Damaged 110 kW motor

[maypot]

Hi,

One 110 kW inverter fed 400 V motor got damaged, after a couple of weeks of operation , due to insulation failure. The motor was fed through one hundred metres of cable and I presumed the motor winding got stressed due to the successive peak wavefronts -the so called voltage doubling reaction.
However, another motor 100 kW capacity , also inverter-driven, and also fed from about 100 metres of cable is operating well since years-five to six years.
I am requesting my management to install output reactors on both drives but they do not believe this argument as the 100 kW is operating without any problem. I am stuck but
I am convinced that the 100 kW will burn sooner or later.
According to literature, the peak voltage on the terminal of the motor should be around 212 % the DC bus voltage i.e 1260 V which is too much for a 10OO V insulation class motor.
Any suggestion.

Bob

 

[jraef]

Are the motors the same manufacturer and the same design? Some motors are available with newer insulation systems that are good up to 2000V. This has been around as an option long enough for your 100kW motor to possible have it, and perhapse your other motor did not, even if it was newer. It does not mean that the peak voltages are not happening in the 100kW system, it just might be that the motor is more resistant to it.

Also, is it the same VFD manufacturer and design? some VFDs have filtering already built-in, so an output reactor would not necessarilly be necessary.

"Venditori de oleum-vipera non vigere excordis populi"