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Outdoor substations

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General rules of electrical installation design
Connection to the MV utility distribution network
Connection to the LV utility distribution network
MV and LV architecture selection guide for buildings
LV Distribution
Protection against electric shocks and electrical fires
Sizing and protection of conductors
LV switchgear: functions and selection
Overvoltage protection
Energy Efficiency in electrical distribution
Power Factor Correction
Power harmonics management
Characteristics of particular sources and loads
PhotoVoltaic (PV) installation
Residential premises and other special locations
ElectroMagnetic Compatibility (EMC)


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. B49Type 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. B50Walk 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. B51Outdoor substations. The three type of design

Fig. B52Two examples of outdoor substations

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. B53Outdoor 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. B54Pole mounted MV/LV substation