Which statement best describes DC power supply in this system?

• A. DC Power Is Supplied By Four Transformer Rectifier Units
• B. DC Power Is Supplied By A Single TRU
• C. DC Power Is Supplied By External Power Only
• D. DC Power Is Supplied By The APUs

Answer: (B)

DC power in this system comes from a Transformer Rectifier Unit that converts AC to the DC the system uses. The correct statement says there is a single TRU supplying the DC power. This means the DC bus is powered by one internal source, which is enough for normal operation and keeps the design simple and cost-effective. If more DC current or redundancy were needed, the system might parallel additional TRUs or use other sources, but that would be a different configuration.

Think of the alternatives: four TRUs would imply more internal redundancy and capacity than the system requires; relying only on external power would mean no internal DC generation at all; having the APUs supply DC would tie the DC power to the APU’s operation, which isn’t what this system uses. The single TRU arrangement matches the described design, providing the needed DC while keeping the setup straightforward.