Utility documents for data center sites: what each one commits

The power position of a data center site is often described by one document, usually a letter, and one number, the megawatts in it. Over the life of a project a utility issues several documents, and each commits it to something different. Five appear on most projects: a capacity letter, a connection offer, a connection agreement, an energisation certificate and a supply contract. Their names vary between utilities and countries, and where one body owns the network and sells the energy, the agreement and the supply contract may be combined. The content of each stage is more consistent than the names. This article sets out what each document commits the utility to, what it leaves open, the risk the owner carries in the difference, and what the owner’s feasibility study should ask for.

The utility and the resilience objective

Uptime Institute’s Tier Standard: Topology treats the engine-generator plant as the primary power source of the data center and the utility as an economic alternative. A weak or interruptible grid therefore does not prevent a Tier objective. It changes the hours the generators run, the fuel stored on site, the emissions permit and the operating cost, and it can set the project programme, because the facility cannot be commissioned at load or operated economically without a permanent supply. The utility documents decide those matters, and they warrant the same technical review as the design. In UBIK’s feasibility studies the utility position is recorded document by document, with an owner and a date against each open item.

Capacity letter

A capacity letter, sometimes called an availability letter or a no-objection letter, states that capacity may be available in an area or at a named substation on the date it was written. It commits the utility to very little: typically no reservation of capacity, no connection date, no voltage, no point of connection and no cost. It may carry a validity period, and another applicant can take the same capacity before the owner applies. The risk is that land is bought, or an investment case approved, on a figure that was never reserved.

At feasibility, the owner should ask whether the letter reserves anything and for how long, which substation and voltage it refers to, which system studies the utility will run on application and how long they take, and what fee or security turns the indication into a formal application.

Connection offer

A connection offer follows a formal application and the utility’s system studies: load flow, short circuit and, where relevant, stability. It states the point of connection, the voltage, the capacity, the scope and cost of the connection works, the programme and the period for which the offer is open for acceptance. It does not reserve capacity until it is accepted and the security is paid, and its date is often conditional on reinforcement works, consents and wayleaves outside the owner’s control. Capacity may be offered in stages, or as non-firm capacity available only when the network permits.

At design stage, the substation, the switchgear and the standby strategy are drawn to the offer. The voltage sets the transformer arrangement and the land take, and the design fault level stated in the offer sets the short-time rating of the owner’s switchgear under IEC 62271. The owner should also ask for the number of incoming circuits and whether they come from separate busbar sections or separate substations, because that decides whether a single utility fault removes the whole supply.

Connection agreement

The connection agreement is the contract. It commits the utility to provide the agreed capacity by the agreed dates, defines the ownership and operational boundary, and sets the technical conditions the owner’s installation must meet: power factor, harmonic emission limits, often referenced to IEC 61000-3-6 or IEEE 519, protection coordination with the utility’s relays, metering and earthing. It rarely commits the utility to continuity of supply, and it often carries no damages payable to the owner for a late connection, while the owner’s obligations, capacity charges and securities, can start on signature. The risk is a fixed obligation on the owner’s side against a conditional one on the utility’s side.

At procurement, the owner should align the orders for transformers and high-voltage switchgear with the agreement’s dates, write its technical conditions into the contractor’s specification, and set the capacity ramp to the IT load ramp rather than to the final capacity.

Energisation certificate

The energisation certificate, or energisation notice, records that the utility has inspected the interface, accepted the test certificates and protection settings it requires, and will energise, or has energised, the point of connection. It commits the utility to supply at the boundary under agreed switching and safety rules. It does not confirm that the full contracted capacity is available, since the first energisation may be limited until reinforcement is complete, and it does not certify the owner’s installation beyond the interface. The risk sits in the commissioning programme: start-up, functional and integrated tests at load need a permanent supply or temporary generation sized for them.

During construction, the owner should obtain the utility’s list of energisation prerequisites early, name the authorised persons for switching on each side of the boundary, and hold a priced temporary power plan against a late energisation.

Supply contract

The supply contract is with the party that sells the energy, which may or may not be the network utility. It commits the supplier to a tariff, a contracted maximum demand, metering, billing and payment terms for a stated period. It does not commit to uninterrupted supply, and interruptions are commonly excluded from its liabilities. The risks are commercial: demand charges and minimum-take clauses on a contracted demand set at the final capacity, and penalties for a power factor outside the agreed band, which in a lightly loaded facility can drift leading because of UPS input filters and cable capacitance.

At energisation, the contracted demand should follow the load ramp, with a written procedure and notice period for increasing it, and the power factor band should be checked against the facility’s expected first-year load.

What the record should contain at close-out

The utility file handed to the operator should contain each document with its date, validity and conditions, and the evidence that each condition was discharged: the accepted offer and the security paid, the signed agreement with its technical schedules, the energisation certificate, and the supply contract with its contracted demand and the procedure to change it.

It should also contain the as-built single-line diagram at the point of connection, the protection settings agreed with the utility, the metering arrangement, the operational boundary and the switching schedule, the utility’s contacts for planned and unplanned outages, and the capacity still to be drawn down under the agreement, with its dates. The owner keeps the file, and the operator works from it for planned outages, demand increases and any later change to the connection.