Main bus tie
Hi.
What utility main bus tie switch ?
Why on before start engine,off after start engine,on after landing ?
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Hi.
What utility main bus tie switch ?
Why on before start engine,off after start engine,on after landing ?
Comments
From Airliners.net forum:
Airliners have several different electrical busses ( a `"bus" is an electrical distribution bar, picture a strip of metal with rows of circuit breaker coming off of it.)
For safety and redundancy they are split up so a failure of one bus does not black out the aircraft. For example, the Dash 8 has a left (L) and right (R) Main bus, L+R Secondary, L+R Essential, and a Battery bus, also L+R AC Variable Frequency busses, AND L+R 115 ac and L+R 26volt AC. Thats 13 busses not counting assorted feeder busses.
As for the bus tie switch, under normal operation, the LH DC generator will power the LH busses, and the RH gen the RH busses. This avoids the need to balance the generator outputs. If a generator fails, or the engine fails, the busses should automaticall "tie", or connect together so one gen owers both. If this does not happen, the bus tie switch will do the job.
AC vs. DC; Ac is great for a lot of jobs like motors, heaters, pumps, etc, but some things prefer DC. Electronics usually need both, and the thousand or so relays in the aircraft use DC for their coils. Typically, a large airliner is mostly AC with some DC. Smaller types such as the Dash 8 100-300 are mostly DC with some AC.
from minute 11:50 your question should be answered
To make it simple:
Each engine has a generator for each battery and circuit.
In case of engine failure and/or generator failure on one engine the batteries are linked together automatically.
If this automatic link does not work you would loose electrical power so you "tie" the electrical circuit manually together with the Bus Tie switch.
Some operators taxi with only one engine and if something goes wrong in the electrical circuit all the screens will go "black".
This Bus Tie switch is there "just in case".
Same with the fuel pumps or the hydraulics ; you switch manually ON in case of there is some kind of failure. If everything was going fine with no risk of failure we would have barely no switches in a cockpit.
JP
The DASH uses what's called a split bus system with the respective generator powering it's associated generator. The bus tie allows you to power the opposite bus if it's power source were to fail. This is done automatically by the EPCU.
Not sure what's the etiquette on this forum, but I wanted to say I appreciate the explanations too. I was trying to figure out this for long time.
THANKS!
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