Aircraft Electrical Power Distribution Systems
Passenger aircraft require reliable power distribution systems to carry out their operation and take hundreds of passengers across thousands of miles. Each aircraft has multiple sources of power and corresponding distributors. On average, airliners feature two or more AC generators driven by turbine engines. DC systems are also present on large aircraft to supply emergency power in case of main generator mishaps.
Transport category aircraft use large amounts of electrical power for many different systems. The passengers alone need significant electrical power for comfort-enhancing features like lighting, audio visual systems, food warmers, and beverage coolers. Electronics are also needed to fly the aircraft in flight control systems, engine controls, communications, and navigation systems. The complexity of having multiple generators and a variety of distribution buses requires several control units to ensure a constant, safe supply of electrical power. Aircraft electrical systems must maintain an output between 115 and 120 volts while not exceeding power limits.
On a large passenger aircraft there are typically two electronic line replaceable units controlling the electrical power. The generator control unit (GCU) is tasked with maintaining AC generator functions like voltage control and frequency regulation. The bus power control unit (BPCU) takes on the role of distributing electrical power evenly between the differing distribution buses on the aircraft. The GCU and BPCU work in tandem to control power, find faults, take corrective actions whenever necessary, and report those faults to the aircraft’s central maintenance system.
The BPCU also monitors the system through the use of remote current sensors known as current transformers. A current transformer (CT) is an inductive unit that surrounds main power cables within the electrical power distribution system. When AC power travels through the main cables, the CT receives an induced voltage. The amount of voltage is tied to the current flowing through the cable. The CT connects to the BPCU, allowing accurate monitoring of the system. The average aircraft has several CTs in use.
