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A 2 500 kVA transformer is substation territory. At this rating the unit stops being an item on an equipment list and becomes a civil works item: a foundation, oil containment, a delivery route that can take the weight, and a protection scheme that has to be designed with it.
This page covers what changes at this size, what has to be specified, and what the site has to have ready before the unit can be set.
What changes above roughly 2 000 kVA
Three things stop being routine at this rating, and they are what move the schedule when they are discovered late.
- Delivery and setting. At seven tonnes or more the unit needs a route survey, a crane or a heavy lifter, and a foundation designed for the point loads. The pad is usually the longest lead item.
- Oil containment and fire separation. The volume of oil puts the unit into a different category with most fire authorities, which means containment, separation and sometimes a firewall have to be designed rather than assumed.
- Protection and monitoring. Confirm the devices required for the selected transformer construction, such as temperature indication, pressure relief and any applicable gas relay. The protection study and manufacturer design determine the package, not the kVA rating alone.
Specifications
Configuration reference
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| Parameter | Typical value | What it depends on |
|---|---|---|
| Rated power | 2 500 kVA (ONAN), higher with ONAF | Load profile and diversity factor |
| Type | Oil-immersed, ONAN or ONAF | Outdoor substation duty at this rating |
| Primary voltage | Up to 34.5 kV | Your utility supply or generator voltage |
| Secondary voltage | 480Y/277 V, 600 V or 4.16 kV | Plant or collection voltage |
| Phases and frequency | Three-phase, 60 Hz | Local network standard |
| Impedance voltage | Typically 6.5 percent | Prospective fault level and parallel operation |
| Vector group | Dyn11, YNd11 or as specified | Parallel operation, harmonics and earth faults |
| Tap changer | Off-circuit or on-load, plus or minus 2 x 2.5 percent | Voltage regulation requirement |
| Cooling | ONAN, with ONAF stage for overload | Loading profile and ambient conditions |
| Losses | Specify applicable efficiency requirements and measured load/no-load losses | Transformer scope, destination market and delivery requirements |
| Protection | Confirm temperature, pressure and gas-protection devices for the selected design | Transformer construction and protection study |
| Compliance documents | Confirm applicable transformer standards and required third-party documents | Exact design, utility specification and inspection requirements |
| Approximate weight | 7 000 to 8 500 kg | Final type and options |
Figures are selection references. Confirm the final ratings, dimensions, available certifications and warranty against the current datasheet and written proposal for the selected model or system.
What arrives in a typical order
- The transformer, filled and routine-tested, with the tap changer set and verified.
- Routine test report for the specific unit to IEEE C57 or IEC 60076.
- Dimensional drawing with the foundation loads, the jacking and lifting points, and the oil volume.
- Wiring diagram, protection device list and the recommended settings.
- Installation, oil handling and maintenance documentation.
The medium-voltage switchgear, the protection relays and the low-voltage board are quoted on the same order when the project needs them, so the fault rating and the discrimination study are settled once.
Where a 2 500 kVA unit usually goes
- Utility and grid-connected substations, stepping between distribution and collection voltage.
- Large industrial plants with a dedicated substation and a substantial continuous load.
- Utility-scale solar and storage, as the main step-up unit for a block.
- Generator step-up duty where the unit has to match the generator voltage and the protection scheme.
What the site has to provide
- A foundation designed for the point loads, built to the drawing we issue with the order.
- Oil containment and the separation distances your fire authority requires.
- A surveyed delivery route and the lifting equipment at the far end of it.
- Termination clearance and access on both sides, and room for future maintenance.
Sizing notes before you order
- Confirm the natural and forced-air ratings, fan power and thermal design if ONAF is proposed. Use only the manufacturer documented rating and permitted loading profile; fans do not establish a generic overload allowance.
- Confirm the impedance against the fault study. At this rating the fault current it allows is what sizes everything downstream.
- Specify the tap changer type from the voltage regulation you actually need. On-load is justified where the supply varies; off-circuit is cheaper and adequate where it does not.
- State losses as separate load and no-load figures and evaluate on lifetime cost. At this size the no-load loss alone runs continuously for decades.
Documentation to confirm for your order
- Routine test report for the specific unit, including the measured losses.
- Foundation drawing with point loads, lifting and jacking points, and the oil volume.
- Wiring diagram, protection device list and recommended settings.
- Installation, oil sampling and maintenance documentation, and warranty terms.
Questions buyers ask
ONAN or ONAF?
ONAN uses natural oil and air circulation; ONAF adds forced-air cooling. Confirm the manufacturer ratings, fan arrangement and permitted thermal loading for the selected design before comparing it with a larger transformer.
Do we need an on-load tap changer?
Where the supply voltage varies enough to affect the plant, yes. Where it does not, an off-circuit tap changer is cheaper and has fewer parts to maintain. The decision follows the voltage you actually see, not a specification habit.
How is the impedance chosen?
From the prospective fault level and from whether the unit will run in parallel with others. Typical values are 6 to 7 percent at this rating. Lower impedance improves regulation but raises the fault current everything downstream has to withstand.
What does the foundation need to be designed for?
The point loads at the wheels or the base, plus the oil containment. We issue the drawing with the loads marked as part of the order, and the pad is usually the item that decides the date.
How long does it take?
Engineered ratings are built to your specification and quoted with a firm date. At this size the schedule is usually driven by the foundation and the delivery route rather than by the build.
What to send us
Send the primary and secondary voltages, the load profile, whether the unit will run in parallel, and your target date. We come back with the rating, the impedance recommendation, the protection list and a firm build date.
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