Outdoor substations

Outdoor substation with prefabricated enclosures

A prefabricated MV/LV substation complying with IEC 62271-202 standard includes :

• equipment in accordance with IEC standards
• a type tested enclosure, which means during its design, it has undergone a battery of tests (see Fig. B24):

  - Degree of protection
  - Functional tests
  - Temperature class 
  - Non-flammable materials
  - Mechanical resistance of the enclosure
  - Sound level
  - Insulation level
  - Internal arc withstand
  - Earthing circuit test
  - Oil retention,…

Fig. B24: Type tested substation according to IEC 62271-202 standard

Main benefits are :

• Safety:

  - For public and operators thanks to a high reproducible quality level

• Cost effective:

  - Manufactured, equipped and tested in the factory

• Delivery time

  - Delivered ready to be connected.

IEC 62271-202 standard includes four main designs (see Fig. B25)

• Walk-in type substation :

  - Operation protected from bad weather conditions

• Non walk-in substation

  - Ground space savings, and outdoors operations

• Half buried substation

  - Limited visual impact

• Underground substation

  - Blends completely into the environment.

                        [a]                                                               [b]

Fig. B25: The four designs according to IEC 62271-202 standard and two pictures [a] walk-in type MV/LV substation; [b] half buried type MV/LV substation

Outdoor substations without enclosures

(see Fig. B26)
These kinds of outdoor substation are common in some countries, based on weatherproof equipment exposed to the elements.
These substations comprise a fenced area in which three or more concrete plinths are installed for:

• A ring-main unit, or one or more switch-fuse or circuit-breaker unit(s)
• One or more transformer(s), and
• One or more LV distribution panel(s).

Fig. B26: Outdoor substations without enclosures

Pole mounted substations

Field of application
These substations are mainly used to supply isolated rural consumers from MV overhead line distribution systems.

Constitution
In this type of substation, most often, the MV transformer protection is provided by fuses.
Lightning arresters are provided, however, to protect the transformer and consumers as shown in Figure B27.

General arrangement of equipment
As previously noted the location of the substation must allow easy access, not only for personnel but for equipment handling (raising the transformer, for example) and the manœuvring of heavy vehicles.

Fig. B27: Pole-mounted ransformer substation