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Summary
In 1965, the northeast section of the US experienced a massive blackout. In response, the Electric Power Research 
Institute (EPRI) helped create and implement new metering and monitoring systems using mini-computers and programmable logic controller (PLC)-based SCADA systems to help guard against similar failures. The first of these systems emerged within ten years after the blackout and many are still in service today. Early systems employed radio and direct-wired connections using Modbus, Remote Terminal Unit (RTU), RP-570, Profibus, or Conitel protocols to collect information in a substation and pass it to the mini-computer or PLC, which was often located somewhere else.
This ARC Advisory Group ARC View will explore how today’s “digital substations” have evolved from early SCADA systems. Digital substations use a combination of networking technologies developed specifically to meet the protection, control, and remote operational needs of a modern substation, plus sophisticated software applications that can better manage grid assets.
The world’s use of energy for transportation, buildings, and industry is moving from fossil-fueled to carbon-free electric power generation. With a rapid expansion of distributed generation technology and new customer loads to be served, the electric grid needs to keep pace. The modern digital substation is a key part of that solution. It can help reduce grid failures and achieve high reliability at low cost, even with today’s increasing fraction of renewable generation.
The Digital Substation
The term “digital substation” is increasingly applied to electrical substations that use process bus technology. Process bus replaces hard-wired connections with Ethernet communications. Operation and control are executed by distributed intelligent electronic devices (IEDs) interconnected by IEC 61850-based communications networks. IEDs can measure and communicate variables like current or voltage or they can be switchgear like relays; but IEDs communicate digitally on an Ethernet network for protection, measurements, metering, or monitoring and can include legacy serial links as part of the IEC 61850 network. A digital substation can use other means of communications, but IEC-61850 has become the modern worldwide communication protocol standard for substations.
More than a protocol, or even a collection of protocols, IEC 61850 is a comprehensive standard designed from the ground up to operate over modern networking technologies. It delivers functionality not available from legacy communications protocols. It can provide a communications service interface that supports services such as generic object-oriented substation events (GOOSE), sampled measured values (SMV), logs, and other services. These unique characteristics of IEC 61850 significantly reduce costs associated with designing, installing, commissioning, and operating power systems.
Managing Grid Assets
What is needed to control an electric grid in a way that improves reliability and keeps power costs low? With limited capital budgets, utilities must make choices related to long-term spending. These include:
- Considering all pertinent factors to determine which projects will provide the greatest risk reduction
- Deciding which aging equipment assets can be upgraded cost-effectively
- Deciding whether additional capital expenditures can be justified to the regulator or other stakeholders
- Determining the most effective way to deploy resources during an outage
The process bus digital communication standard supports interoperation of IEDs from different vendors and makes a modern substation “digital.” When process bus devices are configured properly with the IEC 61850 standard, they can provide fast, reliable, and secure communications to support equipment protection, remote monitoring, and remote control. Process bus can also support situational awareness at control centers based on accurate and timely measurements from all corners of the grid. This data can enable coordination between transmission segments and between transmission and distribution operators by connecting the data to APM applications.
While this equipment is provided by a large number of suppliers, it must all interact in a coordinated manner. In the past, RTUs, PLCs, or I/O devices collected analog signals. Subsystems then digitized these signals using multiplexers and early analog-to-digital (A/D) converters. Communications to remote locations were often performed with proprietary, vendor-specific communications. MODBUS or DNP3 protocols provided a level of standardization. However, these legacy communications have limits when it comes to signal accuracy, sample frequency, redundancy, and communications speed. While many older substations today continue to use these communications, the new IEC 61850-based process bus has emerged as the world standard to interconnect substation IEDs from different suppliers in a uniform, but flexible way to address previous limitations. Communications with process bus can be very fast and synchronized down to nanoseconds. Process bus can run over TCP/IP networks or substation LANs using high-speed switched Ethernet to obtain the necessary response times (below four milliseconds for protective relaying). Using the station LAN to exchange these signals reduces infrastructure costs associated with wiring, trenching, and ducting.
Conclusion
New asset performance management functionality connected directly to the digital substation offers the promise to support all three priorities for the electric grid: high reliability, low cost, and regulatory compliance. But developing a viable APM solution for the electric grid requires both significant domain expertise for these types of assets and a 
thorough understanding of how the assets work together as a system. Mathematical models based on first principles, combined with operating statistics to model asset behavior, are the key methods used to create a digital twin. Digital twin refers to a dynamic digital replica of the actual physical asset and how it interacts with the larger grid and the humans that operate and maintain it. The twin can include spatial geometry of the asset and its location on the grid as well as thermodynamic and electrical behaviors.
When applied effectively, APM helps reduce both OpEx and CapEx based on predictive and prescriptive analytics that generate operational savings and/or defer the need for capital investment. With reduced outages, APM can also help utilities achieve regulatory compliance.
As ARC learned, the Hitachi ABB Power Grids APM solution provides asset health and performance insights to help prevent critical failures while optimizing asset lifecycle costs. The solution uses digital twin technology and integrates online data from existing historians. It can also use state-of-the-art IIoT (Industrial Internet of Things) connectivity from the substation to the cloud, enabling utilities to leverage both their online and offline data to drive more intelligent, condition- and risk-based approaches to asset management. By combining the capabilities of data capture, integration, visualization and analytics, utilities gain new insights through predictive, prescriptive, and prognostic views of their systems. The solution aligns with key industry standards such as ISO 55000 and PAS 55. Learn more from this white paper on The Next Generation Digital Substation.
Hitachi ABB Power Grid APM helps utilities know when failures are likely to occur and what the ramifications of those failures would be. Armed with this information, utilities are better able to meet key objectives, including:
- Cost-effectively managing asset health
- Effectively addressing identified risks
- Prioritizing repair-and-replace decisions
- Performing “what-if” analyses and contingency planning scenarios
Hitachi ABB Power Grids
Formed in 2020, Hitachi ABB Power Grids is a global technology leader with a combined heritage of almost 250 years. Headquartered in Switzerland, the business serves utility, industrial, and infrastructure customers across the value chain. With expertise in emerging areas like renewables integration, energy storage, electrified mobility, and smart cities, Hitachi ABB Power Grids is well-positioned to help organizations around the world navigate the transition to an intelligent and distributed energy future.
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Keywords: Substation, Substation Automation, Digital Substation, Asset Performance Management, APM, Electric Grid, Transformer, ARC Advisory Group.