**1. Introduction**

The direct current (DC) electric distribution system mainly consists of converters and DC links, as suggested by [1]. The DC distribution systems can be classified as high-voltage direct current (HVDC) or low-voltage direct current (LVDC) for which the DC-AC conversion is located near the end users.

Currently, high-voltage direct current systems are widely used for offshore and submarine electric power transport, [2], in order to interconnect non-synchronized AC grids, thus providing efficient and stable transport and control capacity. HVDC also represents the suitable technology for long-distance energy transport and large amounts of power with reduced power losses [3]. Moreover, HVDC systems stand as a key concept for overcoming the existing barriers concerning the energy generation from renewable sources (wind, solar, or hydropower), since these generating units are rarely located near urban areas or domestic energy consumption points.

The selection of a HVDC topology dedicated to the transport of large amounts of electric power over long distances in a specific case is due mostly to the following aspects:

a.Power control: HVDC is necessary from the technical point of view in order to ensure intelligent control.

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*Micro-Grids - Applications, Operation, Control and Protection*

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Algeria. 2015. pp. 1-6

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**References**


Thus, HVDC systems allow the safe and stable interconnection of AC electrical grids operating at different frequency values, [5], which are otherwise incompatible. In addition, HVDC provides instant and accurate power flow control.

As far as it goes, LVDC microgrid concept has gained the scientific community attention in recent years. A direct current distribution microgrid represents a practical solution to efficiency problems of existing AC electrical grid [6]. While various papers have shown that DC microgrids can play an effective role in solving some operational

**Figure 1.**

*Cost versus transmission distance for HVDC and HVAC systems [4].*

**41**

apply to MCBs.

*Assessment of the Main Requirements and Characteristics Related to the Implementation of…*

issues on the main grid, [7, 8], one paper in particular envisages that a DC microgrid can be used for voltage support, by providing the option of injecting reactive power as an ancillary service [8, 9]. Consequently, the most important aspects regard the integration of renewable energy sources and energy storage systems dedicated to individual end users, in order to improve the quality, reliability, and energy efficiency, respectively [10]. Moreover, the increasing number of DC household appliances has brought to the

Thus, the chapter analyzes researches on DC distribution systems as well as their

potential for residential applications. General advantages of LVDC distribution systems are envisaged, highlighting various power supply architectures and topologies. Also, there are presented demonstration facilities in which LVDC distribution

**2. Analysis of existing standards applicable to DC operating power** 

The following standards are used by the European Telecommunications Standards Institute (ETSI) for the coordination of Telekom stations equipment. These normative documents are required to be applied for DC operation:

• *IEC/EN 60947-2:2009 Low-voltage switchgear and control gear—Part 2:* 

This standard applies to automated circuit breakers, of which main contacts are intended to be connected to circuits, the rated voltage of which does not exceed 1000 V AC or 1500 V DC; it also contains additional requirements for integrally

• SR EN 60947-3:2009 *Low-voltage switchgear and control gear—Part 3: Switches,* 

IEC 60947-2 standardizes miniature circuit breakers (MCB) used by the industry. The aforementioned standard creates a frame for power distribution with voltage values of up to 1000 V AC and 1500 V DC for all rated current ranges starting from 0.5 and reaching 6300 A. There are three types of circuit breakers in this class:

An alternative standard for automatic circuit breakers is represented by IEC 60898-1, which refers to the miniature circuit breakers used within the low-voltage AC grids and included in electrical panels from households, shops, or office buildings. **Table 1** synthetizes the major differences between the two standards which

Another difference is to be observed when comparing the trigger curves. If the IEC 60898-1 standard clearly describes the B, C, and D curves as depending on the rated

This standard applies to switches, disconnectors, switch-disconnectors, and fuse-combination units to be used in distribution circuits and motor circuits of which the rated voltage does not exceed 1000 V AC or 1500 V DC. The manufacturer will specify the type, ratings, and characteristics according to the relevant

*disconnectors, witch-disconnectors and fuse-combination units*

attention both AC and DC distribution systems, as represented in **Figure 2**.

*DOI: http://dx.doi.org/10.5772/intechopen.84413*

systems have been implemented.

**supplies**

*Circuit-breakers*

fused circuit breakers [11].

standard of any incorporated fuses [11].

• Air circuit breakers (ACBs)

• Molded case circuit breakers (MCCBs)

• Miniature circuit breakers (MCBs)

**Figure 2.** *The key diagram for a mixed microgrid with separate AC and DC rings.*

*Assessment of the Main Requirements and Characteristics Related to the Implementation of… DOI: http://dx.doi.org/10.5772/intechopen.84413*

issues on the main grid, [7, 8], one paper in particular envisages that a DC microgrid can be used for voltage support, by providing the option of injecting reactive power as an ancillary service [8, 9]. Consequently, the most important aspects regard the integration of renewable energy sources and energy storage systems dedicated to individual end users, in order to improve the quality, reliability, and energy efficiency, respectively [10]. Moreover, the increasing number of DC household appliances has brought to the attention both AC and DC distribution systems, as represented in **Figure 2**.

Thus, the chapter analyzes researches on DC distribution systems as well as their potential for residential applications. General advantages of LVDC distribution systems are envisaged, highlighting various power supply architectures and topologies. Also, there are presented demonstration facilities in which LVDC distribution systems have been implemented.
