Farnborough Air Show

Eldec does electronic balancing act

 - November 15, 2006, 6:22 AM

The Eldec division of Crane Aerospace & Electronics (Hall 4 Stand G20) is showing an example of what it reckons is the ideal means of reconciling a growing demand for more powerful on-board electrical equipment with new restrictions on the effect individual loads can have on the aircraft power supply.

According to Mark Stefanich, director of aircraft electrical power solutions, power quality is an industry-wide issue. New-generation aircraft such as the Airbus A400M and Boeing 787 are demanding more power for tasks that previously relied on hydraulic and pneumatic systems at the same time as they dispense with constant frequency generators.

That means the variable-frequency three-phase alternating current has to be converted to the direct current used by most aircraft equipment. But the conversion process can cause distortion of the current on the electrical bus, so RTCA DO-160, the document that governs environmental conditions and test procedures for airborne equipment, has been revised to take into account the changes.

Chief engineer Kaz Furmanczyk said the most significant requirement in the revised document is the restriction on individual harmonics generated by user equipment rated 35 VA or more. The result is that almost all motor drivers using direct rectification need to be replaced or upgraded, and most transformer rectifier units need to use higher than the traditional six-pulse or active switching techniques to meet the new power quality limits.

Eldec has a long background in aircraft electrical systems and Stefanich said research and development aimed at meeting the new power quality requirement started around five years ago. “We looked at options, active and passive, and various forms of each,” he said. “Now I think we have an optimal solution.”

The company’s solution has taken the form of an auto transformer rectifier unit that offers up to 98 percent efficiency, a range of cooling options and 18- or 30-pulse multiphase conversion to meet the new standard.