Transformer Rectifiers
Used to produce DC power and electrical supply for DC buses. Similar to an inverter.
The aircraft is equipped with 3 TRs. They convert 115v AC power to 28v DC power.
TR 1 receivers power from AC Transfer Bus 1; TR 2 from Transfer Bus 2.
Normally, TR 2 is powered from Transfer Bus 2. However, in the event of a power loss it can receive power from Transfer Bus 1 via the Cross Bus Tie Relay. This switch occurs automatically.
The TRs normally power DC Bus 1 and 2, DC Standby Bus, and the Battery bus. TR 3 is primarily used to supply power to the Battery bus and as a back up for TR 1 and 2.
Any 2 TRs are capable of supplying the total connected load. Note, however, that 2 TRs on opposite sides of the Cross Bus Tie Relay are needed during an ILS upon glideslope capture.
In flight, a TR unit annunciator light indicates:
- TR 1 failed, or
- TR 2 and TR 3 failed
On the ground the light indicates that any TR fault has occurred.