More Power Feeder Problems

Please reference rotate.aero/forum/ata24-767/343-ata-24-2...ed-power-feeder-wire for some of our previously encountered problems.

Another power feeder wire short. This time the problem was inside the pressure vessel, as we normally find these on the engine or pylon.

The BPCU (Bus Power Control Unit) faults are always the same, DP Trip (Differential Protection) and GEN/FDR Fault (Generator/Feeder).

System isolation is the first step in troubleshooting. The feeder wires from the engine IDG (Integrated Drive Generator) go to the generator contactor. There are some extra wires connected to the three big feed wires. Three (one for each phase) go to the Generator Control Unit or GCU. Removing the box from the rack isolates those wires. Two extra wires, one for a red "Bus Hot" light and a EICAS voltmeter input also need to be separated from the feeds. Removing the bulb and pulling the breaker will accomplish that.
  
     
     
  
Using the megger from the generator end, we found the blue wire with the short.
  
     
  
No registered meter scale and less than 1 Meg-Ohm resistance. (The meggar picked this up as a hard short, but a regular VOM showed an open circuit.)
  
       
  
We went ahead and removed the blue feeder from the contactor just to make sure nothing else was in the system. The reading was the same.
  
     
  
We shook all over the engine and pylon with the megger on..... no joy. Same thing with some wing leading edge panels removed. (Two hours or more)

When we started shaking the wires in the right side forward lower cargo deck, the meter started jumping.

I wonder why....
  
     
     
     
     
  
Fun Stuff!!!