applying these security solutions. However, an important challenge in developing potential machine learning solutions is having datasets to train the models for these solutions. According to the literature, most of the approaches use either private datasets or general-purpose datasets not tailored to the protocols of smart substations. There are only a couple of public datasets, such as EPIC and RICsel21. However, not all information in these datasets is available, especially the information associated with the particular capabilities of the devices used to obtain the data. As a result, the development of general solutions for security of smart substations based on machine learning and leveraging programmable networks might need to rely on transfer learning (an artificial intelligence technique that uses a model previously trained in a different domain and applies it to a different one) to achieve a certain level of generality.
In addition to taking advantage of the potential for integrating SDNs and PDPs in the core of substations, it is essential to develop a framework that simultaneously accomplishes the security requirements of IEC 61850 and those coming from the Internet world (i.e., a framework capable of addressing the tradeoff between meeting the strict requirements of IEC 61850, especially in terms of processing times for packets, along with the computation time required by machine learning techniques by leveraging programmable networks). Risk management in smart substations might leverage the properties of traffic visibility and logical centralization provided by SDNs and PDPs to improve security and resilience, but it must assure that enabling this property does not hamper the correct processing of critical GOOSE or SV messages.
In this article, we outlined some elements in the evolution of the communication infrastructure of smart substations. We discussed some of the basic elements of IEC 61850, concentrating on its network architecture and operational requirements, and the resulting communication needs in substations. We also presented some operational challenges that have been brought by digitization of the communication infrastructure of smart substations. We consider that the combination of SDNs with PDPs provides a big opportunity to introduce novel and effective solutions to address these operational challenges. However, two aspects of applying these tools are still open research problems. The first is the actual details of implementing these solutions. Determining which logic to implement at the control plane versus what to offload toward PDPs is not a trivial problem. A second challenge is the tradeoff between granularity and visibility of traffic processing based on functionalities at the PDP versus the strict delay requirements defined for traffic in power substations. Hence, in the short term, there will be an increasing interest from academia and industry in further investigating these open research problems.
This article was supported by the Ibero-American Science and Technology Program Ibero-American Programme on Science and Technology for Development (CYTED Project 519RT0580) and the General System of Royalties from Colombia (BPIN code 2020000100381).
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Sergio Armando Gutiérrez is with Universidad de Antioquia, Antioquia 050010, Colombia.
Juan Felipe Botero is with Universidad de Antioquia, Antioquia 050010, Colombia.
Natalia Gaviria Gómez is with Universidad de Antioquia, Antioquia 050010, Colombia.
Luis Alejandro Fletscher is with Universidad de Antioquia, Antioquia 050010, Colombia.
Alexánder Leal is with Universidad de Antioquia, Antioquia 050010, Colombia.
Digital Object Identifier 10.1109/MPE.2023.3288579
Date of current version: 21 August 2023
1540-7977/23©2023IEEE