Imagine stepping into a pod-suitcase in hand-and zipping from city to city at 760 miles per hour through tubes. Imagine suppliers using these pods to transport goods to grocery stores much faster than can be delivered by truck.
You-or those goods-are traveling through another dimension, you might think. But this isn't The Twilight Zone.
Instead, this is an emerging form of transportation called hyperloop. Before launching this type of innovative transportation system, however, hyperloop developers, municipalities, and grid operators must first understand how it will affect the electric grid.
A team of researchers from the Pacific Northwest National Laboratory (PNNL) recently performed a "worst-case scenario" evaluation to determine impacts of hyperloop systems to the grid, with the results published in IEEE Transactions on Power Systems. Their study also helped inform a report published in February 2021 by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, which supported the evaluation.
Setting the stage for modeling hyperloop
To conduct their evaluation, the PNNL team modeled four conceptual hyperloop systems ranging from large metropolitan areas to smaller urban locations, spanning from the West Coast to the eastern portion of the nation.
Systems in California, Colorado, and Ohio represented transportation between cities, while a second California system represented intracity transportation-connecting a station near the San Francisco airport with a location near the Golden Gate Bridge.
The locations were assumed to be less than 10 kilometers (6.2 miles) from an electricity transmission substation with voltage of at least 138 kV-standard high voltage used for transmitting large quantities of power. PNNL's analysis focused on power for pod propulsion and braking, maintaining a vacuum in the tubes, pod levitation, and station and pod electric loads. The simulations assumed industry-grade grid tools were in place and used typical peak summertime electricity load scenarios to represent higher stress on the grid.
Freight flicker
"We focused our attention on the worst-case scenario-the heavy hyperloop pods that make up freight transportation at a high acceleration of speeds up to 760 miles per hour, where the grid simulations showed the most severe load profiles," said Ahmad Tbaileh, the PNNL electrical engineer who led the study.
In the intercity study, the team noted that acceleration and braking from freight loads caused flicker or "jolts"-abrupt and noticeable changes in voltage levels from fluctuations in power demands.
These jolts could cause disturbances in the grid-in the most severe case, power interruption. The grid could be prone to flicker in Colorado, the scenario with the largest impact to electric load and the weakest transmission network. The evaluation also found that some substations used in the smaller location-Colorado-exceeded guidance for preventing flicker and would require mitigation equipment, such as that used for energy storage, for the hyperloop system to be integrated in the grid.
In the intracity study the effects were small compared to the intercity studies, mostly due to smaller pod sizes, lower acceleration, and fewer stops and starts.
The team also found that intercity hyperloop systems will likely require connections to substations with voltage levels of 230 kV or higher, versus the standard 138 kV, due to severe voltage "drops" at lower voltage substations.
The simulations also revealed that the western grid covering California and Colorado exhibited more noticeable disturbances from the rapid electrical load changes spurred by a hyperloop system than the eastern grid connection that covers Ohio. This finding indicated that the western grid may have less response capacity to absorb shocks from hyperloop electricity spikes.
"We focused our attention on the worst-case scenario-the heavy hyperloop pods that make up freight transportation at a high acceleration of speeds up to 760 miles per hour, where the grid simulations showed the most severe load profiles." - Ahmad Tbaileh, electrical engineer
Bolstering the grid
"Ultimately, we found that the continuous pulses or jolts in the intercity hyperloop system caused by freight transportation were large enough that they will likely cause disturbances in the grid," said Tbaileh. "These disturbances could result in violating industry planning guidance used by grid operators for power flicker and fluctuations."
Further, the pulses and jolts would impose significant stress on the power plants that accommodate these sharp pulses. Power plant maintenance requirements would most likely need to be increased if the pulses or jolts are not mitigated through energy storage or other buffering technologies to smooth the sharp rise in electric load. These compensation technologies will most likely be imperative under conditions when the electricity transmission network is under high stress conditions.
Along with Tbaileh, team members included PNNL's Marcelo A. Elizondo, Michael Kintner-Meyer, Bharat Vyakaranam, Urmila Agrawal, and Nader Samaan, as well as Michael Dwyer from Energetics. Their study was supported by the Office of Energy Efficiency and Renewable Energy's Vehicle Technologies Office.
