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Wireless Electricity Transmission Being Deployed to Power Korean Mass Transit

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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.
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Story Update: Two Inductively-Powered busses are in regular operation

South Korea's OLEV Electric City Bus Recharges via Cables Buried in Road
Shane McGlaun (Blog) - August 7, 2013 9:27 AM

The Korea Advanced Institute of Science and Technology has developed a pair of electric buses called Online Electric Vehicles or OLEV. These buses are different from your typical electric vehicles that have to be parked to recharge the batteries. Instead, they can recharge while driving down the road.

Electricity is sent to the bus via cables buried in the road with an 85% maximum power transfer efficiency rate (the wireless charging technology is able to supply 60 kHz and 180 kW of power at a stable and constant rate). There is a gap of just under seven inches between the underbody of the electric bus and the road surface. The charging system uses Shaped Magnetic Field in Resonance [PDF] to transfer power to the bus while it’s in motion.

The underbody of the bus has a receiving device that is able to convert the magnetic fields into electricity. The power strips needed to power the bus only cover 5 to 15 percent of the road surface, so only small sections of road have to be rebuilt to provide service.

Both of the OLEV buses are currently operating in the city of Gumi, South Korea. As of August 6, the buses are running an intercity route between the Gumi Train Station and In-dong district spanning 15 miles round-trip.

The technology used in the OLEV buses is an offshoot of tech used to power trams at an amusement park in South Korea.

Sources:, KAIST
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