As for the AC Emergency and DC side of things...
AC Emergency Generation and Distribution
A static inverter is supplied from the DC essential busbar via a static inverter control relay, and connected on its AC output side to the AC essential busbar via an AC change-over relay.
A STATIC INVERTER TEST switch and a magnetic indicator (MAIN, amber, INVERT) are provided which, in conjunction with the AC change-over relay, enable the static inverter to be tested.
During normal operation the static inverter is isolated from both busbars; the AC essential busbar is supplied from No.1 AC main busbar, and the magnetic indicator displays MAIN. If power fails on the No.1 AC main busbar, or the test switch is held in the TEST position, the static inverter is automatically brought into operation to maintain the AC essential busbar and the magnetic indicator displays INVERT.
DC Generation and Distribution
The main DC power supplies are normally provided by No.1 and 2 TRUs which are supplied from the No.1 and No.2 AC main busbars respectively. The output of No.1 TRU connects directly to the 28V DC essential busbar and the output of No.2 TRU connects directly to the 28V DC main busbar.
Power for starting the APU and, if both TRUs fail, maintaining the essential services, is provided by two 24V batteries which are connected in parallel to a battery busbar.
When the DC essential and the DC main busbars are 'live' they are automatically interconnected by a main busbar isolation relay. The DC essential and the battery busbars are normally interconnected, via a battery isolation relay, through operation of a control switch (BATTERY) on the roof panel. The battery isolation relay can also be closed by selecting either the fuel load control switch to ON or the DC hydraulic pump switch to BRAKE ACC. A BATTERY MI is provided to indicate (OFF) when the battery busbar is disconnected from the DC essential busbar.
During normal operation all three DC busbars are interconnected, but if the busbar voltages fall below approximately 24 volts, the main busbar isolation relay is automatically opened to isolate the DC main busbar. Thus, if both TRUs fail, the DC essential and the battery busbars are maintained by the batteries. A red DC FAIL warning light gives a visible indication when the DC main busbar isolation relay is open, thus indicating a DC failure. This light is connected to the master warning system.
A DC voltmeter (DC VOLTS) is normally connected to the DC main busbar and therefore normally shows the voltage on this and the DC main busbar. The PUSH FOR BATT VOLTS button transfers the voltmeter to the battery busbar thus showing the voltage on this provided the battery switch is OFF. Otherwise the voltage will be the same as if the button were not pressed. Each TRU has an associated ammeter (TRU AMPS) which indicates the current the respective TRU is supplying to the system. A single charge/discharge ammeter (BATT AMPS) serves both batteries.
TCF