[basskitcase]

I may be overthinking this because I regularly work with large VFD driven motors but is protection from common mode voltage needed for VFD spindles (I.e. shaft grounding) or is that generally not an issue? I am running a 2.2 kw Huanyang water cooled spindle off a Yaskawa V1000 drive in open loop vector mode with 8K carrier frequency. Cable is about 10 feet and isn’t shielded yet but will be. I am also thinking I should back off the carrier frequency a bit. Would other harmonic control methods like line reactors/chokes or ferrite cores be recommended?

[mactec54]

I may be overthinking this because I regularly work with large VFD driven motors but is protection from common mode voltage needed for VFD spindles (I.e. shaft grounding) or is that generally not an issue? I am running a 2.2 kw Huanyang water cooled spindle off a Yaskawa V1000 drive in open loop vector mode with 8K carrier frequency. Cable is about 10 feet and isn’t shielded yet but will be. I am also thinking I should back off the carrier frequency a bit. Would other harmonic control methods like line reactors/chokes or ferrite cores be recommended?

You want to change the spindle to VFD cable ASAP a line Filter is a good idea as for shaft voltage if you want your bearing to last then yes there is room in the cap at the top of the spindle to add a brush but will have to modify the top of the spindle I have done some and it works very well, the time to do it may not be worth the trouble to some as these spindles don't cost that much to replace

Cables I have used most, the best value and cable I recommend is this IGUS cable CF6-15-04

6k to 8k Carrier Fequency is a good number for these spindles

[CitizenOfDreams]

I have seen CNC routers with three 2kW spindles (and three VFDs) using plain unshielded cables without any issues whatsoever. I have seen a router with a 7kW spindle where one conductor in the factory installed shielded cable broke and was "temporarily" bypassed by a single unshielded wire - again, without any issues. I have seen a fleet of about 10 machines with VFD-driven high speed motors where shielded cables were replaced with regular ones - again, working day in and day out without an issue.

In other words, it is nice to have a good shielded cable on your VFD, but it is not an absolute necessity. Especially when the cable would cost almost as much as the VFD itself.

[Eldon_Joh]

The shield of the cable does nothing for the motor but lower the inductance of the cable slightly which would only matter for long cable runs. due to the square edges of the pwm out of the vfd, there is a voltage doubling resonant effect between the parasitic capacitance of the coils and the inductance of the cable. an rc filter at the motor can stop it, but it does nothing if it isn't a problem.


the common mode voltage delivered by the vfd looks like this
Attachment 410298

and you can't get rid of it without an LC filter. i made one from a standard line/load reactor, adding an extra mangetic path to it, you can then use 3 capacitors after the inductor, connected back to the negative (or positive) bus of the VFD.
Attachment 410300


you don't need to add the extra magnetic path to the reactor if you just want delta connected capacitors at the motor, and that will deliver sine wave phase to phase voltages, but that doesn't remove the common mode voltage from line to ground, which requires a 4 or 5 leg inductor. adding the extra magnetic path will increase the inductance of the choke which means the saturation current will decrease.. so keep that in mind.


anyhow i haven't seen anyone on this forum mention shorter bearing life without a shaft ground.

[mactec54]

I have seen CNC routers with three 2kW spindles (and three VFDs) using plain unshielded cables without any issues whatsoever. I have seen a router with a 7kW spindle where one conductor in the factory installed shielded cable broke and was "temporarily" bypassed by a single unshielded wire - again, without any issues. I have seen a fleet of about 10 machines with VFD-driven high speed motors where shielded cables were replaced with regular ones - again, working day in and day out without an issue.

In other words, it is nice to have a good shielded cable on your VFD, but it is not an absolute necessity. Especially when the cable would cost almost as much as the VFD itself.

It helps to have an understanding of correct electrical practice if you are going to post about something like this

With what you saw does not sound like it would of been a safe place to work, remember there are electrical codes to safe guard against installations like this, some 3Ph installations can get away with unshielded cable only in some cases, but not residential single phase installs, with single phase the noise generation is much greater because of the unbalanced power supply to the VFD Drive

It is a requirement by all VFD Drive manufactures to use shielded cable to be EMC compliant, if you can find a VFD manual that does not show this in there wiring then please post it here, there are some exceptions as with some of the cheap Chinese VFD Drives manuals, that you won't find good instruction on the use of shielded cable, common sense prevails when using these drives

[mactec54]

The shield of the cable does nothing for the motor but lower the inductance of the cable slightly which would only matter for long cable runs. due to the square edges of the pwm out of the vfd, there is a voltage doubling resonant effect between the parasitic capacitance of the coils and the inductance of the cable. an rc filter at the motor can stop it, but it does nothing if it isn't a problem.


the common mode voltage delivered by the vfd looks like this
Attachment 410298

and you can't get rid of it without an LC filter. i made one from a standard line/load reactor, adding an extra mangetic path to it, you can then use 3 capacitors after the inductor, connected back to the negative (or positive) bus of the VFD.
Attachment 410300


you don't need to add the extra magnetic path to the reactor if you just want delta connected capacitors at the motor, and that will deliver sine wave phase to phase voltages, but that doesn't remove the common mode voltage from line to ground, which requires a 4 or 5 leg inductor. adding the extra magnetic path will increase the inductance of the choke which means the saturation current will decrease.. so keep that in mind.


anyhow i haven't seen anyone on this forum mention shorter bearing life without a shaft ground.

