Internal MV circuits

The main possible connection configurations are as follows (Fig. D9):

• single feeder, one or several transformers
• open ring, one MV incomer
• open ring, 2 MV incomers

The basic configuration is a radial single-feeder architecture, with one single transformer.
In the case of using several transformers, no ring is realised unless all of the transformers are located in a same substation.
Closed-ring configuration is not taken into account.

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Fig. D9: MV circuit configuration

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For the different possible configurations, the most probable and usual set of characteristics is given in the table on Fig D10.

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	MV circuit configuration
Characteristic to consider	Single feeder	Open ring 1 MV substation	Open ring 2 MV substations
Site topology	Any < 25000m²	Building with one level or several buildings ≤ 25000m²	Several buildings ≥ 25000m²
Maintainability	Minimal or standard	Enhanced	Enhanced
Power demand	Any	> 1250kVA	> 2500kVA
Disturbance sensitivity	Long interruption acceptable	Short interruption acceptable	Short interruption acceptable

Fig. D10: Typical values of the installation characteristics

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Another exceptional configuration: power supply by 2 MV substations and connection of the transformers to each of these 2 substations (MV “double ended” connection).