Noncontacting slip rings capable of kW-level power

The initial prototype for the non-contacting power transfer device promises maintenance free service.

Slip rings on generators are expensive and sophisticated high power devices that wear out at least once in a turbine’s expected 20-year life. Recent rethinking of the device makes use of the capacitive-coupling phenomena to transfer power between non-contacting disc pairs that tolerate vibration – a constant companion in turbine nacelles. “Each channel is a rotary capacitor with one spinning plate and one stationary,” says C-Motive Technologies Inc. (www.c-motive.com) CEO Justin Reed. “The design is a mechanical solution to an electrical problem.”

The company’s capacitive-power coupler is capable of 1W to multiple kW or more per channel across an air gap. Digital signals are also possible. The semi-flexible parallel plates, spaced 0.003 to 0.004 in. apart, tolerate vibration and misalignments. This noncontact approach is said to require no maintenance, and it’s more compact and lighter than inductive power transfer techniques.

“There is no real limit to the number of plates. We’ve also considered segmenting plates into multiple sections for more channels,” suggests Reed.

One power channel requires one spinning and one stationary plate. The air cushion between the plates keeps them from contacting despite vibration.

One of the first prototypes used rigid plates, but the design team could not position them close enough because of mechanical tolerances. “There is always a little wobble and misalignment. Our inventing devised a way to achieve levels of capacitance no one has done before,” he says.

The plates, now flexible, sport an aerodynamic fluid bearing between them. “Because they flex, they float on a cushion of air making them quite durable. You can shake the assembly while running and the plates do not touch,” adds Reed. He says two versions are in beta test now for different industrial applications. WPE