This paper provides an update to the 2015 paper titled “A New Energy Storage Substation for the Portland to Milwaukie Light Rail (PMLR) Extension” [4] presented at the 2015 JRC in San Jose.

The energy storage substation (ESS) with super-capacitor technology manufactured by Siemens was installed in place of a utility-connected substation at the Tacoma substation location to capture the energy generated by braking light rail vehicles and store it in the ESS energy savings mode and feed it back to the traction power supply during vehicle acceleration. In voltage stabilization mode, the ESS will enable the rail system to maintain voltage system stability by ensuring the system voltage to remain within the required voltage ranges and prevent system disruptions due to low system voltage conditions.

In the Fall 2015, the Tacoma ESS went into service as part of the PMLR Orange Line light rail extension. This paper presents the design concepts for the unit, briefly discusses installation and testing, and focuses on the optimization process, operating experience, energy savings and reliability. TriMet operates a fleet of 145 light rail vehicles on its 60 mile network. Approximately 75% of the energy regenerated during braking is captured and re-used, saving an estimated $1.8 M annually in energy cost. The Tacoma ESS capacity is approximately 2.5 kWh. The unit normally operates in energy savings mode, maximizing recovery and re-use of braking energy while the secondary voltage stabilization mode is available to maintain system operation during outage conditions. After more than two years of revenue service operation, detailed operating data is presented and analyzed, including reliability information and actual energy and cost savings.

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