Korean trams and buses are moving away from overhead power wires and high-voltage third rails—literally.
Researchers at the Korea Advanced Institute of Science and Technology
(KAIST) have made major advances in wireless power transfer for mass
transit systems. The fruits of their labor, systems called On-line
Electric Vehicles (OLEV), are already being road tested around Korea.
At it’s heart, the technology uses inductive coupling
to wirelessly transmit electricity from power cables embedded in
roadways to pick-up coils installed under the floor of electric
vehicles.
The work was hailed as one of the year’s top 10 emerging technologies by the World Economic Forum this week.
Engineers say the transmitting technology supplies 180 kW of stable,
constant power at 60 kHz to passing vehicles that are equipped with
receivers. The initial OLEV models above received
100 kW of power at 20 kHz through an almost eight-inch air gap. They
have recorded 85 percent transmission efficiency through testing so far.

(A concept drawing for an OLEV tram. Courtesy KAIST.)
The wireless electricity that powers the vehicle’s motors and systems
is also used to charge an on-board battery that supplies energy to the
vehicle when it is away from the power line.
KAIST plans to start deploying the OLEV technology to tramlines in May and high-speed trains in September.
“We have greatly improved the OLEV technology from the early
development stage by increasing its power transmission density by more
than three times,” said Dong-Ho Cho, the director of KAIST’s Center for
Wireless Power Transfer Technology Business Development, in a release.
“The size and weight of the power pickup modules have been reduced as
well. We were able to cut down the production costs for major OLEV
components, the power supply, and the pickup system, and in turn, OLEV
is one step closer to being commercialized.”
The institute announced that buses equipped with the wireless power
transfer technology are already used daily by students on the KAIST
campus in Daejeon, while others are undergoing road tests in Seoul. Two more OLEV buses will begin trial operations in the city of Gumi in July.
Proponents say that the technology banishes overhead power lines and
rails for electric trams and buses, dramatically lowers the costs of
railway wear and tear and allows smaller tunnels to be built for
electric vehicle infrastructure, lowering construction costs.

(An OLEV shuttle bus that provides rides to students and faculty on
the KAIST campus in Daejeon. Courtesy Hyung-Joon Jeon/KAIST.)
Top Image: KAIST and Korea Railroad Research
Institute displayed wireless power transfer technology to the public on
Feb. 13 by testing it on railroad tracks at Osong Station in Korea.
Photo courtesy Hyung-Joon Juen/KAIST.