IEEE Power & Energy Magazine - November/December 2021 - 92

reported in the member states' joint maritime spatial
planning process. By 2050, investments of about €800
billion for large-scale offshore deployment are estimated,
two thirds of which are for offshore infrastructure. European
Network of Transmission System Operators expects
additional needs for massive investments in the onshore
networks together with stepwise growth of sector integration
solutions.
Brazil's vast area, spanning nearly an entire continent,
makes transmission a key flexibility enabler to take advantage
of portfolio effects due to the complementarity of the
multiple weather patterns for solar, wind, and hydro production.
While new transmission links have been planned
for flexibility reasons since 2017, the growth of distributed
generation has made defining transmission investment needs
more challenging.
New Operating Constraints
in System Operation
Increased penetrations of distributed PVs impact bulk
power system reliability. New operating constraints, combined
with new planning processes, may be needed to mitigate
these impacts.
In South Australia, increased distributed solar PVs are
eroding the effectiveness of underfrequency load shedding
(UFLS). Some " blocks of load " are now net generators
during high-PV periods, meaning activation of UFLS
would exacerbate, not correct, the frequency disturbance.
In response, new operating limits are imposed during
import conditions that could result in an underfrequency
condition exceeding the capability of the UFLS system.
Scenarios like this can occur during a sudden loss of the
ac interconnection between South Australia and the rest of
Previous Grid Operation
Installed
Capacity
Operating
Capacity
(For Emergency Use)
Potentially
Wind
Thermal
Solar PV
Step 2
Step 1
Additional Capacity
46 GW
Step 3
Wind
Solar PV
Step 1: Probabilistic Evaluation of Each Generator
Step 2: Release the Capacity By Inter-Tripping In Emergency Condition
Step 3: Grid Access Without Grid Enhancement With the Conditions of Curtailment
figure 6. The line capacity allocation in Japan before and after the connect and manage process. Step 1 is
the probabilistic evaluation of each generator. In step 2, the capacity reserved for emergencies is released
by including only the N-1 contingency. In step 3, operational practices are used to ensure the generation
does not exceed limits, including curtailment (Source: Ministry of Economy, Trade, and Industry.)
92
ieee power & energy magazine
november/december 2021
Thermal
the National Electricity Market. Such scenarios are, fortunately,
relatively uncommon, as high-PV-generation periods
often correlate with export from South Australia across the
ac interconnection. The Australian Energy Market Operator
has also established data feeds from the local distribution
network operator to allow the real-time monitoring of available
UFLS load blocks.
An important factor when assessing system operating
limits in South Australia is the loss of distributed PV
capacity following voltage disturbances. New dynamic load
models for system studies, which can model the observed
disconnection behavior of distributed PVs following voltage
disturbances, have been developed.
To help manage minimum-demand events, arrangements
with the South Australian distribution network operator
have been made for the curtailment of larger distributed PV
installations as well as newly installed residential PV systems.
Aggregations of residential-scale battery energy-storage
systems, developed as virtual power plants, helped during
the record minimum-demand period in October 2020.
These virtual power plants were estimated to have increased
regional demand by around 5 MW via orchestrated charging
of the underlying residential battery energy-storage systems.
Increasing Stability Constraints
Inverter-based resources (IBRs) do not contribute to system
inertia, which can lead to transient, small signal, control, and
frequency stability impacts, depending on real-time system
conditions. In ERCOT, the GTC has been adapted as a tool
to dispatch the system within stability limitations in realtime
operations.
ERCOT has seen an increase in stability constraints in
recent years, particularly in western and southern Texas
New Grid Operation
(For Emergency Use)

IEEE Power & Energy Magazine - November/December 2021

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