VFD Power Supply Cable Fault

Fuses blow to protect cables from overheating and starting a fire.

It sounds like your cables were too hot.

Find out why.

Sounds like the problem is the VFD. It probably has been drawing too much current for a long time. Don't just replace the cable, check the VFD. Start by measuring how much current it is drawing.

Would a line reactor help?

A difference in cable insulation type and rating or because the cable conductor size is too small or borderline for the amperage it is carrying which is causing too much temperature rise resulting in cable insulation heat damage.

It sounds as though the cables are undersized. Have the installation checked out by a qualified Electrical Engineer, who will re-size the cables based upon local electrical codes and recommend replacement if necessary.

You said..

Had a cable fault on two cooling water tower fans today,~

I'm guessing these towers are outside exposed to the elements.... how long they been installed?

You could be looking at natural (or un-natural) weathering of the cable that is not suited to outside use, (heat, sun, rain & cold??) or it needs extra protection against the weather.

Hi,

Thanks for your answers.. but the cable is not undersized.. the current drawn by this VFD and motor is about 39 amps, a cable calculations indicate that a 10mm cable would be ok but recomend 16mm. I am using a 25mm cable.Cable run is about 90 meters. - not very long..

I was thinking about harmonics generated by the VFD, but I do not know mush about them. was looking for some advise.

Regards

Harmonics.. you need a Power Quality analyzer. Try Fluke!

To overcome any harmonic output you MIGHT have.. and that could be dependent on type of VSD and the distance/length of cable between VSD and motor, could be of such a small value/distortion %, that a filter might not be worth buying.

Also Harmonics would have an adverse effect on the motor rather than on the cable, unless you have a splice or joint in that cable. Again the length of the cable has a bearing on this.

You need to speak to your VSD supplier and ask them.. they might be able to advise in regards to harmonic output and filters suitable for the VSD you have.

I still think your cable has weathered due to the climate conditions.. try not to overthink this!

Are you sure that the insulation rating is compatible with the chemicals used in the cooling tower? It may be the water purification and hardness control chemicals are attacking the cable insulation.

90m is not short either.

What is the calculated voltage drop?

Is the voltage into the VFD the same as the voltage to the fans? A lower voltage means a higher current for the same amount of power.

Are the wires to the VFD enclosed where any heat generated is trapped?

Was the wiring to the fans replaced more recently than the wiring to the VFDs?

You state the load side cables are fine but both line sides are deteriorated. Are the line cables in sunlight or have loose connections; are the load sides coated by minerals or sludge?

Good luck.