Transformer capacity
The transformer is rarely the tightest constraint and is usually the one that sets the date.
What runs out
Usable secondary capacity after the site's derating policy and at the redundancy the hall is sold on.
The relation that governs it
Required MVA ≈ (racks × rack kW × PUE) / 1000 / pf, at N+1 or 2N as the hall is contracted. Harmonic content from GPU rectifier loads derates a standard unit further.
Worked example
What transformer capacity do 20 NVIDIA GB300 NVL72 racks need?
20 × 135 kW × PUE 1.20 / 1000 / 0.95
3.41 MVA before redundancy
At N+1 the installed capacity has to carry that with one unit out of service.
Reproducible by hand. A page that asks you to trust a number has taught you nothing.
How to tell whether it binds in your hall
Sum your existing IT load and the new load at your expected PUE, divide by 0.95, and compare against installed capacity with one unit out of service. If the margin is thin, check lead time before you check price.
What relieves it
Additional or replacement transformer capacity, and the switchgear that comes with it.
What that relief costs beyond money
Lead times of 120–160+ weeks have been reported for power transformers. This is the item most likely to set the energisation date for the whole retrofit, and every week of it is a week of contracted power earning nothing.
Indicative relief lead time
52–160 weeks
European retrofits. The schedule, not the capex, usually decides.
How we currently price this relief
E0
A placeholder with a −50%/+100% band, not a price. It is replaced by a quotation the first time we tender this relief on a real project.
The mistake we actually see
Treated as a capex line when it is a schedule line. A cheaper transformer eighteen months later is the expensive one.
Basis
- — Reported European transformer lead times, 2025–2026.
These usually travel together
Does this one bind in your hall?
Seven numbers you already know, all thirteen constraints evaluated, and the one that stops you first named with its basis in engineering units. Free.