IEEE Power & Energy Magazine - May/June 2017 - 47

1) The first isolation step will be performed between distributed IED controlling circuit breakers, and this IED
will be provided with protection functions.
2) The second isolation step will be performed between
distributed IED controlling switches once the first isolation step is finished; this IED will be provided with
fault passage indicators.
3) The restoration algorithm will be run at the SAU level to
consider DER capacity and alternative branches for mesh
networks, thus obtaining a more efficient restoration.
Both isolation steps integrate a backup chronometric selectivity allowing for the provision of backup operations in case
the logic selectivity fails. In this way, the reliability indexes
are even better. In addition, DER coordination commands are
included to command disconnections of DERs when required
to avoid islanding situations or unnecessary reclosings. Blocking commands to avoid unnecessary disconnections are also
sent from FLISR IEDs to avoid unnecessary disconnections
from the distribution grids.
Congestion Management

distribution network, the hosting capacity provided by the secondary controller is typically three to four times greater than the
hosting capacity of a passive network and two to three times
higher than the hosting capacity of an active network utilizing
only primary controllers.
Figure 4 illustrates the hierarchy of the controllers and
their interactions. Secondary controllers are located at primary or secondary SAUs depending on which network, the
MV or LV grid, they are managing. The tertiary controller is
located in the DMS.
DSO/TSO Information Exchange

Phasor measurement units (PMUs) located in distribution
grids provide valuable information for a TSO to determine
real-time and adaptive reduced models of active distribution
networks for transmission system management. This helps the
TSO determine reduced models more accurately and includes
complexities and interdependences between transmission and
distribution systems. One crucial piece of information, of
immediate interest to the exchange between DSOs and TSOs,
is the equivalence of distribution network models. PMU data
can also be exploited for dynamic line rating at the distribution level, small-signal oscillation detection, and voltage stability assessment.
The work carried out in IDE4L shows that accurate time
synchronization is paramount for the use of PMU data in the
different applications discussed earlier, which use PMUs as input. Hence, one key recommendation from IDE4L is to support

Congestion management is a three-layer control hierarchy.
First, the tertiary controller calculates dynamic grid tariffs
to be introduced for commercial aggregators and retailers to
prevent congestion conditions before day-ahead market closing. Second, the tertiary controller validates flexibility service
actions of commercial aggregators within the DSO's network
and purchases flexibility services if needed to solve congestion. This controller also plans the
optimal network topology for the
next day to prevent congestion. In
addition to the main algorithms,
Day-Ahead
Flexibility
Day Ahead and Intraday
the tertiary controller also contains
Market
Market
a state estimator and a forecaster
to provide states and forecasts as
Tertiary
Commercial
Long-Term
inputs for the other algorithms.
Control
Aggregator
Forecast
The secondary control for distribution grid congestion management
e.g., Network e.g., CRP and
Reconfiguration
SRP Signals
optimizes the settings of primary
controllers to enhance the hosting
Real Time/Intrahour
Short-Term
capacity for DERs and solve ocForecast
casional congestion problems. The
secondary controller, which runs in
Secondary
State
Secondary
Monitoring
real time, is based on optimal power
Control
Estimation
Control
flow to minimize operational costs
e.g., V/VAr
e.g., DER
like losses, production curtailment,
Regulation
Scheduling
and demand response. As an input,
it needs the state estimation of the
IED, Primary
IED, Primary
e.g., Fault Location
control area. The secondary controlControl
Control
ler is of greatest benefit for cases
Hard Real Time
in which congestion occurs occaCB, OLTC
CB, DER
sionally, network reinforcement
costs are high, and the control area
includes several controllable DERs
and network elements. In a weak figure 4. The hierarchy of controllers.
may/june 2017

Market
Tertiary
Controller

Secondary
Controller
Monitoring
Estimation
Forecasting

Primary
Controller
Primary
Device

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2017