Functions of a substation with LV metering

A consumer substation with LV metering is an electrical installation connected to a utility supply system at a nominal voltage of 1 kV - 35 kV, and includes a single MV/LV transformer generally not exceeding 1,250 kVA.

The different functions of the substation are:

The substation
All component parts of the substation are located in one room, either in an existing building, or in the form of a prefabricated housing exterior to the building.

Connection to the MV network
Connection at MV can be:

• Either by a single service cable or overhead line, or
• Via two mechanically interlocked load-break switches with two service cables from duplicate supply feeders, or
• Via two load-break switches of a ring-main unit
  

The transformer
Since the use of PCB⁽¹⁾ - filled transformers is prohibited in most countries, the preferred available technologies are:

• Oil-immersed transformers for substations located outside premises
• Dry-type, vacuum-cast-resin transformers for locations inside premises, e.g. multistoreyed buildings, buildings receiving the public, and so on...

(1) Polychlorinated biphenyl

Metering
Metering at low voltage allows the use of small metering transformers at modest cost.
Most tariff structures take account of MV/LV transformer losses.

LV installation circuits
A low-voltage circuit-breaker, suitable for isolation duty and locking off facilities, to:

• Supply a distribution board
• Protect the transformer against overloading and the downstream circuits against short-circuit faults.

Simplified electrical network diagram
The diagram (Figure B10) shows:

• Methods for connecting to the network (4 options):

  - Spur network or single-line service
  - Provisional network (can be transformed into a loop)
  - Parallel feeders service
  - Loop or ring-main service

• MV protection and MV/LV transformation methods
• LV metering and LV general isolation methods
• LV protection and distribution methods
• Zones accessible to different parties 

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Fig. B10: Consumer substation with LV metering

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