Which statement accurately describes typical aircraft power system voltages and primary uses for DC and AC power?

Which statement accurately describes typical aircraft power system voltages and primary uses for DC and AC power?

• A. DC power is about 28 V for starting, battery, and most avionics; AC is 115 V, 400 Hz for main power distribution, engines, and avionics with rectifiers to DC as needed
• B. DC power is 115 V for lighting; AC is 28 V, 60 Hz for propulsion and avionics
• C. DC power is 28 V for cabin lighting; AC is 400 V, 50 Hz for engines and avionics
• D. DC power is 28 V for engines; AC is 230 V, 60 Hz for main distribution and avionics with rectifiers to DC as needed

Answer: (A)

Power systems on most aircraft are built around two voltage domains: a low-voltage 28 V direct current (DC) system and a higher-voltage alternating current (AC) system at 115 V, 400 Hz. The 28 V DC side is used for starting the engines, providing battery power, and feeding many avionics and DC-powered components. The 115 V AC at 400 Hz side is used for main power distribution and loads that run on AC, with engine-driven generators supplying this AC power. When DC is required by equipment, rectifiers are used to convert the AC to DC to feed the DC buses. The 400 Hz frequency is chosen because it allows lighter, smaller transformers and motors, which helps save weight—crucial in aviation.

Power systems on most aircraft are built around two voltage domains: a low-voltage 28 V direct current (DC) system and a higher-voltage alternating current (AC) system at 115 V, 400 Hz. The 28 V DC side is used for starting the engines, providing battery power, and feeding many avionics and DC-powered components. The 115 V AC at 400 Hz side is used for main power distribution and loads that run on AC, with engine-driven generators supplying this AC power. When DC is required by equipment, rectifiers are used to convert the AC to DC to feed the DC buses. The 400 Hz frequency is chosen because it allows lighter, smaller transformers and motors, which helps save weight—crucial in aviation.