Post by LOU on Apr 20th, 2015 at 5:14pm
MKA742 stated:
What I also noticed just recently;
1 Select ground power as you should (switch on EXT, close breaker)
2 Open the engine generator breaker switches
=> No power??
Makes no sense to me :p
The 707 & 727 electrical panel work pretty much the same way.
In this picture I opened the GEN BREAKERS to show how it SHOULD look.
You cannot have two types of electrical power at the same time.
*You have engine driven generators
*External power
*APU if equipped
Only one of these sources at a time will work.
The way it should work is lets say you have just pulled into the gate and the engines are still running, the ground power is plugged in. The F/E selects external on the meters selector switch. If the voltage and frequency are within limits the F/E then selects ON by closing the external selector switch. As the switch is moved to the close or ON position the first thing that happens is a signal is sent to trip the MGR (main generator relay) on the F/E panel which is labeled GEN BREAKER. It is the middle switch on the electrical panel. This trip must happen before the external power relay closes to prevent multiple power sources. The same is true in reverse, if external power is on and the engine is started, the closing of the GEN BREAKER will first trip the external off so as to avoid two sources at the same time. The engine driven generators are considered the same power source since they go through the BUS TIE BREAKERS which provide sync bus protection.
Now the rub... this is not modeled correctly in the 707 or 727 in that the GEN BREAKERS do not illuminate when power is changed over. This does not seem to affect power to the plane, but is not correct.
Lou Â
What I also noticed just recently;
1 Select ground power as you should (switch on EXT, close breaker)
2 Open the engine generator breaker switches
=> No power??
Makes no sense to me :p
The 707 & 727 electrical panel work pretty much the same way.
In this picture I opened the GEN BREAKERS to show how it SHOULD look.
You cannot have two types of electrical power at the same time.
*You have engine driven generators
*External power
*APU if equipped
Only one of these sources at a time will work.
The way it should work is lets say you have just pulled into the gate and the engines are still running, the ground power is plugged in. The F/E selects external on the meters selector switch. If the voltage and frequency are within limits the F/E then selects ON by closing the external selector switch. As the switch is moved to the close or ON position the first thing that happens is a signal is sent to trip the MGR (main generator relay) on the F/E panel which is labeled GEN BREAKER. It is the middle switch on the electrical panel. This trip must happen before the external power relay closes to prevent multiple power sources. The same is true in reverse, if external power is on and the engine is started, the closing of the GEN BREAKER will first trip the external off so as to avoid two sources at the same time. The engine driven generators are considered the same power source since they go through the BUS TIE BREAKERS which provide sync bus protection.
Now the rub... this is not modeled correctly in the 707 or 727 in that the GEN BREAKERS do not illuminate when power is changed over. This does not seem to affect power to the plane, but is not correct.
Lou Â