CIGRE Study Committee B5 has opened a new working group — WG B5.90 — tasked with writing the first dedicated guidelines for commissioning and testing of fully digital protection and automation control systems (PACS). The Terms of Reference for WG B5.90 were approved by CIGRE on 6 January 2026. The working group is convened by Yao Hui (China).

The formation of this working group represents an institutional response to a practical gap: as utilities commission substations built entirely on IEC 61850 process bus architecture, the industry lacks a standardised framework for how to test them — from factory acceptance through to operational deployment.

What the Working Group Will Produce

According to the Terms of Reference, WG B5.90 will develop guidelines covering three stages of the commissioning lifecycle for fully digital PACS:

  • Factory Acceptance Testing (FAT) — verifying system behaviour before equipment leaves the manufacturer
  • Site Acceptance Testing (SAT) — validating integrated system performance at the installation site
  • Operational testing — confirming correct function in a live grid environment, including maintenance testing during service

The scope is specifically oriented toward fully digital architectures — substations where IEC 61850 process bus replaces conventional copper secondary wiring end-to-end, including merging units for current and voltage measurement and GOOSE-based trip circuits.

Why Commissioning Fully Digital Substations Is Different

In a conventional substation, commissioning follows a well-established workflow: trace the copper wiring, inject test currents, observe relay responses, verify tripping. The tools and procedures are understood by a generation of protection engineers.

A fully digital substation presents different challenges. Merging units convert analogue measurements from instrument transformers into sampled values (IEC 61850-9-2). Protection IEDs subscribe to these sampled values over Ethernet. Trip signals are sent as GOOSE messages — also over Ethernet — rather than via hardwired contacts.

Testing this architecture requires: - Injecting sampled value streams rather than analogue currents - Verifying GOOSE publication and subscription parameters - Confirming network timing and latency bounds that affect protection coordination - Testing behaviour when network segments fail or degrade

These are not minor variations on existing test methods. They require specific tools, test procedures, and criteria for what constitutes a successful test.

The problem is compounded by the multi-vendor nature of most digital substation projects. Merging units, protection IEDs, switches, and engineering tools typically come from different manufacturers. Interoperability at the system level — not just at the device level — must be verified during commissioning. This is precisely where standardised guidance is most needed.

The Context: Building on Prior CIGRE Work

WG B5.90 does not start from scratch. The Terms of Reference explicitly reference three foundational CIGRE Technical Brochures: TB 401, TB 637, and TB 760 — the body of CIGRE work that established how IEC 61850 based protection systems are specified, configured, and functionally tested. The working group also draws on outcomes from the Paris Session 2024, specifically Preferential Subjects PS1 and PS2.

WG B5.90 extends this accumulated knowledge into a full commissioning framework applicable across the complete project lifecycle — from factory acceptance through site acceptance to operational deployment.

This sequencing reflects the maturity trajectory of fully digital substation technology. Earlier working groups and technical brochures defined how process bus systems are designed, specified, and functionally tested. WG B5.90 now addresses the remaining gap: a standardised methodology for commissioning and accepting the complete system across all project phases.

What This Means for Engineers

For protection and automation engineers working on digital substation projects today, the practical implication is this: currently, commissioning procedures for fully digital PACS vary significantly between projects and between organisations. Some utilities have developed internal methodologies. Others adapt conventional procedures, accepting gaps.

The WG B5.90 guidelines, when published, will provide a common reference framework. This matters for: - Project specifications: owners will be able to reference standardised commissioning criteria in tender documents - FAT and SAT scope alignment: vendors and contractors will work to agreed test coverage expectations - Maintenance planning: operational testing procedures will provide a basis for periodic verification after handover

The working group is expected to draw on experience from the growing number of fully digital substations now in service globally — including process bus deployments in Europe, Africa, and the Middle East commissioned in the past several years.

What Remains to Be Defined

The Terms of Reference for WG B5.90 set the scope but do not predetermine the conclusions. Several technically open questions will need to be addressed during the working group's programme:

  • How to handle testing of cybersecurity controls within the digital architecture
  • How to address SAT when not all system components can be brought together on-site simultaneously
  • What level of simulation is acceptable as a substitute for physical injection testing
  • How to define acceptance criteria for network-dependent functions (timing, redundancy switching)

The publication of specific guidelines is expected over a multi-year working group programme. According to the Terms of Reference, the final Technical Brochure is scheduled for Q3 2029. Member recruitment is underway, with the working group formation phase running through Q1 2026.

Source: CIGRE, Terms of Reference — WG B5.90 "Guidelines for commissioning and testing of fully digital PACS", approved 6 January 2026. TC Chairman: Rannveig S. J. Loken.