distances between drives and motors, multiple motor application, 4x 750 foot runs

[MICHAELGALLANT]

I was working on a drive application with 2 evaporators that have 2 motors each coming from the same feeder. All 7.5 hp at 600vac on the same drive, 750 foot runs... I know the voltage spikes can be up to 2400v and I am concerned that the existing cables will cause the motor insulation to burn out quickly. I was looking at sine wave filters but I dont believe it will address the cable insulation & motor insulation degrading quickly. I know VFD shielded cables are a good bet but I was told that the existing cables would not be changed. I believe the motors and cables will fail quickly, even using sine filters. I wanted to know how to calculate the insulation degrading factor on the total 3000ft distance of the 750 foot runs in order to show a comparison VFD cables to standard cables to reduce damage to cables and motors.

 

[Dennis Alwon]

Any help here.

 

[petersonra]

Any help here.

I don't know that you can calculate the magnitude of the problem.

 

[weressl]

I was working on a drive application with 2 evaporators that have 2 motors each coming from the same feeder. All 7.5 hp at 600vac on the same drive, 750 foot runs... I know the voltage spikes can be up to 2400v and I am concerned that the existing cables will cause the motor insulation to burn out quickly. I was looking at sine wave filters but I dont believe it will address the cable insulation & motor insulation degrading quickly. I know VFD shielded cables are a good bet but I was told that the existing cables would not be changed. I believe the motors and cables will fail quickly, even using sine filters. I wanted to know how to calculate the insulation degrading factor on the total 3000ft distance of the 750 foot runs in order to show a comparison VFD cables to standard cables to reduce damage to cables and motors.

Seriously consider of moving the drive closer to the motors. The reduced cable cost will cover extras for teh hardened or even purged enclosure for the drive.

There are also drives availabe with near-sine-wave output that solves the problem.

 

[ptonsparky]

I would think radio control with the VFDs at the load would be a simpler solution.

 

[__dan]

I was working on a drive application with 2 evaporators that have 2 motors each coming from the same feeder. All 7.5 hp at 600vac on the same drive, 750 foot runs... I know the voltage spikes can be up to 2400v and I am concerned that the existing cables will cause the motor insulation to burn out quickly. I was looking at sine wave filters but I dont believe it will address the cable insulation & motor insulation degrading quickly. I know VFD shielded cables are a good bet but I was told that the existing cables would not be changed. I believe the motors and cables will fail quickly, even using sine filters. I wanted to know how to calculate the insulation degrading factor on the total 3000ft distance of the 750 foot runs in order to show a comparison VFD cables to standard cables to reduce damage to cables and motors.

Maybe a typical application for a line reactor immediately adjacent to and at the output of the drive. Then the long load run maybe OK. Someone here will know better.

 

[MICHAELGALLANT]

drives

drives

Seriously consider of moving the drive closer to the motors. The reduced cable cost will cover extras for teh hardened or even purged enclosure for the drive.

There are also drives availabe with near-sine-wave output that solves the problem.

Hi Friend,

it's in freezer units, the cost offset of NEMA 4X heated enclosures and new cable runs from exisiting are high priced solutions. I was surprised that active harmonic filters could not be incorporated. I was thinking maybe bypassing to drive loads through secondary resistors connected to the load for the feed back that could be offset by a harmonic filter plus or minus? could be an intresting solution..... any thoughts?

 

[petersonra]

Hi Friend,

it's in freezer units, the cost offset of NEMA 4X heated enclosures and new cable runs from exisiting are high priced solutions. I was surprised that active harmonic filters could not be incorporated. I was thinking maybe bypassing to drive loads through secondary resistors connected to the load for the feed back that could be offset by a harmonic filter plus or minus? could be an intresting solution..... any thoughts?

your best bet would be to call the tech support people for the drives you will be using and ask them. this is often different for different drive lines.

I think in the end it will be cheaper to move the drives.

if you insulate the boxes you won't have to worry about heat much. VFDs put out a fair amount of heat even when inactive.

 

[Cow]

Hopefully Jraef will see your post. He's pretty knowledgeable on this stuff.

 

[mike_kilroy]

I would go for it with output inductors on both. If it was my design I would use a vfd that comes from a company with massive long output wire experience such as spindel in MI, as well as one with better than normal pwm smoothing as they also have. Someone needs to evaluate the potential voltage drop along that length of wire to determine even if an output reactor with its associated voltage drop is feasible Someone needs to evaluate the motor insulation system to be sure it is up to the challenge. Long leads lead to potential standing waves that can increase the 2x dc bus voltage spikes. Fortunately there is a theoretical max increase from this (3-3.5x dc bus IIRC) so the really really long cables are not really that much worse than say 100' in my opinion. My experience with insulation failure from voltage spikes tells me most good vacuum impregnated motors can handle up to about 2300-2400v before damaging erosion begins from ozone build up.

 

[kwired]

Hi Friend,

it's in freezer units, the cost offset of NEMA 4X heated enclosures and new cable runs from exisiting are high priced solutions. I was surprised that active harmonic filters could not be incorporated. I was thinking maybe bypassing to drive loads through secondary resistors connected to the load for the feed back that could be offset by a harmonic filter plus or minus? could be an intresting solution..... any thoughts?

How high price as compared to doing nothing and changing motors frequently? As said VFD's put out their own heat, even when not loaded. For the kind of distance you are talking about I think you could even build a non cooled control room of some sort somewhere closer for a reasonable price, but then again I don't know all the in's and out's of your application. Your problem is not a harmonics issue, it is as you mentioned a high voltage reflected wave. Not only will it cause motor problems, but if it reaches levels you mentioned will likely also cause conductor insulation failures at some point, also making your heated NEMA 4X enclosures look cheaper down the road.