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.
Fig. B22: Typical arrangment of switchgear panels for LV metering
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
Fig. B23: Plan view of typical substation with LV metering
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.
