IEEE Power & Energy Magazine - May/June 2015 - 87

According to the results obtained by the More
Microgrids project, the resiliency benefits of islanding
operation are clear.

coordination among the feeder protection systems makes
islanded operation not a viable option.
A "smart ID" island detection solution is being implemented in the Italian Isernia project (Figure 4). The device
is standalone and does not require connection to a communication network or a control system. It operates by using
sampled measures of voltage and current at the installation
point of the smart ID. An islanding operation can then be
detected by comparing the voltage and current phasors to
predetermined threshold levels. Once an islanding state has
been detected, the smart ID device can then be used to trip a
protection relay and disconnect the DG.
The smart ID must be able to detect an islanding operation of the whole or part of the LV distribution network
also in the cases when the frequency variations are within
the thresholds of the DG frequency relays, that is, when
island frequency is within 49.5-50.5 Hz, and voltage
variations are within 0.9-1.05 per unit. The maximum
tripping time should be always smaller than 10 s, and no
nuisance tripping due to short circuits or supply commutations at the MV level are accepted. It should be easy to be
installed, requiring no expert tuning, or threshold setting
procedure.
In extreme circumstances, such as large blackouts, islanding is proposed as a means to recover electricity service as
soon as possible in part of the grid. Innovative strategies for
defences and restoration are being studied, and islanding and
the synchronization algorithms are key factors. IGREENGrid has studied the most relevant ideas and data presented
by Microgrids, More Microgrids, and other projects.
One of the most important contributions in terms of
resiliency is provided by the technologies tested in More
Microgrids. This project has merged the experience of several demonstration activities located in most of the European countries and has demonstrated a clear performance
improvement in terms of grid voltage control.
According to the results obtained by the More Microgrids
project, the resiliency benefits of islanding operation are clear.
In particular, keeping in mind the importance of voltage regulation in distribution grid, from the data reported by the project, it is possible to notice that the voltage quality tends to be
higher for high "self-supply levels" (the ratio between locally
produced and consumed energy). The results have been processed to obtain the IGREENGrid KPIs, and the performance
indicator related to voltage quality results is 0.05 for a 10%
of self-supply level (mostly a passive network). For a level
may/june 2015

of 90% of self-supply (almost a self-sufficient network), the
KPI obtained is 0.25. From the extrapolation of these data,
it is evident that the islanding operation may be beneficial
for the network resiliency, and for a 100% of self-supply
level (for which results are not currently available from More
Microgrids), higher KPI values are expected.
However, the actual resiliency, guaranteed by the functions tested in More Microgrids, strongly depends on two
factors: the optimal allocation of DG along the lines and
the degree of coordination among different players [4]. In
fact, it has been demonstrated that the performance of the
investigated concept of microgrids is largely related to the
effective planning of DG dimensioning and interconnection decisions. An unguided penetration of DG may lead to
more technical problems and to reduce the resiliency of the
distribution network.

figure 5. The advanced supervision system at Corredor
del Henares, Spain. (Used with permission from
IBERDROLA.)
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