Power Conversion & HV Connection
The electrical spine of the site - conversion plant, transformers, switchgear, protection, earthing and the cable network that carries power out to the network operator's connection point.
Last updated 2026-09-06
Typical duration
Typically 6-14 weeks on a scheme of a few tens of megawatts, though the network operator's outage and witnessing dates usually dictate the critical path rather than the installation labour.
What is Power Conversion & HV Connection?
Batteries store and release direct current. The network runs on alternating current at high voltage. Everything in this stage exists to bridge that gap and to do it safely, in both directions, thousands of times a year. The chain is straightforward to describe: direct current cabling from the enclosures to the conversion plant, conversion plant turning direct current into alternating current and back again, step-up transformers raising the voltage, switchgear collecting the circuits together, and a single connection point where the site meets the network. Protection, control, metering and communications sit across the whole chain, watching it and deciding in a fraction of a second when to disconnect.
Physically it looks like a compound of skids and kiosks. Conversion plant and transformers are often supplied as combined power blocks, delivered and set much like the battery enclosures, which keeps the site work down to positioning, cabling and terminating. Switchgear and protection panels live in a kiosk or a small building, sometimes with the control and communications equipment alongside. Oil-filled plant needs bunding and containment. Everything needs earthing, and the earthing grid that went in during the civils gets bonded to every piece of apparatus as it lands. The bulk of the labour is cable: pulling it, laying it, jointing it and terminating it, done by qualified jointers to procedures rather than by general labour with a knife.
The connection itself belongs to the network operator, and that changes the tone of the work. The operator sets the interface, the point of connection, the metering, the protection requirements and the tests that must be passed before anything is closed onto its system. It may build the connection bay itself, or accept works built by the developer to its requirements and then adopt them. Either way, outages have to be booked, witnessed inspections have to be arranged, and the site works to the operator's calendar rather than its own. A well-run project treats those dates as immovable and works backwards from them, because a missed witness slot can cost more programme than a month of bad weather.
Compare the methods at a glance
When and why is Power Conversion & HV Connection used?
This stage follows the enclosures because the direct current cabling has to terminate on something at both ends, but in practice it overlaps heavily - the conversion plant and switchgear are often set while the battery rows are still being lifted, and the cable pulls chase both. It is the stage that turns a field of expensive boxes into a power station. The reason the arrangement looks the way it does is efficiency and standardisation: a factory-built power block arrives tested, a repeated circuit design can be built and checked the same way every time, and a single collection point keeps the interface with the network operator simple. The commercial logic is blunt. Revenue depends on being able to import and export at the agreed capacity on the agreed date, so the design, the protection settings and the metering all have to satisfy the operator's requirements before anything is energised. Attempting to negotiate that at the end never works. The sequence within the stage is fixed by safety: cable routes and earthing are proved before covering, dead testing is completed before anything is energised, and settings are applied and independently verified before the plant is asked to protect itself. Every specification here - cable sizes, protection settings, clearances, earthing arrangement - comes from the designer and the operator, and site's task is to build it exactly as issued and prove that it did.
Types of Power Conversion & HV Connection
Explore each method in depth - benefits, limitations, plant and quality control on its own page.
Integrated power blocks
Conversion plant, step-up transformer and associated switchgear supplied as one factory-tested skid. Fewest site interfaces and the fastest to install, which is why most grid-scale schemes now use them, but the layout is fixed by the supplier and awkward plots have to work around it.
Explore this methodSeparate conversion plant and transformers
Conversion equipment and transformers procured and set as separate items and cabled together on site. More flexible for constrained or irregular sites and for mixing suppliers, at the cost of more site cabling, more terminations and more interfaces to prove.
Explore this methodModular or distributed conversion
Smaller conversion units spread through the rows rather than concentrated in one compound, shortening the direct current runs and keeping a fault in one unit from taking out a large block of capacity. More items to install and maintain, and more control points to commission.
