Have Questions About Ground Power Solutions? Our Experts Have Answers

An aircraft ground power unit, or GPU, is external ground support equipment that supplies electrical power to an aircraft while it is parked on the ground. A GPU allows maintenance crews and ground support teams to power avionics, lighting, controls, cabin systems, and other aircraft electrical loads without running the aircraft engines or auxiliary power unit.

An auxiliary power unit is installed on the aircraft and uses onboard fuel to provide power when the main engines are off. A ground power unit is an external electrical power source connected to the aircraft while it is on the ground. A GPU is preferred during extended ground operations because it avoids unnecessary APU runtime, costly fuel consumption, and increased maintenance wear.

Ground power units reduce fuel burn, engine wear, noise, and emissions during ground operations. Instead of operating the aircraft’s main engines or auxiliary power unit while the aircraft is parked, crews can connect the aircraft to an external electrical GPU for maintenance, preflight checks, software updates, avionics testing, and other powered ground operations.

Aircraft use 400 Hz electrical power because higher-frequency AC power allows motors, transformers, and other electrical components to be smaller and lighter than equivalent 50 Hz or 60 Hz equipment. Weight reduction is critical in aviation for many reasons, which is why 400 Hz power is widely used for aircraft systems and aircraft ground power support.

A solid-state frequency converter electronically converts available input power into the voltage and frequency required by the aircraft. For aircraft ground power, this often means converting facility power into 115/200 VAC, 400 Hz aircraft power. Solid-state designs reduce the mechanical wear, maintenance, and output instability associated with older motor-generator frequency converters.

A solid-state frequency converter rectifies incoming AC power into DC and then uses power electronics to invert that DC into a controlled AC output at the required voltage and frequency. This allows the converter to provide stable 400 Hz aircraft power when the incoming utility frequency is 50 Hz or 60 Hz.

Aircraft commonly require 400 Hz AC, 28 VDC, or 270 VDC external power, depending on the aircraft platform and onboard electrical architecture. Many commercial, business, military, and special-mission aircraft use 115/200 VAC, 400 Hz power. Many helicopters, turboprops, business aircraft, and military aircraft use 28 VDC. Advanced military and more-electric aircraft may require 270 VDC for ground maintenance and system testing.

Unitron supports military aircraft ground power applications requiring 400 Hz AC, 28 VDC, 270 VDC, or a combination AC/DC power. These applications can include flight line support, maintenance hangars, depot maintenance, avionics testing, aircraft system checks, and advanced military aircraft electrical system support.

Unitron ground power systems can support UAV, autonomous aircraft, and advanced aircraft programs when the aircraft or ground test environment requires 400 Hz AC, 28 VDC, 270 VDC, or combination power. Specific requirements should be reviewed by aircraft platform, ground test procedure, connector type, duty cycle, and facility input power.

270 VDC is important because advanced and more-electric aircraft architectures increasingly use higher-voltage DC power to support electrical loads, reduce current levels, and improve power distribution efficiency. Ground support equipment must match the aircraft electrical architecture so maintainers can safely power and test these systems while the aircraft is on the ground.

Yes. Unitron frequency converters and programmable power supplies can be used in aircraft production, research, laboratory, and test environments where controlled AC or DC power is required. These applications may include aircraft component testing, avionics support, electrical system development, and production-line validation.

MRO (Maintenance, Repair and Overhaul) facilities use aircraft frequency converters to power aircraft during inspections, troubleshooting, avionics testing, software updates, lighting checks, cabin system checks, and other maintenance activities. External ground power allows technicians to work without running the aircraft engines or relying on onboard batteries.

The Unitron PS Series is a programmable frequency converter series designed to operate from a wide input frequency range and provide selectable 50 Hz, 60 Hz, or 400 Hz output power depending on the configuration. The PS Series is used onboard in aircraft and vehicles, as well as research laboratories, and other specialized power applications.

To choose the correct aircraft GPU, confirm the aircraft’s required output type, output load requirement, connector, frequency, input and output cable lengths as applicable, input power, installation location, and environmental conditions. The most important starting point is whether the aircraft requires 400 Hz AC, 28 VDC, 270 VDC, or a combination output.

When requesting a GPU quote, provide the aircraft type, required output voltage and frequency, required kVA or kW, input voltage available at the facility, required input and output cable lengths needed, connector type, indoor or outdoor use, mobile or fixed installation preference, and any applicable military, facility, or safety specifications.

Voltage is the electrical potential supplied to the aircraft. Current, measured in amps, is the amount of electrical flow. Frequency, measured in hertz, applies to AC power and describes how many cycles per second the current alternates. kVA is apparent power for AC systems, while kW is real power and is commonly used for DC systems such as 270 VDC aircraft power supplies.

Cable length matters because longer cables create voltage drop and can affect power quality at the aircraft connector. The correct cable size and length should be selected based on output current, aircraft requirements, voltage regulation, connector type, and how the unit will be positioned relative to the aircraft.

Important aircraft GPU safety features include voltage and current monitoring, overvoltage protection, undervoltage protection, input monitoring, current limiting, emergency power-off, fault indication, and appropriate enclosure ratings for the operating environment. For hangar use, the installation should also consider applicable hazardous-area safety clearance and facility electrical requirements.

GPU cables and connectors should be inspected regularly and before use, especially in demanding operating environments. Look for worn insulation, damaged plug heads, loose contacts, overheating, corrosion, exposed conductors, bent pins, and signs of improper handling. Damaged cables or connectors should be removed from service and repaired or replaced before connecting to an aircraft.

Solid-state aircraft GPUs generally require routine inspection of cables, connectors, terminals, fans or filters, displays, meters, and enclosure condition. Operators should also verify output voltage, frequency, current monitoring, fault indicators, and any communications or diagnostic functions according to the manufacturer’s maintenance schedule.  Contact Unitron if you would like us to set you up with a preventive maintenance plan.

Yes. Unitron can review aircraft, hangar, MRO, flight line, military, and test-lab power requirements and recommend an appropriate ground power configuration for your specific needs. Requirements may include output type, power rating, input voltage, environmental conditions, cable length, installation type, controls, communications, diagnostics, and applicable specifications.

One Unitron GPU can support multiple aircraft types if the aircraft share compatible electrical requirements, connector types, output ratings, and operating procedures. Mixed fleets often prefer multiple output types, which is why 400 Hz/28 VDC and 400 Hz/270 VDC combination GPUs can be useful.