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For A330, may I know why is the DC BAT BUS supplied for approximate 7 seconds in the BAT only configuration? From the FCOM, during the 7s, the DC BAT is supplied directly by the BAT 1/2 through the BCL charging contactors (6PB1/2, I believe).

Some say it is the time for the CSM/G to speed up. But the CSM/G is to mainly supply DC ESS (through the TR ESS). Even after the CSM/G is speed-up, the DC BAT will not be supplied any more, so it's not that important. Also, even during the BAT only config, the BAT 1/2 can supply DC ESS directly, so it's not needed to supply the DC ESS through the DC BAT (by the DC ESS TIME Contactor 4PC).

Any people know why is there a 7s momentarily supply? Is it related to some of the equipment connected on DC BAT that it is crutial during the 7s? What makes the DC BAT so important that it is powered only 7 seconds, but not that important after?

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  • $\begingroup$ From the documentation online, I believe this is the time required to deploy the RAT in case both engines are lost. When the RAT is deployed it pressurizes the GREEN hydraulics powering the emergency generator. In the meantime batteries feed the DC bus which is used to generate AC. Does that make sense? $\endgroup$
    – mins
    Commented Aug 25, 2024 at 18:28
  • $\begingroup$ @mins Not really, that's similar to what someone said for the CSM/G to spool up. If the DC BAT is so important, it should still be powered, by the CSM/G, after 7 seconds, after the RAT deployed and CSM/G spooled up. That means the first 7 seconds by the Bats and the CSM/G will power the DC BAT later. But it's no designed like this. CSM/G will only power DC ESS, not including the DC BAT. May be I should rephase my question, what makes the DC BAT so important that it is powered only 7 seconds, but not that important after? $\endgroup$
    – Jono
    Commented Aug 26, 2024 at 1:47
  • $\begingroup$ My attempt to read this schematics is (when on batteries) DC ESS is fed by the batteries and DC BAT too using BAT contactor during 7s. After 7s DC BAT is isolated from batteries but is now fed by the CSM/G thru TR 1/2 and DC 1/2 buses. Is it correct? If so, DC BAT is always fed unless DC TIE is opened, I don't get the behavior of this switch in this process (sorry for the multiple edits of this comment, I hope you escaped it). $\endgroup$
    – mins
    Commented Aug 26, 2024 at 8:50
  • $\begingroup$ @mins when the CSM/G kicks in, TR1/2 will be (already be) dead and so DC1/2 will also be dead. So DC BAT will no longer be powered after 7 sec, no matter it's the BAT-only config, EDP driven CSM/G config, or the RAT driven CSM/G config. $\endgroup$
    – Jono
    Commented Aug 26, 2024 at 14:26
  • $\begingroup$ I must miss something, AC 1/2 are certainly lost when CSM/G starts, hence TR 1/2 are certainly unpowered, I agree. But I don't see why CSM/G wouldn't repower TR1/2 as soon as it is operational, it's the goal. $\endgroup$
    – mins
    Commented Aug 26, 2024 at 15:34

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