Hydraulic Motor-Driven Generator (HMDG) in Aircraft

Hydraulic Motor-Driven Generator (HMDG)

Hydraulic Motor-Driven Generator (HMDG)

The HMDG is an AC generator and servo-controlled variable displacement motor. The 400 Hz target output frequency is maintained by the HMDG's architecture. The HMDG could offer a backup supply of electricity in the event of an electrical failure.

Fitted in ETOPs Aircraft

When both the left and right main AC buses are not powered, the hydraulic driven generator (HDG) turns on automatically. The left hydraulic system provides power to the hydraulically driven generator.

The hydraulic-driven generator powers the following AC devices:

  • AC transfer buses on the left and right.
  • AC Standby Bus (via the Left AC Transfer Bus).
  • Transfer Bus for Captain's Flight Instruments.

The hydraulically powered generator powers the following DC devices:

  • Bus Battery
  • Standby DC Bus Bar

DC power generated by fully charged main and APU batteries is greater than that generated by the hydraulically operated generator. The MAIN BAT DISCH and APU BAT DISCH lights may turn on when the hydraulic driven generator initially starts up and continue to do so until the battery power reaches the hydraulic driven generator's output level.

Airbus A 320 HMDG

With power output options of 115 VAC 400 Hz or 28 to 270 VDC, Eaton's hydraulic-driven electric generators which is typically installed on A320 aircraft effectively transform fluid power to primary or emergency electrical power. Our electro-hydraulic servo-controlled constant speed HDEG systems offer a variety of working pressures and flow rates in addition to digital electronic controls for voltage and frequency. They are designed for commercial and military applications. Applications can be modified to meet certain system needs.

Airbus A320 Aircraft generally installed with a hydraulic motor with variable displacement that is coupled with an AC electric generator makes up Eaton's Hydraulic Motor-Driven Generator (HMDG). Over a range of output from 0 to 5 KVA, the HMDG operates the emergency generator at a constant speed of 12,000 rpm. The CSM receives its hydraulic power from a pump that is powered by a ram air turbine. The AC generator operates at 400 Hz and is liquid cooled. Hydraulic motor fluid is circulated around the generator to provide liquid cooling. The Eaton’s HMDG weighs 9.7 pounds (21.49 lbs).


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