IEEE Power & Energy Magazine - September/October 2021 - 20

-10
forecast range. The dotted red line is the inertia expected to be
available as a by-product of the minimum synchronous units
required to be online to maintain system strength.
As the system inertia de creases, the change in grid fre-20
Western
Australia
Northern Territory
-30
Queensland
South Australia
New South Wales
O'ahu
-40
Denmark
-50
Texas
Ireland and
Northern
Ireland
Victoria
Tasmania
Great Britain
115 120 125 130 135 140 145 150
Legend
> 500 kV
300-500 kV
275-300 kV
200-275 kV
NEM
SWIS
quency accelerates for contingencies. Limiting the size of
the largest contingency is an effective way of operating at lower
inertia levels. But the the largest generation contingencies
in the NEM can be set by renewable generation and future
renewable generators could be even larger, which may limit
the effectiveness of such a move.
Fast frequency response reserve helps arrest a faster frequency
decline and is being considered by the Australian Energy
Market Commission, the NEM rule-making body. The fastest
reserve currently procured in the NEM to arrest frequency
is evaluated across a 6-s time frame. The top curved line in
Figure 4 shows the amount of reserve required to meet the
required frequency performance for different system inertia
levels with only a standard response over 6 s. This shows
that, as the inertia level reduces, the 6-s reserve requirement
increases significantly. The other curves show how increasing
the volume of a fast-acting reserve reduces the total amount
of reserve required to meet the required frequency performance,
where the minimum amount of reserve procured is
the static requirement or the size of the largest contingency.
Introducing a mechanism to reduce the size of the largest
figure 1. A comparison of Australia's NEM with other
power systems with a high share of wind and solar energy.
(Source: AEMO; used with permission.)
15
20
25
30
35
40
0255075
2019 (Actuals)
2025 (ISP Central)
2025 (ISP Step Change)
Solar and Wind Penetration (% of Underlying Demand)
figure 2. The instantaneous penetration of wind and solar generation, actual in
2019 and forecast for 2025, under the ISP Central and Step Change generation
builds. (Source: AEMO; used with permission.)
20
ieee power & energy magazine
contingency and increasing the amount of enabled fast frequency
response can allow the system to operate at lower
inertia levels. But no large power system currently operates
without synchronous inertia, and a minimum level of inertia
is expected to be needed in the NEM for the foreseeable
future. To move to system operation
with lower levels of inertia, a
staged approach will be needed to
allow the system frequency control
design to be adapted to the
changing system with capacity
built in advance of the requirement
becoming evident on the system.
A promising development is
synthetic inertia provided by gridforming
inverters. Some of the
largest trials in the world (30 MW)
are happening in Australia. These
trials are demonstrating that in -
verters can provide synthetic inertia
to the grid. While grid-forming
inverters are promising, they are
still in the early deployment phase.
Further experience and analysis
are needed to prove if we can re -
place large synchronous generators'
inertia and safely enable multiple
grid-forming inver ters to
work with the rest of the system
under all conditions.
100
september/october 2021
Underlying Demand (GW)
IEEE Power & Energy Magazine - September/October 2021

Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - September/October 2021
