Development of 200 Ampere Regulated Transformer Rectifier

Modern aircraft are experiencing three trends which are impacted by older TRU characteristics. The first is that airframes are being used for longer periods of time; scheduled use is being increased to avoid the budget constraints of replacing costly airframes. The second, related trend is that these longer-life airframes are being updated/modified with avionics, mission equipment, and/or ordinance which in many cases is microprocessor-based (digital) and therefore DC-powered. When older TRUs and/or existing aircraft electrical systems were originally developed, they did not consider these new loads. In many cases this new equipment is highly sensitive to low voltages and/or DC power quality “noise”. When new equipment is installed on older aircraft, both higher DC loads and nuisance trips/power quality issues in general can be a problem. The US Navy aircraft fleet is experiencing an increasingly common problem of nuisance tripping due to poor voltage quality from older, and overloaded, TRUs. The third trend is related to DC buss growth which results in poor charging of aircraft batteries that “float” on the DC buss.

Smiths Industries Aerospace - Leland Electrosystems has designed and developed a family of Regulated Transformer Rectifier Units (R/TRUs™) which greatly enhance the quality of DC power in aircraft applications. Naval Air Systems Command, Electrical Power Systems Division (EPSD) began a Qualification Test Program on a 200 ampere R/TRU™ in FY 98/99. The objectives of the USN program were to qualify a device which would:

Provide constant DC voltage output over 0-100% load,

Program objectives were to replace four (4) existing TRUs in US Navy inventory with one ( 1 ) common design that would meet both MIL-C-7115 electrical requirements (especially overload current requirements) and the worst case environmental requirements existing aircraft applications.

This paper discusses the approach taken to establish requirements for the R/TRU™, the development approach, R/TRU™ basic design, and qualification test results. The paper also discusses the aircraft that the 200-Ampere R/TRU™ is compatible with, and the status of Navy Flight Evaluation.