Toasted windings in 3 phase motor...

[Externet]

Hi.
Replaced a burned 2HP 400Hz motor and after dismantling wiring, found one phase wire at the power relay with open solder joint.
Would that be the cause for the motor failure ?
The overcurrent at failure moment could have also had melted the solder, right ?
Any other probable reasons that you may suspect ?

 

[Harald Kapp]

Is the failed joint on the burned winding or another one?

If on the burned winding, the overheated winding could have caused the joint to melt.
If on another winding, the joint could have melted, thus bereaving the motor of one of its 3 windings. This loss would have reduced the rpm of the motor, thus creating less counter emc in the remaining windings which in turn would have increased the current there and this power consumption. The result being a burned winding. Just speculating.

I wonder why no external motor protection was triggered.

 

[Minder]

Would this be a 24k rpm H.S. spindle by any chance?
Ran off of a VFD?
Or if another 400hz source, any poor/high-resistance joint creates heat.
But as per H.K. why was not a phase loss detected?, usually by O/L trip
M.

 

[Externet]

Thanks. All windings are 'carbonized' , the open failed solder is at one relay pin. No fuses, no breakers in the assembly; perhaps very externally. Military equipment.
IF protection circuitry was triggered, it was in the 'Murphy's law style' : "Expensive equipment blows itself first to protect the fuse"
No VFD. 11500 rpm. Compressor drive.

 

[Minder]

Where is the 400hz supply from?
M..

 

[Externet]

Generator in airplane.