Market

Data centres

225 / 20 kV substations of several hundred MVA, with redundancy at every level. We carry out the studies and the technical support, from the connection request to energisation.

For a data centre, the connection lead time often weighs on the whole schedule. RTE lists more than 200 projects, nearly 33 GW, waiting for a high-voltage connection, and plans to serve the most advanced projects first (RTE, July 2026). A complete and consistent technical file from the request stage helps keep your place in the queue.

Points of attention

The voltage plan is a frequent problem. With two 225 / 20 kV transformers loaded at half in normal operation and at full load in N-1, the on-load tap changer (OLTC) range must cover the full contractual voltage range of the upstream network. We have already found it insufficient on advanced projects.

On generator backup, the short-circuit current drops sharply and protection set for the grid no longer sees some faults. A dedicated settings group or suitable functions are then needed, and must be verified.

Re-energising a complete data hall means energising dozens of transformers at the same time, with inrush current, a voltage dip and a risk of nuisance tripping. These phenomena are calculated before commissioning.

An HV substation located in the middle of a campus creates an earth potential rise to be controlled with respect to buildings, fences and telecom cables leaving the site.

We work for the operator or the developer, with no ties to equipment suppliers or contractors, or in support of a general contractor.

01What we do

Studies

Load flow, N-1 and voltage plan
Short-circuit, including generator backup operation
HV / MV protection plan
Earthing system and telecom compatibility
Harmonics from UPS units and power supplies
Transformer energisation

Services

Owner's engineering and design review (VISA) of substations
Follow-up of testing and commissioning
Relay configuration and testing

02Examples

Fig. 01Schematic diagram of a 225 / 20 kV point-of-connection substation with two transformers.

Fig. 02Load flow of a 225 / 20 kV substation with three feeders, showing the voltage at the end of each feeder, the power flows and the transformer loading (54 %).Worked example

Fig. 03Protection zones of a 225 / 20 kV substation. Each zone is bounded by its current transformers, and the zones overlap around the circuit-breakers.Schematic diagram

HV switchgear: instrument transformers and post insulators in a substation — Fig. 04HV switchgear, instrument transformers and post insulators.Photo

03Our offer

Usual content of an offer for this type of assignment. The exact scope, deliverables and price are set in the quotation.

Package 1Connection application
Technical data requested by the network operator, checked for consistency, and schematic diagram.
Package 2Design studies
N and N-1 load flow, short-circuit, protection plan, earthing system, harmonics, according to the agreed scope.
Package 3Review of the contractor's studies
Design review (VISA) of execution documents, deviations ranked blocking, major, minor.
Package 4Testing and energisation
Follow-up of factory and site tests, check of settings, attendance at the first energisation.

04How we work

01Connection application
Power, load profile, phasing and schematic diagram, with consistent data, as the network operator asks for them.
02Design studies
N-1 load flow, short-circuit, protection plan, earthing, harmonics from UPS units and power supplies.
03Review of the contractor's studies
Design review (VISA) of execution documents, with deviations ranked by severity.
04Testing and commissioning
Follow-up of factory and site tests, check of settings, first energisation.

05References

Data centre operator

225 kV GIS substation

Design review and review of the studies (VISA). We found deviations on the voltage transformers and on trip circuit redundancy.

General contractor

Protection plan, 240 MVA data centre

Selection of protection functions, current transformer sizing, settings, follow-up of testing through to commissioning.

Data centre, Île-de-France

225 / 20 kV substation

Review of the drawings for the entire substation package against the client's requirements, with the list of major deviations.

Data centre, Île-de-France

Load flow campaign on an ETAP model

Audit of the existing scenarios and sweep of upstream voltage × configurations. The on-load tap changer range of the 225 kV transformers proved insufficient.

Data centre campus

Earthing systems

Earth grid, step and touch voltages, earth potential rise, compatibility with telecom networks.

All references

06Frequently asked questions

Do you work for the project owner or for the contractor?

Both. We prefer to work for the project owner, and we have no ties to any supplier or contractor.

Can you take over a model built by another consultancy?

Yes. We check it first (data, topology, scenarios) before using its results.

Do you cover operation on standby generators?

Yes. We calculate short-circuit currents in backup mode, adapt the settings and study generator starting and load pick-up.