IEEE PES T&D Conference & Exposition 2022 - 76

these transmission corridors allowing increased integration
of renewables.
Central Hudson has led the way in utilizing a high-impact
GET, the modular static synchronous series compensator
(M-SSSC). The M-SSSC solution will ensure the full deliverability
of several renewable generation projects within the
next few years. In addition, its efforts to evaluate the technology
in a pilot project, in advance of deploying it to solve grid
challenges, enabled it to gain experience with the solutions
and contribute to advancements in the technology that has
already benefited grids globally.
Section 1: Series Compensation Project
In New York State, generation developers proposing interconnection
projects submit an interconnection request to
the NYISO. Once the request is received, the NYISO and
the impacted transmission owner cooperatively conduct
the final study of the NYISO interconnection process. This
study is known as the Class Year Facilities Study. It involves
studying the impact of all class year generators on the system
as a whole. For capacity resources, this study includes
a system deliverability study. NYISO will propose a System
Deliverability Upgrade (SDU) project if capacity resources
are required to maintain system reliability due to the proposed
interconnections.
The system deliverability studies, as part of class years
2009, 2010, and 2011, found that the Upstate New York/
Southeast New York (UPNY-SENY) interface transfer
capability is constrained. The transfer capability of the
UPNY-SENY interface needs to be improved by 185 MW
to ensure the deliverability of class year projects. To accomplish
this, the NYISO proposed 21% series compensation
on the 345 kV Leeds-Hurley Avenue line. This level of
compensation typically requires relay upgrades to address
reliability and security concerns associated with distance
protection relays.
The NYISO's original proposal for series compensation
used a fixed series capacitor (FSC) located at Central Hudson's
Hurley Avenue 345 kV Substation. A preliminary protection
study identified impacts to area protection schemes
that Central Hudson would need to address. Voltage and
current reversal concerns would result in a significant and
costly relaying upgrade project. Sub-synchronous resonance
(SSR) interactions, which result from mechanical/electrical
interactions among the components of a turbine-generator's
shaft and the electrical system, also raised concerns. A
screening study commissioned by the NYISO identified the
potential for SSR interactions with the Roseton and Athens
generating units. A more detailed analysis would be needed
to determine the impacts and proposed mitigation. The relay
upgrades and SSR mitigation would add significant costs to
the project.
While widely used, FSC installations have documented
challenges with implementation and operation. The most
common issue is the potential for the FSC to resonate at
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ieee power & energy magazine
sub-synchronous frequencies, known as sub-synchronous
oscillations (SSO). The two most common types of SSO
are sub-synchronous torsional interaction (SSTI) and subsynchronous
control interaction. Torsional interaction is the
opposing torque forces between the turbine-generator shaft
and the electrical grid. Control interactions occur when
doubly-fed induction generator controls act to " amplify "
sub-synchronous currents entering an induction generator,
such as wind turbines. This results in high torsional stress
on generator rotor shafts and instability in power electronic
control systems.
Regions across the globe have observed the SSR phenomenon.
One event that occurred in 2016 in Latin America
resulted in extensive damage to generation facilities due to
SSR interactions, and more specifically SSTI, between the
generation facilities and the FSC. Four gas-fired generation
units in Latin America in proximity to multiple FSC installations
had to be placed off-line following fractures and
arc-flash damage identified at the shafts. A detailed postmortem
investigation determined the root cause of the event
and developed preventive measures. As a result, multiple
FSC installations in the region are out of service to avoid the
recurrence of SSR incidents.
Mitigations for SSR are often costly and can include
intentionally constraining nearby generation or limiting the
power flow control impact of the series compensation. Given
the many operational and economic implications of mitigation
options, the fastest and most practical solution is to
permanently bypass any FSC installation found to be at risk
of SSR interactions. However, doing so effectively eliminates
the contribution of capacitive reactance to the grid and
strands multimillion-dollar investments. Even when initial
studies do not show SSR issues, changes to the grid topology
and generation in the future could result in conditions for
SSR to occur.
Concerns with impacts on area protection schemes,
SSR interactions, and cost led Central Hudson to evaluate
alternative power flow technologies. It ultimately selected a
M-SSSC for this project. The modular nature of the device
made it ideal for the application at Hurley Avenue as the
NYISO studied the impact of capacitive series compensation
up to 30% on the 345 kV Leeds-Hurley Avenue line. The
installation of additional modular units can quickly address
future compensation needs.
Section 2: Modular SSSC Solution
Subsection 2.1 Modular SSSC Technology
Over the past decade, modular power flow control solutions
have been deployed on electric grids worldwide. These flexible
solutions are built by packaging SSSC components into
standard, modular devices. M-SSSC technology maintains
the functionality and benefits associated with traditional
power flow control technology while minimizing the associated
challenges.
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