MODULE 03 · ELECTRICAL ARCHITECTURE · ALY-DC-ELEC-SLD-001

400 kV to rack busway, behind one meter.

The live single-line diagram of the behind-the-meter campus: a 900 MW grid connection at the SSEN Alyth 400/132 kV substation, the Seagreen private wire, and a 600 MW grid-forming BESS between them and 405 MW of GB300 load. Select an operating mode — breakers, flows and dispatch re-route exactly as the microgrid controller would drive them.
Grid Seagreen private wire BESS IT load
SSEN TRANSMISSION — 400 kV NETWORK NESO-operated · 900 MW BCA (Gate 2, signed) SEAGREEN OFFSHORE WIND — PRIVATE WIRE ≈400–500 MW · Constellation Energy PPA · dedicated cable · ASPIRATIONAL Alyth Solar & Battery 400/132 kV 2 × 500 MVA · SSEN-owned 87T diff · SSEN DTT source FISCAL METER · BEHIND-THE-METER BOUNDARY — everything below shares the consented BESS connection agreement M 0 MW 465 MW 87L line diff to onshore sub · Section 37 route SITE 132 kV GIS — customer-owned · 3,150 A · 40 kA · 87B bus differential CB1 CB2 CB3 CB4 · PW TX1 132/33 kV150 MVA YNd11 TX2 132/33 kV150 MVA YNd11 TX3 132/33 kV150 MVA YNd11 PW TX 132/33 kV(if 132 kV landing) 33 kV SITE BUS — grid-formed by BESS · buses A/B/C, ring normally open −10 MW GRID-FORMING BESS 600 MW / 2,400 MWh 12 × 50 MW / 200 MWh LFP V/f reference · islanding <100 ms 2 × 6-unit strings · NFPA 855 DC arc-flash optical protection 455 MW 33 kV RING MAIN (NOP) RACK POWER — 2,592 × GB300 NVL72 @ 135 kW 11/0.4 kV cast-resin unit substations (24 per 60 MW hall) → overhead busway → rack PSU shelves 800 VDC-ready: halls E–G provisioned for OCP 800 VDC sidecar distribution per the NVIDIA Vera Rubin / DSX reference design Ride-through: rack-level e-caps + BESS grid-forming bus removes the central UPS layer — the battery farm IS the UPS LIFE-SAFETY DIESELS N+1 × 2.5 MVA · 11 kV 48 h fuel · safety loads only Figure — ALY-DC-ELEC-SLD-001 rev DSX-TWIN · conceptual, for review only · protection per IEC 61850 station bus

Operating Modes

Four dispatch states cover every credible combination of wind, grid and storage. Click a card (or the selector above) to drive the diagram.

BESS — the grid-forming heart

600 MW / 2,400 MWh of LFP storage does three jobs at once: it is the campus UPS (no separate UPS layer), the V/f reference that lets the site island in under 100 ms, and a revenue asset dispatched by Constellation against the grid.

Autonomy envelope

600 MW rated discharge4.0 h
500 MW facility peak6.0 h*
455 MW steady (Mode 4)~6.6 h*
405 MW IT-only priority>8 h*

*Includes usable-SOC window and inverter losses at first pass; to be confirmed by cell-level modelling. 3,000 MWh nameplate would firm 6 h at 500 MW — sizing sensitivity carried in SENSE_CHECK.

Grid-forming requirement

Inverters must run V/f (grid-forming), not grid-following — SMA Sunny Central Storage UP, Siemens SINAMICS or Tesla Megapack grid-forming firmware class. Fault contribution 1.2–1.5× rated is the design basis for 33 kV switchgear; droop or isochronous sharing coordinates with the Seagreen infeed.

Safety & separation

NFPA 855 layout with >50 m BESS-to-hall separation, per-container optical DC arc-flash detection tripping DC contactors, dedicated sprinkler tanks, and 2 × 6-unit 33 kV strings to cap fault level and blast-radius of any single event.

Protection & Control

ProtectionLocationSchemeTrips
132 kV bus differentialSite GIS87B low-impedance biased diffCB1–CB3
Transformer differentialTX1–TX387T biased diff + REFHV & LV CBs
33 kV feedersRing + radials50/51 + 50N/51N inverse-time + instFeeder CBs
Islanding detectionGrid incomersROCOF + vector shift + SSEN direct transfer tripCB1, CB2 · <100 ms
Private-wire linePW incomer87L line differential to Seagreen onshore substationCB4
BESS DC arc-flashContainersOptical sensing → DC contactorsDC contactors
Station automationSite-wideIEC 61850 station bus · SEL/Siemens IEDs—
Control hierarchy. L4 Constellation portfolio optimisation (wind forecast, arbitrage, BM) → L3 site EMS / microgrid controller (mode selection, islanding, SOC) → L2 plant controllers (BESS PPC, DCIM, cooling) → L1 field devices. The mode switching you see on this page is the L3 state machine.

Major Equipment Schedule

TagEquipmentRatingQtyLocation
—132 kV GIS panels132 kV · 3,150 A · 40 kA4 baysSite switchyard
TX1–TX3Power transformers132/33 kV · 150 MVA · ONAN/ONAF · YNd113Transformer bays
TX4–TX17Hall distribution transformers33/11 kV · 60 MVA · Dyn1114 (2/hall)Adjacent to halls
—Unit substations11/0.4 kV · 2.5 MVA cast-resin162In-hall
B1–B12BESS blocks, grid-forming50 MW / 200 MWh DC12BESS farm
—Private-wire termination132 or 33 kV + 87L1 bayPW compound
G1–GnLife-safety diesels2.5 MVA · 11 kV · 48 h fuelN+1Generator compound

Standards

BS EN 61936-1 · HV installationsIEC 61850 · substation automation G99 / G100 · grid complianceCUSC · NESO connection code BS EN IEC 62933 · energy storageNFPA 855 · ESS fire safety EN 50600 · DC facilitiesUptime Tier III target
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