IEEE Electrification - December 2021 - 15

analysis (which examines the dynamic response of a system
to critical events), and short circuit analysis (which
ensures that the fault-arresting capacity of substation
equipment, such as protective breakers, is not exceeded).
Modeling inverter-based resources has imposed new challenges
to transmission planners and increased the scope
and complexity of these studies. This is especially true for
BESS and hybrid plants, due to more permutations of possible
operating conditions. Planners need to study different
system load conditions (peak, off-peak, and shoulder
peak) with different BESS dispatch assumptions, such as
discharging and charging. A BESS can go through the full
cycle of maximum charge to maximum discharge during
the peak load hour. Therefore, examining maximum
charging under peak load conditions may be necessary.
Perhaps more importantly, dispatch assumptions for
all resources should be consistent with load conditions.
For example, when a battery is charging under peak load,
solar resources are near their maximum output. Therefore,
battery charging is less likely to cause transmission
system overloads for hybrid and BESS plants next to solar
ones. The growing number of study scenarios has put
many planning entities under pressure and adds to the
schedule and cost risk of interconnection projects.
Some interconnections pose technical challenges that
cannot be evaluated using standard power flow and
dynamic tools. Increasingly, BESSs and other inverterbased
resources connected to weak network areas and in
particularly complex regions may be subject to additional
studies employing more detailed tools, termed electromagnetic
transient (EMT) tools. These require additional time
and expertise from planning teams, and extra studies can
further complicate and delay interconnection processes.
Further complications arise from the magnitude of the
data needed to transpose a model into EMT tools. However,
with a validated and benchmarked EMT model, a
developer can directly match parameters from the model
to the field, a significant benefit during the interconnection
process.
The difficulty of obtaining good models for inverterbased
plants, including BESSs, is present during all stages
of the interconnection process. This is especially troublesome
during early phases of the interconnection process
when various design decisions are still " in flight " and may
change. ERCOT has developed modeling and model validation
requirements pertaining to each stage of the interconnection
process, starting after the initial screening
study and extending to the commissioning stage. Models
must be validated by a project developer through a number
of tests, demonstrating comparable performance in
several simulation tools and corroborated by manufacturer
test results. The modeling and model validation
requirements continuously apply, even after commissioning,
to make sure models are being updated with the latest
changes, such as hardware upgrades and control
setting alterations.
IEEE Electrification Magazine / DECEMBER 2021
15
Interconnection Customer Decision
Deliverability Status,
Deliverability Option,
Megawatts, and so on
TPD Allocation
Choices
IR Processing Phase 1 Study
April~June
Year 1
July~January
Year 1
First
IFS Posting
April
Year 2
Phase 2 Study TPD Allocation
May~November
Year 2
January~March
Year 3
Study Process
Figure 8. The California ISO generation interconnection procedures. TPD: transmission plan deliverability; IR: initial request; IFS: interconnection financial security. (Source: CAISO; used with permission.)
Second
Annual
IFS Posting
May
Year 3
Reassessment
March~July
Year 3 and on
Initial Synch
Commercial
Operation

IEEE Electrification - December 2021

Table of Contents for the Digital Edition of IEEE Electrification - December 2021