Siemens, a German manufacturer of a wide variety of items (you could consider it Germany’s GE), is installing a regenerative braking energy storage system for the new TriMet Portland-Milwaukie Light Rail Transit Line, a first in the US.
It is the Sitras Energy Storage unit and is powered by ultracapacitors (sometimes called supercapacitors or EDLCs). Ultracapacitors are very heavy, but they can provide massive bursts of power very quickly, and that is desirable for acceleration of light rail transit at times.
This system will operate by capturing the kinetic energy possessed by the light rail train while it is braking to help slow it down and also generate electricity, which is then stored by the mentioned energy storage system.
The energy storage system will then power the light rail train when it is accelerating. Powering the train with an energy storage system during acceleration prevents the massive power consumption spike caused acceleration, providing a form of voltage stabilization.
These power consumption spikes cause a phenomenon called “voltage sag,” or a “voltage drop.”
When you draw current from any power source, it causes the voltage to decrease. The extent of that is determined by the amount of current drawn relative to the amount of current it is designed to provide.
Due to the fact that other trains are sometimes connected to the same power sources, they can cause power disruptions if too many of them simultaneously accelerate due to excessive voltage sag, causing the voltage to drop below the required level.
Finally, this regenerative braking system improves energy efficiency. “The regenerative energy storage unit is an important piece of the many sustainable elements being incorporated in this light rail project,” said Dan Blocher, executive director of TriMet Capital Projects. “With Siemens as a partner, we know this pilot project is positioned to bring a new and efficient technology to the U.S.”
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