Explore this methodSite substation and connection compound
The high voltage end of the site: collection switchgear, protection and metering, and either a new customer substation or a new bay within an existing one. Built to the network operator's requirements and inspected on its terms, and usually the item with the longest lead time on the whole project.
Explore this methodBest suited for
- Grid-scale schemes importing and exporting at network voltage under an agreed connection
- Co-located sites sharing a single connection point with solar or wind generation
- Projects providing fast response services, where the conversion plant and controls are the product
- Connections that defer or replace conventional network reinforcement
Power Conversion & HV Connection: step by step
- 1
Step 1: Set the conversion plant, transformers and switchgear
The heavy electrical items are delivered and set on the bases prepared during the civils, using the same lift planning discipline as the battery enclosures. Position and orientation matter because cable entries, access doors, ventilation and maintenance clearances are all fixed by the equipment and by the design layout. Oil-filled plant is set within its bund, and the containment is checked as part of the installation rather than being treated as a civils leftover. Units are levelled, fixed down as the design requires, and bonded to the earthing system. Any transport restraints and desiccant arrangements are dealt with according to the manufacturer's instructions, and equipment that will stand for weeks before energisation is protected against moisture in the way the manufacturer specifies.
- 2
Step 2: Complete the earthing and bonding system
The buried earthing grid installed during the civils is now connected to everything above ground: enclosures, conversion plant, transformer tanks, switchgear, kiosks, fencing where the design requires it, and any exposed metalwork identified by the designer. Connections are made using the specified method, protected against corrosion, and left accessible where the design says they should be testable. The earthing arrangement is one of the primary safety systems on a high voltage site - it is what keeps touch and step voltages within the values the designer has calculated during a fault - so it is inspected, tested and recorded formally rather than as a tick in a box. Any addition or alteration made later gets recorded on the earthing as-built, because the drawing is what the operator will rely on for decades.
- 3
Step 3: Install the direct current and low voltage cabling
Cable is pulled from the battery enclosures to the conversion plant along the routes established during the civils, with the auxiliary supplies that feed cooling, controls, lighting, small power and security run alongside. Drums are set up so cable is pulled with the right radius and without dragging, rollers and winches are used where the pull is long, and the design tension and bend limits are respected because a cable damaged inside its insulation gives no sign of it until it fails in service. Cable is supported, cleated and labelled as the design requires, with segregation between systems as specified. Terminations are made to the manufacturer's method, recorded, and left ready for the dead testing that follows.
- 4
Step 4: Install and joint the high voltage cabling
The medium and high voltage cabling between the power blocks, the collection switchgear and the connection point is the most specialised installation on the site. It is pulled into the ducts and trenches laid earlier, with the bedding, surround, marker tape and separation the design calls for, and any joints made in clean, dry, controlled conditions - usually inside a jointing shelter - by jointers qualified for that cable and that jointing system. Terminations are made the same way. Phasing is established and recorded as the cable goes in, not assumed from the drum markings. Route positions are surveyed as-built before backfill, because a high voltage cable whose position is only approximately known is a hazard for every future excavation on the site.
- 5
Step 5: Install protection, control, metering and communications
The protection and control panels are installed and wired, along with the metering the network operator requires and the communications that will carry data off site. Settings are loaded from the approved schedule issued by the protection engineer - never from a previous project or a default - and every setting is checked against that schedule by someone other than the person who applied it. Current and voltage transformer circuits are wired and proved, interlocks and trip circuits are connected, and the control system is configured so that every command and every alarm points at the item it is actually connected to. Labelling across the whole installation is completed at this stage, because mislabelled apparatus is a safety problem, not a cosmetic one.
- 6
Step 6: Carry out dead testing across the installation
Before anything is energised, the whole installation is tested while it is safely dead. That covers insulation testing of cables and apparatus, continuity, phase identification and phasing checks, earth continuity and earthing system measurements, transformer checks, functional testing of trip and interlock circuits, and injection testing of the protection to confirm that it operates as the settings say it should. Test equipment is calibrated and the certificates are current. Results are recorded on the test sheets as they are taken, signed and kept, because these documents are the evidence the operator and the client rely on when deciding whether the site may be connected. Anything that fails is put right and retested rather than noted and moved past.
