What is a Ground Power Unit (GPU)?

A Ground Power Unit (GPU) is a mobile or stationary device, sometimes also referred to as Aircraft Ground Power, which is used to provide electrical power to aircraft while they are on the ground. When an aircraft is on the ground, it requires electricity to run various systems, such as lights, avionics, and air conditioning. This power can either come from the on-board auxiliary power unit (APU) or the GPU. The GPU is connected through an cable to the aircraft and provides the necessary electrical power to operate the on-board systems. In general the GPU provides 115 Volt Alternating Current (AC) at 400 Hz only smaller aircraft operate with 28 Volt Direct Current (DC).

The utilization of ground power units (GPUs) allows the auxiliary power unit (APU) to be deactivated. Switching of the APU results in a decrease in airport noise and emissions, in addition to the reduction of fuel consumption and auxiliary power unit wear.

The GPU is not sufficient for starting the aircraft engines. Only twin-engine business aircraft are started with an electric starter. Larger fan engines in today's commercial aircraft require compressed air to start the engines. For this reason, the auxiliary engine of the aircraft must be started shortly before the engine starts in order to supply the compressed air required to start the main engines. The ground power unit then only supplies the power for starting the auxiliary power unit.

The power required by the Aircraft depends on its size. Larger aircraft have 2 or even 4 standardized 90 kVA connectors.

• Narrow-Body Aircraft: 1 x 90 kVA
• Wide-Body Aircraft: 2 x 90 kVA
• A380 Aircraft: 4 x 90 kVA

GPUs can be differentiated in mobile ground power units and stationary ground power units.

Mobile Ground Power Unit

Mobile GPU typically consist of diesel power generator or a large electrical battery and can be either towable trailer mounted or mounted on a truck. Battery powered GPUs are referred to as eGPUs. The use of eGPUs can reduce the noise and CO2 emissions.

Fixed GPU / Fixed Electrical Ground Power (FEGP)

FIxed GPU or Fixed Electrical Ground Power (FEGP) provide power to the aircraft using a permanent installation for use on parked aircraft. In comparison to mobile GPUs fixed GPUs do not need to be recharged or refueled. The conversion of the mains electricity (in Europe 230 V at 50 Hz in US/Canada 110V at 60 Hz) to 115V at 400 Hz power is typically done either centralized or at the point of use by frequency converters.

The image below shows a fixed GPU. Two bridge mounted cable coils are attached to the passenger boarding bridge (PBB) and electrically controlled to dispense the 400 Hz cable. After operations, the device will electrically rewind the cable back onto it's cable reel.

Power Connector

The connection to the aircraft itself is made using standardized power connectors for aircraft. Aircraft connectors are standardized and rated at IP67.

Pre-Conditioned Air System (PCA)

Contemporary airport facilities frequently employ Pre-Conditioned Air Systems (PCAs) in conjunction with GPUs to provide conditioned air to the aircraft via the passenger boarding bridge. The PCA is an advanced air conditioning system designed to transfer conditioned air directly to the aircraft, augmenting the electrical power supply obtained from the GPU.

APU vs GPU: Reduction of Power Consumption, Emissions and Noise

The use of mobile GPU and even better eGPU, FEGP and PCA reduces power consumption, emissions and noise. Hence, it increases efficiency, protects the environment and saves money on fuel.

Emission Reductions per Hour

A study by the Airport Zurich shows that CO₂ savings are significant.

Specific CO₂ emissions (kg/h) of APU, GPU and fixed electricity with the emissions from Swiss electricity production.

Airport Emission Savings per Year

The study further analyzes the total airport NOx and CO2 emissions in 3 scenarios:

1. Only APU usage
2. GPU and FEGP usage (currently in place)
3. APU is only used for main engine start rest is FEGP usage

The tables below show the result whereas the first column is scenario 1, the second is scenario 2 and the third is scenario 3.

NOx Emission Scenario Analysis

CO2 Emission Scenario Analysis

Cost Savings of GPU/FEGP per Hour

The study further analyses the cost savings for different aircraft with the current system in place (scenario 2, with GPUs and FEGO and PCAs) in comparison to scenario 1 (APU only).

• B764: Savings of 540 CHF per Hour
• B788: Savings of 614 CHF per Hour
• A321: Savings of 92 CHF per Hour
• B739: Savings of 115 CHF per Hour

It becomes obvious that the saving is significant for all 4 considered aircrafts.

Reducing APU Usage: How Video Analytics can help

Even when an Airport has FEGP and PCA installed, there are opportunities to reduce APU usage further.

The APU only gets switched off after FEGP is connected and the connection process can take some time. With Video Analytics the process can be monitored to send alerts to ground handlers when FEGP connection takes longer than expected.

The longer FEGP is connected to the aircraft, the better. Monitoring the disconnection process with video analytics can help to optimize the time.

Last but not least, the APU must be switched off by the pilot. Microphone sensors can be used to recognize when the APU does or does not get turned-off.

Further Reference:

• Auxiliary Power Unit (APU)
• Aircraft Ground Energy Systems at Zurich Airport, Emanuel Fleuti, Christian Ruf
• AVIATION OPERATIONAL MEASURES FOR FUEL AND EMISSIONS REDUCTION WORKSHOP, Aircraft Operating Procedures to Reduce Airport Ground Emissions, Captain Richard Sowden, Project Pilot Air Canada Flight Operations, Technical Group