Twenty Years of Process Bus: Transforming Digital Substations
by Alex Apostolov, Editor-in-Chief
In the past two decades we have witnessed a fundamental transformation in PAC through process bus technology. Since the publication of IEC 61850-9-2 in 2004, the power industry has gone from ambitious promises to practical reality, learning invaluable lessons about implementing digital communication systems in critical infrastructure.
The initial vision was exciting: replace thousands of copper cables with fiber optic networks carrying digitized measurements and control signals. Early adopters in Europe and Asia embraced process bus with enthusiasm, anticipating dramatic reductions in installation costs, elimination of cable yards, and unprecedented operational flexibility. Merging units would digitize signals at the process level, while protection and control devices could relocate to climate-controlled environments away from harsh switchyard conditions.
However, reality proved more challenging than theory. The first major obstacle was interoperability. Despite IEC 61850 being an international standard, different manufacturers interpreted specifications differently, leading to compatibility issues. Utilities quickly learned that having a standard did not automatically guarantee multi-vendor interoperability The emergence of the 9-2 Light Edition profile helped moving forward.
Timing and synchronization emerged as critical challenges. Protection functions, particularly differential schemes, required microsecond-level accuracy. Any timing errors directly translated into measurement inaccuracies that could compromise protection performance. The adoption of IEEE 1588 Precision Time Protocol helped, but introduced new complexities around network switch capabilities, GPS vulnerabilities, and compensation for network asymmetry.
The period from 2014 to 2018 marked significant maturation. Standards evolved with IEC 61869-9 specifically addressing digital instrument transformers. Industry working groups published practical application guides that bridged the gap between theoretical standards and real-world implementation. These resources provided crucial guidance on network design, testing procedures and commissioning workflows.
Equipment reliability improved dramatically as manufacturers refined designs based on field experience. Second and third generation merging units demonstrated enhanced environmental protection and electromagnetic compatibility. Non-conventional instrument transformers using Rogowski coils and optical sensors became more accurate and reliable. Testing tools evolved from basic monitors to sophisticated analyzers capable of characterizing timing accuracy and detecting quality issues.
Network design matured as engineers gained experience with the unique requirements of time-critical Ethernet communications. The industry developed best practices for traffic engineering, redundancy architecture and Quality of Service mechanisms.
Successful implementations required expertise spanning both electrical engineering and data communications, demanding new skill sets from substation personnel. Production deployments after 2016 provided extensive operational data. The business case proved nuanced -installation savings were real but often smaller than projected, while engineering costs increased due to specialized expertise requirements. However, lifecycle benefits emerged in unexpected areas: reduced copper theft, improved diagnostic capabilities and simplified modification procedures. When properly accounting for all factors over typical 25–30-year substation lifecycles, economics generally favored process bus for new construction.
The most successful utilities shared common characteristics: substantial investment in training, development of internal expertise and adaptation of operational procedures. Organizations treating process bus as simple wiring replacement without changing maintenance practices faced more difficulties. Fault investigation required new approaches focused on network traffic analysis and digital diagnostics rather than traditional signal measurements.
Long-term reliability data validated well-engineered systems. Properly designed installations using mature equipment achieved availability meeting or exceeding conventional architectures. Protection performance was excellent when systems were correctly configured, with digital processing offering advantages in limiting CT saturation and detecting high-impedance faults.
Recent years have seen Process Bus integrate with broader digital transformation initiatives. Cybersecurity became paramount, with IEC 62351 providing security extensions for authentication and encryption. High-resolution digital data enables advanced analytics, with machine learning algorithms identifying incipient failures and optimizing protection settings. Digital twins leverage process bus data for sophisticated simulation capabilities.
Hybrid architectures emerged, recognizing that full digital implementation may not be optimal for all applications. Some utilities adopt “process bus ready” approaches, installing digital infrastructure while initially maintaining conventional connections.
Twenty years of process bus experience demonstrates that transformative change in power systems is achievable but requires persistence and holistic approaches. Success demands not just technical excellence but also standardization refinement, comprehensive training, integrated system engineering, rigorous testing and organizational change management. As the power grid evolves toward greater digitalization and complexity, process bus provides essential infrastructure for the observability and controllability needed for future grid operations.
The foundation established over two decades positions the industry well for continuing evolution in substation PAC technology.
“The best way to predict the future is to invent it.”
Alan Kay
