UK Power Networks operates distribution networks across South East England with a rapidly growing population of distributed energy resources — solar farms, battery storage, waste-to-energy plants. Every new DER connection means updated protection settings across multiple substations. Every relay model change means firmware qualification, spare parts logistics, retraining. At scale, the traditional model — one dedicated relay per bay, one vendor per relay — becomes a coordination bottleneck.

The Constellation project is UK Power Networks' attempt to break out of this. Funded by Ofgem's Network Innovation Competition (budget: £17.82 million, May 2021 to September 2026), the idea is to replace bay-level protection relays with virtualized protection software running on substation computers. Bay protection, wide area protection, DER management, adaptive settings — all as virtual machines on shared hardware, communicating over IEC 61850 process bus internally and over Vodafone 5G between sites.

In January 2025, the first Constellation substation went live in Maidstone, Kent. The Allington Energy from Waste plant became the first distributed generator connected through the new system. Five more smart substations are planned across South East England before the trial closes in September 2026.

From Centralized to Virtualized

The starting point is centralized protection and control (CPC). ABB's SSC600 consolidates bay-level protection onto a single device — one unit handling up to 30 bays via IEC 61850 process bus, replacing a panel of individual feeder relays.

The SSC600 SW, launched by ABB in 2023, takes the next step: it decouples the protection software from the hardware. It runs on Linux KVM or VMware Edge Compute Stack (ESXi 7.x and later), on standard Intel Xeon Gold processors. Multiple SSC600 SW instances can share a single server, covering substations larger than 30 bays. The protection algorithms are the same proven code — only the execution platform changes.

For Constellation, this opens up a specific possibility: multiple vendors' protection solutions coexisting on the same substation computer. ABB provides centralized bay protection and wide area protection. GE Vernova contributes the PhasorController for local edge intelligence and DER management. Siemens delivers adaptive protection — automatic update of protection settings via IEC 61850 MMS. All run as software on shared infrastructure.

The Architecture

The Constellation architecture has three layers.

At the process level, merging units at each bay digitize instrument transformer measurements and publish them as IEC 61850-9-2 sampled values onto the process bus LAN. Breaker control commands travel back as GOOSE messages per IEC 61850-8-1 over the same network. There are no bay-level IEDs in this architecture — the MUs and breaker I/O connect directly to the centralized protection via Ethernet switches.

At the station level, substation computers host the virtualized protection functions. Each protection application runs in a dedicated virtual machine on VMware ESXi. The system is fully duplicated — two substation computers, redundant Ethernet switches — with Parallel Redundancy Protocol (PRP) for seamless network failover. Precision Time Protocol (PTP) synchronizes all devices.

At the wide area level, substations and DER sites communicate over Vodafone's 5G SA network using R-GOOSE (routable GOOSE). Protection messages travel between geographically separate sites, not just between bays within a single substation.

flowchart BT
    subgraph PL["Process Level"]
        CT["CTs / VTs"] --> MU["Merging Units"]
        CB["Circuit Breakers"]
    end

    subgraph PB["Process Bus LAN (PRP redundancy)"]
        SW["Ethernet Switches"]
    end

    subgraph SL["Station Level"]
        SC1["Substation Computer A\n(VMware ESXi)"]
        SC2["Substation Computer B\n(VMware ESXi)"]
        VM1["VM: Bay Protection\n(ABB SSC600 SW)"] --- SC1
        VM2["VM: Edge Intelligence\n(GE PhasorController)"] --- SC1
        VM3["VM: Adaptive Protection\n(Siemens)"] --- SC1
    end

    subgraph WA["Wide Area Level"]
        WAN["Vodafone 5G Network\n(network slicing)"]
        DER["DER Site\nSubstation Computer"]
    end

    MU -->|"IEC 61850-9-2\nSampled Values"| SW
    SW -->|"IEC 61850-8-1\nGOOSE"| CB
    SW --> SC1
    SW --> SC2
    SC1 -->|"R-GOOSE\nover 5G SA"| WAN
    WAN -->|"R-GOOSE"| DER

Wide Area Loss-of-Mains Protection

Constellation also implements a wide area protection scheme for DER loss-of-mains (LoM) detection — this is where the 5G link earns its place in the architecture.

