LV distribution - centralized or distributed layout

Layout

Position of the main MV and LV equipment on the site or in the building.
This layout choice is applied to the results of stage 1.

Selection guide:

As recommended in IEC60364-8-1 §6.3, MV/LV substation location can be determined by using the barycenter method:

• taking into account service conditions: in dedicated premises if the layout in the workshop is too restrictive (temperature, vibrations, dust, etc.)
• Placing heavy equipment (transformers, generators, etc.) close to walls or to main exits for ease of maintenance.

A layout example is given in the following diagram (Fig. D13):

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Fig. D13: The position of the global load barycentre guides the positioning of power sources

Centralized or distributed layout of LV distribution

In centralized layout, each load is connected directly to the power source. (Fig. D14):

Fig. D14: Example of centralized layout with point to point links

In distributed layout, loads are connected to sources via a busway. This type of distribution is well adapted to supply many loads that are spread out, where easy change is requested or future new connection (need of flexibility) (Fig D15):

Fig. D15: Example of distributed layout, with busway

Factors in favour of centralized layout (see summary table in Fig. D16):

• Installation flexibility: no,
• Load distribution: localized loads (high unit power loads).

Factors in favor of distributed layout:

• Installation flexibility: "Implementation" flexibility (moving of workstations, etc…),
• Load distribution: uniform distribution of low or medium unit power loads

	Load distribution
Flexibility (see § 3.6 for definition of the flexibility levels)	Localized loads	Intermediate distribution loads	Uniformly distributed loads
No flexibility	Centralized		Decentralized
Flexibility of design
Implementation flexibility	Centralized	Decentralized
Operation flexibility

Fig. D16: Recommendations for centralized or distributed layout

Centralized distribution gives greater independence of circuits, reducing the consequences of a failure from power availability point of view.

The use of decentralized distribution with busway is a way to merge all the circuits in one: it makes it possible to take into account the diversity factor (ks), which means cost savings on conductor sizing (See fig. D17). The choice between centralized and decentralized solutions, according to the diversity factor, allows to find an economic optimum between investment costs, installation costs and operating costs.

These two distribution modes are often combined.

The main characteristics to consider for implementing LV back-up generator:

Fig. D17: Example of a set of 14 x 25A loads distributed along 34 meters (for busway, Canalis KS 250A)