Electrical Interference while using VFD 3

[structure59]

Hi,
I am facing a problem of electrical interference in sidescan sonar winch of an oil/gas exploration vessel. Can anyone suggest a solution please?
1. The equipment sidescan sonar operates in ship supplied through DG power 415 Vac, 50 Hz, 3ph
2. Winch has option of operating in VFD mode and manual mode through contactors. Pay-in pay-out of winch rope is controlled better in VFD mode.
3. Main problem is when the winch motor or the guider motor is operated through VFD, the data communication to the Top unit halts and after few seconds gets disconnected. However when operated in manual mode, the communication is smooth and uninterrupted.
4. Presence of voltage harmonics seen in VFD circuits. These values are quite higher in guider 1 HP motor, as high as 24% ( Vthd )
5. Power consumption is very less in VFD mode compared to manual mode. Current drawn in VFD mode is 4 to 6 A as compared to 21 A in manual mode. Also at start in manual mode inrush current is as high as 170 A. this is for few seconds and then normalizes to 21 A .

Thank you in anticipation.

 

[RedSnake]

The basic rules are that the motor cable must be shielded and the shield must be unbroken between the VFD and the motor and connected to the potential earth in both ends.

The same trules goes for a communication cable it should also be shielded and the shield potentially grounded in both ends depending on type of communication bus this is usually already done through the units but this only works if the cabinet itself is properly grounded.

This two cables should not be in the vicinity of each other, they should not be bundled together and they should not cross each other in a X way.

NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[FacEngrPE]

Eaton's recommendations for wiring VFD's

https://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/ap040076en.pdf

If your already have shielded marine grade power wiring, verify that all of the cores feeding the motor are inside the same shield, the shield is electrically connected to the motor frame at the motor junction box, and that the shield is electrically connected to the VFD (or VFD enclosure) in the manner recommended by the VFD manufacturer. Also check for the items Anna indicates, they are important.

 

[Gr8blu]

To start with, it sounds like your VFD is controlling the operation of the winch at a much lower speed than the manual contactor approach (regulating at around 6 A or so vs what I suspect is full NP at 21 A for the contactor approach). This means the drive is acting in a "phased back" condition - which will result in far higher V- and I-thd values, compared to operation at a "full power" point. Remember, drives are usually optimized for their nameplate ratings, too.

Second detail is - as Anna noted - the power and control cabling for the winch are almost certainly run in close proximity ("close" in this context means within about 6 inches of each other). As a result, the harmonic content and associated "spikes" in the magnetic field around the power cable(s) is creating cross-talk which is disrupting the low-amplitude signal of on the communication line. Proper shielding - and proper termination of the shielding - can go a long way to mitigating the problem. Moving the communication lines to another (more distant) run will also help.

By the way - if you really are putting out a total Vthd in the 20+ percent range to the motor, chances are the winch motor isn't going to last all that long, either. The insulation system wasn't designed for the voltage spikes - and the only saving grace is that the operation is at a very reduced current/speed point, otherwise it might fail on thermal degradation.

Converting energy to motion for more than half a century

 

[LionelHutz]

they should not cross each other in a X way.

I think you mean the power and control cable types should only cross in an X way.

regulating at around 6 A or so vs what I suspect is full NP at 21 A for the contactor approach

You really can't determine output speed when just looking at input current levels. I doubt the motor FLA is 21A, I bet it's more like 30-40A since the starting current reaches 170A and the generator is likely weak enough to be limiting the current well below the datasheet LRA.

This means the drive is acting in a "phased back" condition - which will result in far higher V- and I-thd values

You are talking on the input side, right? On the input side the percentage distortion might be higher at low loads, but the harmonics will be at lower amplitudes and interference is caused by the amplitude of distortion, not the percentage of distortion. I don't think you'd be talking about the output side since the distortion on the output side is bad at any VFD speed.

 

[RedSnake]

I think you mean the power and control cable types should only cross in an X way.

Both yes and no.

What I meant was that since these two cable types should not be put together at all, you should strive to never cross them at all.

Which is the basic rule.

Since structure59 didn't leave much info on the status of the cables, I didn't feel it was necessary to go into all the finer details.

But if you still end up having to cross them, you should not cross them in a X way but in a 90 degree angle way like a "plus" +.


NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[LionelHutz]

So, an X rotated 45 degrees.

 

[RedSnake]

LOL

Maybe you are using a different font than me, because my large X has not got 90 degree angles between the "lines".


NAFO Sergeant Anna Gr 69th Sniffing Brigade

 

[structure59]

Thank you friends for your valuable inputs. Shall revert after sometime.