Prefabricated Substation (Concrete Kiosk): IEC 62271-202 Design Guide
prefabricated substation: A prefabricated substation houses the medium voltage switchgear, distribution transformer and low voltage panel in a factory built concrete enclosure, delivered to site as a single type tested compact distribution unit.
Contents
From industrial estates and residential developments to solar farms and infrastructure projects, a prefabricated substation is the fastest way to establish distribution without constructing a building on site. But a kiosk is not merely a concrete box: under IEC 62271-202 it is a type tested product with defined temperature class, degree of protection, internal arc behaviour and mechanical strength. Choosing the right class determines operating quality for years.
What a prefabricated substation is
IEC 62271-202 covers high voltage to low voltage prefabricated substations. The enclosure, MV switchgear, transformer, LV panel and internal connections are assessed as one type tested system. This differs fundamentally from components assembled on site, because the tests address the behaviour of the whole. Two basic architectures exist: walk-in, with an internal corridor, and non walk-in, with external access only.
Temperature class and ventilation
The most critical enclosure parameter is the temperature class. Depending on how much the transformer losses raise the internal temperature above ambient, the class is declared as 5 K, 10 K, 15 K, 20 K, 25 K or 30 K. A lower class means a larger ventilation area and usually a larger enclosure for the same transformer rating. The class is valid only for the tested loss value, so uprating the transformer requires re-verification.
Internal arc rating and personnel safety
The IAC classification ensures that an arc inside the kiosk does not endanger personnel outside. Accessibility type A or B is declared together with the accessible faces F for front, L for lateral and R for rear; IAC-AB 16 kA 1 s is a typical requirement. Pressure relief paths, door latching and discharge directions must be implemented exactly as defined in the test report.
Layout, cable entries and earthing
| Parameter | Typical value | Effect on selection |
|---|---|---|
| Temperature class | 10 K to 30 K | Ventilation area and enclosure size |
| Internal arc class | IAC-A/AB 16 to 20 kA 1 s | Clearance distances and discharge direction |
| Degree of protection | IP23D to IP34D | Dust, rain and finger protection |
| Architecture | Walk-in or non walk-in | Maintenance access and footprint |
| Transformer rating | 400 to 2500 kVA | Losses, temperature class and breaker choice |
Internally the MV compartment, transformer compartment and LV compartment are separated. Cables enter through a bottom trench whose cross section, bending radius and cleating arrangement are resolved in advance. Earthing works on two levels: the kiosk structure bond and the site earthing grid. Step and touch voltages are brought below limits with a ring conductor around the kiosk and, where necessary, driven rods.
Transport, installation and commissioning
Kiosks travel as one piece or in modules; lifting points, crane capacity and ground bearing capacity are calculated in advance. The plinth is prepared with drainage and at a level that avoids flooding, and cable trenches are placed before the kiosk is set down. Commissioning records transformer oil level, MV switchgear interlocks, free ventilation openings, earth continuity measurements and LV panel functional tests.
Key takeaways: prefabricated substation
- A kiosk is a type tested system — compliant components do not automatically make a compliant whole.
- Temperature class follows transformer losses — uprating the transformer requires re-verification.
- State the IAC class with its accessible faces — a kA figure on its own is not a specification.
- Resolve trench and plinth early — retrofitting on site is both costly and risky.
- Standard source — IEC publication catalogue: iec.ch.
Frequently asked questions
Should a concrete kiosk or a sheet steel monoblock be chosen?
Concrete performs better for fire behaviour, sound insulation, vandal resistance and climate durability, while sheet steel is lighter and quicker to transport. Concrete dominates urban and permanent installations; steel is common for temporary or remote sites.
Can a dry type transformer be used inside a kiosk?
Yes. A dry type unit reduces oil containment and fire separation requirements, but usually needs more cooling air at the same rating. The temperature class calculation must therefore be repeated.
Can a kiosk be extended later?
Only to a limited extent. Adding a compartment is feasible in a modular design, but type test validity and internal arc discharge paths may be affected. If growth is likely, select the kiosk for that scenario from the outset.
Related articles
- What is a Medium Voltage (MV) Switchgear? Metal-Clad and RMU Switchgear.
- Dry-Type or Oil-Immersed? Distribution Transformer Selection
- Metering Panel: Grid Connection, Sealing and Measurement Accuracy
- All technical articles
Planning a turnkey prefabricated substation for your site? Devpan defines the temperature and internal arc class for your transformer rating and engineers the MV and LV layout with you. Related Devpan solution: medium voltage switchgear.
