Many of us are familiar with hybrid and all-electric automobiles that return electrical energy to their batteries when braking. But what about rail vehicles? Rail vehicle regenerative braking — returning electrical energy to the rail power distribution system or even back to the supplying utility — offers tremendous opportunities for electrified rail networks to “go green.”
How can system and vehicle characteristics be optimized to maximize the electrical energy being returned to the system through braking? Unlike the closed systems in an automobile, maximizing the environmental benefits of rail networks with regenerative braking requires careful analysis of equipment settings (both on the vehicles and on the wayside electrical equipment), driver behavior, and operating schedules. LTK Engineering Services’ TrainOps rail system simulation software allows rail systems to “tune” their regenerative braking to maximize environmental benefit. By making a rail system more receptive to regenerated energy, operators can lower utility costs, reduce emissions from the supplying utility, and operate their rail vehicles more efficiently.
What about a mix of regenerative braking-equipped and non-equipped trains? Rail systems often debate whether to concentrate all of their regenerative braking-equipped vehicles on one line or to distribute the equipped and non-equipped trains throughout their network. The TrainOps software can quickly compare these two scenarios virtually, identifying which one saves the most. The software's sophisticated algorithms support the optimization process to reduce the carbon footprint of electrified rail networks and optimize their energy saving and energy recovery characteristics.
Rail system electrical engineers know that by increasing the maximum system voltage, they can improve the receptivity of the system to accept regenerated energy. But decisions like this are never easy and require a complex trade-off analysis. In this case, higher voltages on the system may put some electrical components at risk of a reduced life. TrainOps can be used to determine the network energy savings from using higher voltage; the value of this energy savings can then be traded off with the cost of upgrading those electrical components to handle higher design voltages.
Rail systems’ electrical tariffs typically include both consumption and peak demand components. As the utilities’ cost of peak generation capacity increases, the tariffs increasingly weight peak demand in the overall electric bills paid by transit and rail networks. Maximizing regenerative braking offers the opportunity to “shave the peak” so that savings from reduced peak demand can be much greater than reduced consumption. Some utilities measure the peaks at individual supply points while others use the concept of “coincident demand,” looking at all of the rail network’s supply points at the same time.
Even where regenerative braking is used, rail networks may be overtaxing their traction power systems. Unique in the industry, TrainOps also has the ability to trade-off quality of service to rail passengers with controlling demands on the traction power system. For example, a large heavy rail system in the U.S. recently wanted to understand the reduced traction power system stress achieved by imposing downtown speed limits and/or throttle limits for its operators. “We were able to show the benefits in terms of reduced traction power system stress and the fact that travel times for the public would be minimally effected,” explained LTK’s VP for rail operations planning and simulation Bill Lipfert. “More importantly, TrainOps was able to quickly demonstrate the synergistic benefit of both the speed cap and throttle limit instead of invoking one or the other,” he explained. This temporary operating condition will be nearly imperceptible to the system’s passengers while State of Good Repair backlogs are addressed.
TrainOps was specifically developed to enable comprehensive modeling and studies of AC and DC-electrified railroad and transit train operation, as well as operations of fossil fuel-powered trains. The program provides user-friendly inputs (including the ability to “cut and paste” from spreadsheets and other external data sources) for all relevant system and rolling characteristics. These include route alignment data such as track gradients, horizontal alignment and speed restrictions (which can differ by train class) and passenger station locations.
TrainOps also has extensive vehicle libraries with attributes such as weight, dimensions, propulsion system characteristics, and braking system parameters. As an optional overlay, users can include system train control data, including wayside signaling, cab signaling and positive train control inputs, where applicable, with user-friendly “point and click” signal control line data entry. As an additional optional overlay, the electrical power supply system data can be included, comprising traction power supply substations and tie stations (circuit breaker houses) as well as the rail system’s electrical distribution network, such as overhead catenary, trolley wire system, or third rail system, and substation feeder cables. Finally, the software includes flexible input of operations data — either in the form of headway-based input or train schedules — including train make-up, train manipulations at terminals/yards, operating plan inputs, passenger station stopping pattern, train loadings, and station dwell times.
Natalie E. Cornell is Director, Business Development for LTK Engineering Services (www.ltk.com).