Driving a motor 250m away

[redeemer 0]

Hi, I have an application where I use a frequency inverter to drive a 7.5hp motor located 250 meters away from the drive. Speed changes are not very rapid (in the order of one minute). When choosing the drive and cable, are there any special requirements due to the long distance between motor and drive? Or is it enough to choose a drive with a compatible power rating and a suitable cable according to the max current? Electro-magnetic emissions are not an issue in this application. Regards, Fadi

[BobLfoot 302]

AB has a complete manual and set of recommendations for "long wire" drive applications. You'll definitely have line loss and standing wave issues to engineer around. As an alternative have you considered a "ruggedized drive". AB makes a VFD with IP67 rating, jsut run your 3 phase and DNET cables to it. Used several of these on a warehouse job a few years ago.

[panic mode 246]

call manufacturer of the drive. they should be able to give you tools and assistance needed to size this for particular drive and motor. tipically your drive will need to be larger to handle loses, this can be partially minimized by using non-shielded cable for example. on a similar job but with servos and with 400ft long cables (about 130m) we had to practically double drive size and cables had to match the drive of course.

[redeemer 0]

This is very interesting. I tried to find this information on ww.ab.com, but couldn't. Do you have a link or a keyword, I would be grateful. Fadi

[redeemer 0]

We haven't talked with a manufacturer yet, we are still in the planning phase. And we were looking into the things that should be taken into account. And it's an opportunity to learn. In your response you mentioned using a non-shielded cable. What's the point? I feel I'm missing something here.

[P Daniil 0]

The motor construction and insulation should also be for use with an inverter . Non-inverter grade motor insulation and bearings will wear out quickly because of the long cable effects. Also, using a lower inverter switching frequency will not do much as it is the PWM waveform rise- and fall- time which cause the problem. Using a ruggedized drive (as BobLfoot suggests above) will also save you potential protective earth problems such as cable leakage causing fault trips and similar troublesome return currents.

[panic mode 246]

any decent vfd manual will tell you what length cable you can use and max length for unshielded cable is always greater (considerably). shielded cables have higher loses and cannot run as far (unless you beef up the drive and cable to compensate for loses). as already mentioned, make sure to use proper cable (vfd rated) because the longer the cable, the higher voltage spikes.

[paulengr 44]

Watch out! With long cables like this, you can get standing waves forming in the cable because the cable is becoming electrically "long" relative to harmonics generated by the drive. The standing waves can cause hot spots which will burn through the cable insulation. In addition you can get harmonics which will destroy the motor bearings by etching it. Contact AB before you do this because it just requires some planning (and filtering) to avoid these nasty problems. Better yet if possible, move the drive closer to the motor.

[BobLfoot 302]

Took about 2 minutes to locate the Wiring and Grounding Guidelines for Pulse Width Modulated (PWM) AC Drives I see application data for lengths out to 300 and 400 meters.

[jhughes 1]

I worked in a facility where we were driving several 25 and 30 hp motors at 300 feet (AB 1336 Plus). CABLING will definitely make a difference. We had reflected wave issues causing high currents before we changed to mfg spec's cables and grounding properly. Also spending the time to tune the motor helped us lower our amperage.