Outdoor substations

From Electrical Installation Guide

Outdoor substations with prefabricated enclosures

The prefabricated outdoor MV/LV substations (see Fig. B49) comply with IEC 62271-202 standard.

  • A type tested prefabricated outdoor substation is subjected to tests and verifications dedicated to:
    • Degree of protection
    • Temperature class
    • Non-flammable materials
    • Mechanical resistance of the enclosure
    • Sound level
    • Insulation level
    • Internal arc withstand
    • Earthing circuit
    • Retention of oil
    • Operation of the substation.

Main benefits:

The prefabricated substations provide a particularly interesting and optimized solution regarding:

  • Delivery time
  • Construction works
  • Erection works
  • Commissioning
  • Total cost.
Fig. B49 – Type tested substation according to IEC 62271-202

IEC 62271-202 standard defines requirements for two types of outdoor prefabricated substations (see Fig. B50:)

  • Walk-in type substation
  • Non walk-in type substation.
Fig. B50 – Walk in and non-walk in type substations

The substations may be situated at ground level, half buried or completely buried (underground substation), resulting in three types of design (see Fig. B51 and Fig. B52).

Fig. B51 – Outdoor substations. The three type of design

Outdoor substation without enclosure

(see Fig. B53)

This kind of outdoor substations based on weatherproof equipment is commonly used in countries such as UK and India for example.

These substations are generally included in MV rings and include:

  • Two functional units dedicated to the connection of the substation to the ring
  • One functional unit for the supply and the protection of the MV/LV power transformer generally done by a circuit breaker unit
  • One single MV/LV Power transformer
  • One LV distribution panel.

The transformer and the LV panel can be installed in dedicated outdoor type housing.

Fig. B53 – Outdoor substation without enclosure

Pole mounted substation


These substations are mainly used for the supply of isolated rural consumers from MV overhead lines.


This type of substation includes (see Fig. B54):

  • A single pole mounted MV/LV power transformer that is, according to the local rules associated or not with:
    • A load break switch
    • A set of three fuses
    • A set of three surge arrestors
  • A low voltage circuit breaker
  • An earthing electrode realized at the bottom of the pole supporting the equipment.

The location of the substation must allow easy access of the personnel and handling equipment.

Fig. B54 – Pole mounted MV/LV substation