**Author details**

• Increased economic efficiency: the unpredictable blackouts of electrical grids are removed, the maintenance time and costs are reduced, the weak points of the installations are quickly

• Increased operation safety: accidental interruptions of electrical grids are not possible due to insulation faults, the exact location of the insulation faults can be established, the electrical installations are maintained at a high operation level, and the circuits are being moni-

• Optimal maintenance: The insulation faults are found and quickly indicated, automatic location of a system section (subcircuits) with isolation faults is possible, optimal personnel and repairing time planning, complete and centralized information regarding the electrical

• Enhanced protection against fire: the insulation faults are found in incipient phase. Thus, there are no major isolation faults, the isolation faults representing the main fire starters. The use of insulation transformers as well as monitoring and remote diagnosis via Internet/ Ethernet allows the separation of certain sections (electrical subgrids) that can be exposed

• Enhanced protection against accidents: the removal of electroshocks by disconnecting the faulted systems or circuits and the prevention of disturbances in the control circuits of vari-

This chapter proposes some solutions about the topics of unconventional backup structures used in smart microgrids. The issue is of interest particularly in connection with the problem of ensuring continuity in power supply. In this context, firstly the case of the switching to the backup power supply, in the case of a low-voltage symmetrical grid when using two frequency converters, one of which is alternately maintained in cold reserve, is presented. The only consumer is an asynchronous motor with a short-circuit rotor with nominal active power P = 22 kW. The logic of switching and electrifications is ensured by using an associated software of a microprogrammable automaton. Secondly, the switching to the backup power supply, in the case of low-voltage symmetrical smart microgrids using an electric generator set or using an electric generator set and the photovoltaic panels, in the case of modern residential buildings, is proposed. The microgrid is symmetrical and uses two identically transformers, T1 and T2, one of the transformers being alternately in hot reserve state. The users are divided into two categories: critical and noncritical ones. Finally, the implementation of recloser devices for autoconfiguration and automatic connecting/disconnecting decisions, in order to switch on the backup power supply, is presented. It is expected in the future realized the conversion of the public grids to active (distribution/using) grids that use high-tech smart devices like reclosers. The grouping together of these smart microgrids that have the auto-reconfiguration option through implementation of the recloser type devices is also considered in the development of smart grids. In this context the implementation of the recloser-type devices for switching on the backup power supply, for the

case of a two radial structures of a public grid with isolated neutral, is presented.

installation state, monitoring and remote diagnosis via the Internet/Ethernet.

observed, and better organization of investment is possible.

tored both online (under load) and offline (off).

to fire from the rest of the power system.

ous equipment and electric machines.

**6. Conclusions**

96 Smart Microgrids

Lucian Pîslaru-Dănescu<sup>1</sup> \* and Laurențiu Constantin Lipan2

\*Address all correspondence to: lucian.pislaru@icpe-ca.ro

1 National Institute for Research and Development in Electrical Engineering ICPE-CA, Bucharest, Romania

2 University Politehnica of Bucharest, Bucharest, Romania
