If one TRU is offline, what happens to DC power on the DC buses with two TRUs installed?

If one TRU is offline, what happens to DC power on the DC buses with two TRUs installed?

• A. The remaining operative TRU maintains power to the DC buses.
• B. All DC power is instantly lost.
• C. The standby power system powers the DC buses.
• D. The APU powers DC buses.

Answer: (A)

Redundancy in the DC power system is provided by two Transformer Rectifier Units feeding the DC buses in parallel. When one TRU goes offline, the remaining operative TRU continues converting AC to DC and powers the DC buses, so there is no loss of DC power. The standby power system only takes over if all main sources fail, and the APU’s power would not be required to cover a single failed TRU under normal operation. In short, as long as one TRU is online, it maintains DC bus power.

Redundancy in the DC power system is provided by two Transformer Rectifier Units feeding the DC buses in parallel. When one TRU goes offline, the remaining operative TRU continues converting AC to DC and powers the DC buses, so there is no loss of DC power. The standby power system only takes over if all main sources fail, and the APU’s power would not be required to cover a single failed TRU under normal operation. In short, as long as one TRU is online, it maintains DC bus power.