What is the radial scheme of power distribution

Design of the LV circuits

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Essential configuration options (see Fig.D17 to Fig.D24):

Radial configuration with a single feed line

This simplest of all configurations is used as a reference. All consumers are connected to a single source. This configuration provides the minimum level of availability. If the power supply source fails, there is no redundancy.

Fig.D17Configuration with radial single line

Parallel feed

The power supply is provided by 2 distribution transformers connected to the same HV line. If the distribution transformers are close together, they generally feed in parallel to the same LVMD.

Fig.D18Parallel feed

In parallel with two NSHV systems

To increase availability in the event of a power outage or maintenance work on one of the distribution transformers, the LVMD can be divided into 2 parts with a coupling switch. This configuration generally requires an automatic tie switch.

Fig. D19Parallel configuration with two LVM systems and switchover option via coupling switch

Switchgear not authorized to substitute network (simple connection with disconnection option)

A number of non-critical circuits can be connected to switchgear specially designed for this purpose. The connection to the LVHV can be interrupted if necessary (overload, generator operation, etc.)

Fig.D20Switchgear not authorized to substitute network

Coupled switchgear

Spatially separated transformers can be connected via busbar trunking systems. Critical consumers are supplied by one or more transformers. The security of supply is improved because the supply of the consumer is secured in the event of failure of a source.

Fig. D21Coupled switchgear

Redundancy options

  • Complete: Each transformer can supply the entire system.
  • Partly: Each transformer can only supply part of the system. In this case, some of the consumers must be switched off (load shedding) if one of the distribution transformers fails.

NS ring configuration

This configuration can be viewed as an extension of the configuration with two coupled switchgear. Typically 4 transformers are connected to the same HV line and feed a ring line via a busbar trunking system. In this case, each consumer is supplied by a group of transformers. This configuration is well suited for large systems with a high load density (in kVA / m2). If all consumers can be supplied by 3 distribution transformers, there is full redundancy in the event of failure of one transformer, since the supply of the consumers is ensured at every point of the busbar trunking system. If this is not the case, operation with reduced power should be considered (with partial load shedding). This configuration requires special planning of the protection scheme to ensure full selectivity under all fault conditions.

Fig. D22NS ring configuration

Double-sided NS feed

This configuration is used when maximum availability is required. The basic principle is based on 2 independent energy supply sources. Example:

  • 2 transformers with supply from various HV systems,
  • 1 transformer and 1 generator,
  • 1 transformer and 1 UPS.

An automatic transfer switch prevents the sources from being connected in parallel. With this configuration, preventive and corrective maintenance work on all outgoing electrical distribution devices is possible without interrupting the power supply.

Fig. D23Double-sided LV feed with automatic switchover

Combined configuration

A system can consist of several, differently configured sections, depending on the required availability of the various consumer types. Example: generator and UPS, supply of individual sections via cables or busbar trunking.

1: Simple supply, 2: Coupled switchgear, 3: Double-sided NS feed

Fig. D24Example of a combined configuration

The most likely and most common properties for the various configuration options of the low-voltage supply are summarized in the following table:

Properties to consider configuration
Radial Parallel Load shedding Coupled ring Double sided
Topology of the site any any any 1-5 steps up to 25000m2 1-5 steps up to 25000m2 highly available systems
Choice of location any any any Medium or high Medium or high any
Serviceability minimal default Minimal default default elevated
Power requirement <2500kVA any any ≥ 1250kVA ≥ 2500kVA any
Load sharing Locally concentrated consumers Locally concentrated consumers Locally concentrated consumers Medium or uniform distribution Uniform distribution Locally concentrated consumers
Sensitivity to business interruptions Long break Long break Load shedding Long break Long break Short or no interruption
Sensitivity to electrical interference Low sensitivity High sensitivity Low sensitivity High sensitivity High sensitivity High sensitivity
Other factors / / / /  / Double-sided supply of the load