Substations
Compact substations
One prefabricated enclosure carrying the medium voltage switchgear, the transformer and the low voltage distribution, delivered as a unit and set on a prepared foundation. It is also known as a mini substation or a kiosk substation.
- Standard
- IEC 62271-202AC prefabricated substations, operating voltage up to 52 kV
- Operation
- from outside, or walk inthe standard covers both
- Transformer
- commonly in the distribution rangerating set by the load
- Medium voltage
- commonly a ring main unitconfiguration set by the network
- Enclosure
- concrete, steel or compositeset by site and specification
A compact substation arrives complete, so the site work comes before delivery. Three things decide whether the delivery date holds: a prepared foundation, cable ducts in the right positions, and access for the delivery vehicle and the lifting equipment.
The enclosure is type tested with its contents, so changing the equipment once manufacture has started costs money. Fix the transformer rating, the ring main unit configuration and the low voltage schedule before you order.
What gets specified
| Parameter | Typical options | What decides it |
|---|---|---|
| Transformer inside | Rating, voltage pair, liquid immersed or cast resin | The load, and the heat the enclosure has to let out at that rating |
| Medium voltage switchgear | Ring main unit, commonly two ring switches and a transformer feeder | How the station is looped into the cable ring |
| Low voltage distribution | Incomer and a schedule of outgoing ways | The feeders that leave the station |
| Enclosure | Precast concrete, steel or composite | Road transport limits, the look of the site and the owner's preference |
| Operation | Through external doors, or walk in | Operating practice and climate |
| Internal arc classification | As tested for the complete station | Where the public and operators can stand while it is energised |
| Metering and auxiliaries | Metering position, auxiliary supply, remote signalling | The network operator and the owner |
UK and Gulf rules for a station
In the UK, ENA EREC S40, Issue 2 of September 2026, is the engineering recommendation for prefabricated substations, covering switchgear up to 36 kV and transformers up to 2000 kVA. Where the station belongs to a distributor or generator, ESQCR regulation 11 requires it to be enclosed where necessary and live equipment in the open air to be fenced or walled to at least 2.4 m. A notice gives the location, the owner or operator and a telephone number that is constantly attended.
In Qatar, Kahramaa's substation guidance allows an outdoor station for a load of up to 1,600 kVA where no second transformer is foreseen, and requires an indoor substation once there are two or more.
Applicable standards
| Standard | What it covers |
|---|---|
| IEC 62271-202 | The station as a whole: cable connected, prefabricated, up to and including 52 kV, operated from inside or outside |
| IEC 62271-200 | The ring main unit or panels inside it |
| IEC 61439-1 and IEC 61439-2 | The low voltage board inside it |
| IEC 60076-1 | The transformer it carries |
Evidence particular to a prefabricated station
| Document | What to check |
|---|---|
| Type test report of the station | That it covers the enclosure with the transformer rating and switchgear now offered |
| Lifting data | The mass of the complete station and its lifting points, for the crane plan |
| Duct and foundation drawing | Where each cable must enter, before the concrete is poured |
What a compact substation request needs
- The transformer rating, voltage pair and construction
- The ring main unit functions and how the station loops into the ring
- The low voltage incomer and the outgoing ways
- Concrete, steel or composite, and any requirement on appearance
- Access for the delivery vehicle and the crane
Specification template
Fill it in on screen or by hand, then upload it with your request.
Questions buyers ask
Can the transformer inside a compact station be changed later?
Physically, sometimes. The type test covers the station with the equipment it was tested with, so a different transformer can fall outside what the test proves. Settling the rating before the order costs less.
Is a compact substation the same as a mini substation?
Yes, mini substation and kiosk substation are other names for the same thing: switchgear, transformer and low voltage board in one prefabricated enclosure. The standard that defines it is IEC 62271-202.