Traditional LoM protection relies on local measurements — typically rate-of-change of frequency (ROCOF). The problem is well known: during wide-area frequency disturbances (a large generator tripping somewhere on the transmission system, for example), ROCOF relays at DER sites can falsely interpret the frequency deviation as islanding and trip the generators off. This cascading disconnection of DER makes the frequency event worse.

Constellation's approach combines five functions into a coordinated scheme:

Transfer trip disconnects islanded DER units when the upstream breaker opens — a direct command over 5G R-GOOSE, no local frequency measurement needed.

ROCOF-based blocking is the part worth studying. When the centralized protection at the primary substation detects a system-wide frequency disturbance (not a local island), it transmits a "block ROCOF" command via R-GOOSE to all connected DER sites. The DER's local ROCOF protection is inhibited for the duration of the disturbance, preventing false trips.

Safe reclosing prevents unsynchronized reconnection of DER after an islanding event.

Communication supervision continuously monitors R-GOOSE message reception. If the 5G link drops, the local ROCOF backup activates as a fallback.

Local ROCOF backup runs continuously unless blocked by a wide area command — guaranteeing that protection is never lost, only refined.

sequenceDiagram
    participant PS as Primary Substation<br/>(Centralized Protection)
    participant 5G as 5G Network<br/>(R-GOOSE)
    participant DER as DER Site<br/>(Local Protection)

    Note over PS,DER: Normal operation — local ROCOF active at DER

    PS->>PS: Detects system frequency disturbance<br/>(ROCOF > 1 Hz/s, not local island)
    PS->>5G: R-GOOSE: Block ROCOF
    5G->>DER: R-GOOSE: Block ROCOF
    DER->>DER: Local ROCOF inhibited

    Note over PS,DER: Frequency recovers — no false DER trips

    PS->>5G: R-GOOSE: Unblock ROCOF
    5G->>DER: R-GOOSE: Unblock ROCOF
    DER->>DER: Local ROCOF re-enabled

What the Lab Tests Showed

Before any hardware went into the ground at Maidstone, the Constellation team ran extensive laboratory tests. The setup used a real-time power system simulator feeding two centralized protection units via IEC 61850-9-2 sampled values. The simulated network modeled 33 kV busbar sections (Main 1 and Main 2) with multiple DG connection points. A separate simulator injected configurable delays into R-GOOSE messages to replicate 5G latency.

The PAC World case study (Kulmala et al.) reports the results of the ROCOF blocking test in detail. During the test, the system frequency declined below 47 Hz for approximately 300 milliseconds, with the rate-of-change exceeding the 1 Hz/s threshold. The centralized protection detected the disturbance, classified it as system-wide (not a local island), and transmitted block-ROCOF commands to four DG units via R-GOOSE. No false tripping occurred — the frequency recovered above the underfrequency protection threshold before the 500-millisecond operate time elapsed.

The authors' conclusion is direct: "virtualized centralized protection fulfills protection requirements with set delays and reliability equivalent to dedicated hardware, on condition that the hardware fulfills the requirements defined for it."

That last clause matters. Virtualization does not magically make bad hardware acceptable. The substation computer must deliver consistent, low-latency network I/O. CPU and memory resources must be reserved — not shared with non-critical workloads. PTP synchronization must be maintained. These are engineering constraints, not theoretical risks, and the Constellation team had to address each of them during integration testing at the University of Strathclyde's Power Networks Demonstration Centre (PNDC) near Glasgow.

From Lab to Field

The project follows four phases: lab testing, PNDC integration, passive network trials (system monitors alongside existing protection), and active network trials (system controls the network). After that — BAU write-up and rollout planning.

gantt
    title Constellation Project Timeline
    dateFormat YYYY-MM-DD
    axisFormat %Y

    section Project
    Constellation (Ofgem NIC)             :2021-05-04, 2026-09-29

    section Design & Lab
    System design & development            :2021-05-04, 2022-12-31
    Laboratory testing (ABB)               :2022-06-01, 2023-06-30

    section PNDC Integration
    PNDC test environment build            :2023-01-01, 2023-12-31
    Maidstone WAP integration & SAT        :done, 2023-06-01, 2023-12-31

    section Field Trials
    Maidstone passive network trial        :active, 2025-01-21, 2026-03-31
    Ofgem Deliverable 5 submitted          :milestone, 2024-11-29, 0d
    Active network trials (planned)        :2026-04-01, 2026-09-29

    section Milestones
    Vodafone 5G partnership announced      :milestone, 2021-07-22, 0d
    First smart substation live            :milestone, 2025-01-21, 0d
    Trial end                              :milestone, 2026-09-29, 0d

Note: exact phase boundaries are approximate where public sources give only ordering, not specific dates. Milestones with exact dates are sourced from UKPN, Vodafone, and Ofgem filings.

