Indoor substation

Conception

Figure B22 shows a typical equipment layout recommended for a LV metering substation.
Remark: the use of a cast-resin dry-type transformer does not need a fireprotection oil sump. However, periodic cleaning is needed.

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Fig. B22: Typical arrangment of switchgear panels for LV metering

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Service connections and equipment interconnections

At high voltage

Connections to the MV system are made by, and are the responsibility of the utility

• Connections between the MV switchgear and the transformers may be:

  - By short copper bars where the transformer is housed in a panel forming part of the MV switchboard
  - By single-core screened cables with synthetic insulation, with possible use of plug-in type terminals at the transformer

At low voltage

• Connections between the LV terminals of the transformer and the LV switchgear may be:

  - Single-core cables
  - Solid copper bars (circular or rectangular section) with heat-shrinkable insulation

Metering (see Fig. B23)

• Metering current transformers are generally installed in the protective cover of the power transformer LV terminals, the cover being sealed by the supply utility
• Alternatively, the current transformers are installed in a sealed compartment within the main LV distribution cabinet
• The meters are mounted on a panel which is completely free from vibrations
• Placed as close to the current transformers as possible, and
• Are accessible only to the utility

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Fig. B23: Plan view of typical substation with LV metering

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Earthing circuits

The substation must include:

• An earth electrode for all exposed conductive parts of electrical equipment in the substation and exposed extraneous metal including:

  - Protective metal screens
  - Reinforcing rods in the concrete base of the substation

Substation lighting

Supply to the lighting circuits can be taken from a point upstream or downstream of the main incoming LV circuit-breaker. In either case, appropriate overcurrent protection must be provided. A separate automatic circuit (or circuits) is (are) recommended for emergency lighting purposes.
Operating switches, pushbuttons, etc. are normally located immediately adjacent to entrances.
Lighting fittings are arranged such that:

• Switchgear operating handles and position indication markings are adequately illuminated
• All metering dials and instruction plaques and so on, can be easily read
  

Materials for operation and safety

According to local safety rules, generally, the substation is provided with:

• Materials for assuring safe exploitation of the equipment including:

  - Insulating stool and/or an insulating mat (rubber or synthetic)
  - A pair of insulated gloves stored in an envelope provided for the purpose
  - A voltage-detecting device for use on the MV equipment
  - Earthing attachments (according to type of switchgear)

• Fire-extinguishing devices of the powder or CO₂ type
• Warning signs, notices and safety alarms:

  - On the external face of all access doors, a DANGER warning plaque and prohibition of entry notice, together with instructions for first- 
    aid care for victims of electrical accidents.