IEEE Power & Energy Magazine - May/June 2015 - 86

An added value of the IGREENGrid analysis is providing key
performance indicators to compare and objectively evaluate
different proposals.

working on solutions based on network reconfiguration or
islanding as solution to faults, congestion, or blackouts.
Searching for solutions to increase the capacity to integrate renewables in the grid, the German demonstrator has
proposed a system based on equipment able to locally reconfigure the grid to avoid the congestion risks caused by variations of load and local generation. When DG is connected
to the MV line, it is necessary to avoid reclosing operations
while generators are still connected to the grid; in this case
it could happen during a "parallel mode," causing a hazard
for the electric devices involved. In fact, generators feeding
the line after a disconnection of a grid portion could cause
an undesired island, or in case of fault, generators could feed
the fault, making the reclosing operation useless. The actual
strategy to avoid this kind of dangers is to disconnect the generators as soon as possible.
The central control system of the DSO will send, through
a customer device (protection interface), a trip command to
generation interface devices; this will occur when the system
considers the possibility, from a theoretical point of view, of
generation autonomously supplying the created island.
In the future smart grids, the introduction of advanced
monitoring, control, and communication systems will enable
the distribution network to operate in intentional islanding
so as to exploit the potential benefits introduced by the DG
and the other distributed energy resources. However, given
the current situation for most network operators, especially
on the LV networks where these systems are not present,
islanding is an undesirable operation and not permitted for
the safe and secure operation of distribution systems. The
absence of adequate control systems for DG and of a secure

increase the size as a producer and to provide a more predictable, controllable, and stable power. The limits of applicability when reducing the size of plants is not yet determined. The
potential of aggregating different devices (even considering the
limited flexibility due to the rules imposed by the regulatory
framework) is surprisingly high, and a deep analysis of this
aspect is carried out by the European research project FENIX.
Focusing on the resiliency of distribution networks,
FENIX proposes that a single DG technology is not usually
able to perform the ancillary services required for a significant resiliency improvement (such as voltage control, power
balancing, and islanding operation), but a combination of
some of them is really effective. One of FENIX's dedicated
activities has been focused on the coordination of loads and
generation of a distribution network to emulate the same
behavior of a traditional high-voltage (HV) generation plant.
In a scenario of large DRES penetration, the VPP concept applied to residential generation at district level could
be a good solution for local balancing and voltage control,
but this has yet to be tested.

Fault Isolation, Blackouts, Network
Reconfiguration, and Islanding
Faults in distribution grids are habitually the cause of economic penalties for utilities. Protection systems are usually
designed to deal with punctual incidents, but facing permanent fault events requires more intelligent systems. Several
projects are dealing with this issue. Such is the case of the
automatic grid recovery system proposed by the Spanish demo
of GRID4EU, which automatically reconfigures the MV grid
to recover as much market as possible. Other researchers are

(a)

(b)

(c)

figure 4. Field tests of the smart ID in Pesche, Isernia. (Used with permission from ENEL.)
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may/june 2015

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2015