IEEE PES T&D Conference & Exposition 2022 - 77

SSSCs inject a leading or lagging voltage in quadrature
(shifted 90 degrees) with the line current, providing
an FSC or series reactor's functionality, respectively.
However, due to the active nature of SSSCs, the compensation
solutions do not have the negative characteristics
of passive devices and legacy compensation installations,
such as the risk of stimulating SSOs and the constant reactive
power consumption.
Through voltage injection utilizing voltage sourced
converters, SSSCs effectively increase or decrease the
reactance of a given circuit, enabling real-time control of
power flow. This solution is most effective in meshed electric
grids to resolve loading violations by utilizing spare
system capacity.
SSSC solutions operate in series with the transmission
owner network facility. Unlike traditional SSSC solutions,
M-SSSCs operate at line potential with no connection to
ground and do not need an insertion/coupling transformer.
The inherent modular nature of M-SSSC deployments
enables utilities to design deployments to meet the
immediate, more certain system need. If the system need
grows in the future, the deployment will easily scale by
adding more modules. Along with scaling the existing
deployment, the M-SSSC devices are voltage-agnostic
and can be easily redeployed to other lines with different
voltage levels.
Given the fast response of the M-SSSC power electronics,
operators can frequently change the M-SSSC operating
setting. This enables the active management of power flows
with no degradation in device life. M-SSSCs can operate
under several control modes. Operators can set the M-SSSC
controls to maintain a fixed reactance by varying the injected
voltage as a function of line current to maintain a fixed voltage
injection or maintain the line current.
Traditional flexible alternating current transmission systems,
like SSSC or FSC, require extensive civil works for
installation, a large footprint, and a custom design for the
specifications of a particular application and deployment
site. The modular design of the M-SSSC facilitates rapid and
cost-effective deployment and redeployment with significantly
less customized design work, allowing the solution
size to be scaled up or down to support the dynamic needs of
the transmission grid. M-SSSC devices are currently available
in modules of 1 MVAr up to 10 MVAr. These are typically
installed as a fleet, connected across all three phases,
and enable a continuous range of control up to the collective
rating of the deployment. Utilities typically deploy M-SSSC
devices in or adjacent to a substation or as part of a mobile
unit for rapid deployment.
Subsection 2.2: Switch from FSC to M-SSSC
Central Hudson and Smart Wires, a technology supplier,
sized the M-SSSC deployment to meet the 3.5 Ohm (21%
series compensation) need on the Leeds-Hurley Avenue
line under the summer short-term emergency (STE) rating.
April 2022 Show Issue
Since its voltage injection is inversely proportional to the
line current, M-SSSC technology can deliver far greater
compensation in normal operating conditions when currents
are lower than the STE. Table 1 shows a summary of
the M-SSSC solution.
The requirement of at least 3.5 Ohm of capacitive reactance
at the STE rating is equivalent to 11.72 kV of capacitive
voltage injection. A voltage injection capability of 2,830 V
per device resulted in five M-SSSC devices per phase (15
total), resulting in 14.15 kV of voltage injection capability.
The effective impedance change achieved by this M-SSSC
deployment is inversely proportional to line current and, for
example, can provide +/- 7.07 Ohms at 2000 A. This reactance
can be capacitive or inductive, hence the positive
or negative.
Shifting the Hurley Avenue series compensation to an
M-SSSC solution yielded a similar total project cost to the
FSC option. It also resulted in numerous system impact,
design, and installation advantages.
From a system impact perspective, the M-SSSC solution
had significantly less impact on protection schemes. Since
M-SSSC devices inject voltage instead of connecting capacitance,
there also is a negligible risk of causing SSR. From
a design and installation perspective, the modular nature
of M-SSSC devices enables a more creative and efficient
deployment footprint compared with the large-bulk FSC.
The FSC solution required over 25% more substation space
than a ground-mounted M-SSSC. Flexibility in deployment
design and efficient use of substation space further tipped
the scales for Central Hudson to proceed with the M-SSSC
solution. As a final improvement on the risk profile of the
deployment, multiple M-SSSC devices inherently present no
single point of failure.
One of the significant cost-saving features of the M-SSSC
solution stems from the fact that the protection circuitry of
the M-SSSC solution allows Central Hudson to avoid significant
relay upgrades required with the FSC option. Central
Hudson and Smart Wires worked with Schweitzer Engineering
Laboratories (SEL) to perform a relaying study and tests.
The scope of testing included studying the performance of
the relays protecting the 345 kV Leeds-Hurley line by building
a reduced power-system model of the line and adjacent
lines using RSCAD.
SEL performed a suite of tests on these lines under various
loading conditions to study the performance of the protective
elements with no compensation and with M-SSSC
device compensation in capacitive and inductive modes.
table 1. Summary of Leeds-Hurley M-SSSC Solution.
Series Compensation Required
3.5 Ω
Voltage Injection per Phase Required 11.72 kV
Voltage Injection per M-SSSC Device 2,830 V
M-SSSC Devices per Phase
5
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