- 7
Step 7: Complete the network operator's interface works
The connection point is prepared to the operator's requirements, whether that is a new customer substation, a new bay at an existing site, or a cable terminated ready for the operator to make its own connection. Documentation is submitted in the operator's format and to its timetable: design approvals, test results, settings, metering details and the compliance evidence it requires. Outages and witness dates are booked well ahead. Works on or near the operator's existing apparatus happen under its control, with its permits and its people, and the project team has no discretion in that. This is the stage most likely to expose an assumption made months earlier, which is why experienced teams keep the operator engaged from design onwards rather than presenting it with a finished site.
- 8
Step 8: Complete records, labelling and the pre-energisation review
The installation is walked and reviewed as a whole before energisation is even discussed: labelling correct and complete, covers and barriers fitted, access and escape routes clear, bunds and containment finished, temporary works removed, cable routes recorded, and test documentation collated into a coherent pack. Any deviation from the issued design is captured as an as-built change with the designer's agreement, not left in someone's memory. Isolation points, operating restrictions and the site's safety rules are set out so that the people carrying out commissioning inherit a defined, documented installation. A clean pre-energisation review is what makes the next stage an orderly sequence rather than a series of surprises.
Plant & equipment
- Mobile cranes and telehandlers for setting power blocks, transformers and kiosks
- Cable drum trailers, stands, winches and roller sets for long cable pulls
- Jointing shelters, cleaning and preparation kit for high voltage joints and terminations
- Calibrated crimping, cutting and torque tooling for terminations
- Insulation and continuity test sets, earth testers and primary and secondary injection kits
- Cable identification and route tracing equipment
- Thermal imaging cameras for post-energisation inspection
- Oil handling, sampling and spill containment equipment for filled plant
Quality control & testing
- Cable routes, supports and segregation installed as the design shows and recorded before covering
- Pulling tensions and bend radii kept within the cable manufacturer's limits
- High voltage joints and terminations made by qualified jointers, with named records for each one
- Terminations tightened with calibrated tooling to the manufacturer's stated requirement and recorded
- Earthing system tested and results recorded against the designer's requirements
- Protection settings applied from the approved schedule and independently verified by a second person
- All test results captured on calibrated instruments with current certificates and traceable serial numbers
- Labelling, phasing and as-built drawings completed and checked before energisation is requested
Safety watchpoints
- High voltage apparatus - work only under the site's safety rules, with permits issued by an appointed authorised person
- The direct current side is energised from the moment the batteries are connected and cannot be switched off in the way a supply can
- Arc flash risk during work on or near switchgear, with the assessment and protective equipment set by the project
- Work on or adjacent to the network operator's live apparatus, which happens under the operator's control and permits
- Heavy cable pulls, drum handling and trapping injuries during installation
- Transformer handling, oil spillage and the environmental controls that go with it
- Excavation and reinstatement over live cable routes once part of the site is energised
- Clear isolation, lock-off and communication arrangements when parts of the site are live and parts are still being built
Common defects to hunt
- Loose or poorly made terminations creating hot joints that only show up on a thermal survey
- Cable damaged during pulling and installed anyway, failing in service months later
- Earthing continuity not proven before backfill, leaving an unverifiable safety system
- Protection settings applied but never independently checked against the approved schedule
- Phasing or labelling errors that turn a straightforward switching operation into an incident
- Water ingress at glands, kiosk bases and cable entries on an exposed site
- Metering and communications not built to the network operator's requirements, failing its inspection
- Missing or disorganised test records, forcing whole sections of the installation to be retested
How long does Power Conversion & HV Connection take?
Typical duration: Typically 6-14 weeks on a scheme of a few tens of megawatts, though the network operator's outage and witnessing dates usually dictate the critical path rather than the installation labour..
Related processes
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- Commissioning & Energisation
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- Modular or distributed conversion - method
- Site substation and connection compound - method
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