The Maidstone installation is a passive network trial — the smart substation monitors and analyzes alongside existing protection, without being the primary protection system. A deliverable covering "review and insights following site installation and learning from mid trial passive network demonstration" was submitted to Ofgem on 29 November 2024. The project plan also includes an active network trial phase and a BAU write-up before the trial closes in September 2026.

Where the Capacity Comes From

UK Power Networks estimates that rolling this approach across their network could unlock 1.4 GW of additional DER connection capacity — without building new infrastructure. The mechanism is twofold. Wide area ROCOF blocking eliminates false DER disconnections during system frequency events, which means DNOs can connect more DER to the same feeders without exceeding their risk threshold for cascading trips. Adaptive protection updates settings dynamically via MMS based on real-time network topology, replacing static worst-case calculations that leave capacity on the table. The UKPN press release puts the potential headroom at up to 50% additional capacity "when it is safe to do so."

The Full IEC 61850 Stack, Finally Working as Designed

For years, many engineers have treated IEC 61850 as "just another protocol" — often limited to GOOSE for interlocking or MMS for SCADA polling, with sampled values dismissed as too complex and too expensive for distribution. Constellation is a case where the full stack works together and the result is more than incremental. SV (9-2) digitizes the process bus. GOOSE (8-1) carries trip commands. R-GOOSE extends protection signaling across a 5G WAN. MMS delivers real-time settings updates for adaptive protection. Remove any one of these and the architecture falls apart.

Virtualization raises its own set of engineering questions. Which hypervisor? What are the worst-case latencies under load? How are CPU and memory resources partitioned between protection VMs and everything else on the server? The Constellation team evaluated VMware ESXi, Linux KVM, and Docker containers with PREEMPT_RT patching. These are not new questions — back in 2019, commissioning experience with ISAS-based centralized protection already showed that kernel dependencies, NIC driver compatibility, and real-time scheduling are practical blockers that consume months of project time (Anoshin, Golovin, Svistunov, PAC World Issue 050). Constellation operates at a larger scale, but the qualification challenges are the same.

5G is a viable wide area bearer for protection signaling — with conditions. Network slicing provides the low-latency, high-reliability channel that R-GOOSE needs. A best-effort mobile broadband connection would not be acceptable.

The multi-vendor model raises questions on both sides of the table. For vendors, the shift from selling a self-contained relay to delivering a software component on someone else's hardware changes the product, the support model, and the commercial relationship. For utilities, a substation where ABB provides bay protection, GE Vernova runs DER management, and Siemens handles adaptive settings means there is no single vendor responsible for the system as a whole. Who owns the integration? Who do you call at 2 AM when a protection VM fails to start after a server reboot? These are not technical questions — they are procurement and operational questions that the industry has not yet answered.

Sources

  1. Kulmala, A., Raipala, O., Hovila, P., Yazadzhiyan, B., Dantas, R., Scoble, C. "Virtualized Centralized Protection and Control — Constellation Project Case Study." PAC World. pacw.org

  2. UK Power Networks. "Constellation." UKPN Innovation. innovation.ukpowernetworks.co.uk

  3. ABB. "ABB launches the world's first virtualized protection and control solution." News center, 2023. new.abb.com

  4. UK Power Networks. "UK's first smart substation installed as next generation of power technology." 21 January 2025. ukpowernetworks.co.uk

  5. Vodafone UK. "World first: UK Power Networks to use Vodafone 5G in smart substations." 22 July 2021. vodafone.co.uk

  6. GE Vernova. "UK Power Networks: World's First Smart Substation." gevernova.com

  7. ABB. "ABB technology enables UK grid to integrate more renewable energy." News center. new.abb.com

  8. UK Power Networks. "Constellation Project Progress Report." December 2024. cloudfront.net (PDF)

  9. Anoshin, A., Golovin, A., Svistunov, N. "Software Based Centralized Protection: commissioning experience." PAC World, Issue 050, December 2019. pacw.org