The setup you have just shown would have a hard time being code compliant

Most don't know why there bearings failed, and either rebuild there spindle or buy another one, many have had bearing failure, not always because of rotor voltage though, this will happen over time to all of them, they have even blown Breakout Boards when using a touch off plate, for Tool touch off, shaft / rotor Grounding would of prevented this, most AC motor manufactures that have VFD rated motors already have Shaft / Rotor Grounds built into there motors some are an option for other motors also

[CitizenOfDreams]

It is a requirement by all VFD Drive manufactures to use shielded cable to be EMC compliant, if you can find a VFD manual that does not show this in there wiring then please post it here, there are some exceptions as with some of the cheap Chinese VFD Drives

OK. Siemens SED2 operation manual:
"Maximum motor cable length is as follows:
• 328 ft (100 m) for shielded cables
• 164 ft (50 m) for unshielded cables"

Siemens Sinamics S120:
"Max. motor cable length: 50 (shielded), 75 (unshielded)"

Siemens Micromaster 420:
"All inverters will operate at full specification with cable lengths up to 50 m screened or 100 m unscreened."

[mactec54]

OK. Siemens SED2 operation manual:
"Maximum motor cable length is as follows:
• 328 ft (100 m) for shielded cables
• 164 ft (50 m) for unshielded cables"

Siemens Sinamics S120:
"Max. motor cable length: 50 (shielded), 75 (unshielded)"

Siemens Micromaster 420:
"All inverters will operate at full specification with cable lengths up to 50 m screened or 100 m unscreened."

As I said in the last post you have to have an understanding of what the electrical requirement's are for a VFD Drive, what you have posted again shows you have no comprehension of what you are reading

Siemens have one of the strictest requirements for wiring VFD Drives which already have built in Filters to prevent a noisy environment, they also have some of the best examples, so I'm glad you picked Siemens

This is from the same manual SED2 Note even though they still are EMC compliant the still require to use Shielded Cable

This is what they say in there description from there manual for installation How could you miss this, This is the industry standard and in most countries a code requirement

Installation

The SED2 operates in environments where they may be exposed to high levels of electromagnetic interference (EMI). Normally, good installation practices ensure safe and interference-free operation. However, should problems associated with EMI occur, follow these guidelines: • Ensure good electrical contact between the mounting plate and the metal housing of the SED2 via the mounting screws. • Use serrated lock washers and electrically conductive mounting plates. • If a footprint EMC filter is used, fit it under the SED2 and ground it via the metal backplane. When connecting the EMC filter to the inputs of the SED2, use shielded cables, and ensure that they are correctly grounded using cable clamps (Figure 40).

Wiring

• Ensure that all equipment in the control cabinet is properly grounded. Connect all equipment by short, thick grounding conductors to a common grounding point or bus bar. • Ensure that any control equipment connected to a SED2 (such as PLC or BACS, programmable logic controller or building automation and control system) connects with a short, thick cable to the same ground or grounding point as the SED2. • Use shielded cables inside control cabinets. Use only shielded motor and control cables. The shielding must be continuous. Connect motor and control cables to ground at both ends. Avoid pigtails. Use only grounding clamps to bond the shield (Figure 40). • Lay control, mains, and motor cables separately by routing them in separate cable ducts and maintaining a minimum clearance of 7.8 inches (200 mm). See Figure 41. If you cannot avoid crossing cables, run them at a 90-degree angle.

[basskitcase]

You want to change the spindle to VFD cable ASAP a line Filter is a good idea as for shaft voltage if you want your bearing to last then yes there is room in the cap at the top of the spindle to add a brush but will have to modify the top of the spindle I have done some and it works very well, the time to do it may not be worth the trouble to some as these spindles don't cost that much to replace

Cables I have used most, the best value and cable I recommend is this IGUS cable CF6-15-04

6k to 8k Carrier Fequency is a good number for these spindles

Thanks all for your comments and recommendations, they have been helpful. I will be using shielded cable I just need to get things running before it arrived. It’s not very elegant but I have my spindle power cable dropping from the ceiling so it is pretty far away from other cables. Anyone have experience with ferrite cores or similar?

On the topic of shielded vs unshielded being proper and per code, what I can say, at least on the large HVAC equipment I work with is many cables are not shielded. EMC is dealt with using other methods such as having the cables in a metal raceway, so I think it’s fair to say that shielded cable isn’t always required but some form of mitigation for EMC is generally needed, whether that is in the form of shielded VFD cable or not. Also I don’t see much attention paid to EMC in the States vs Europe where it gets more attention.

[mactec54]

Thanks all for your comments and recommendations, they have been helpful. I will be using shielded cable I just need to get things running before it arrived. It’s not very elegant but I have my spindle power cable dropping from the ceiling so it is pretty far away from other cables. Anyone have experience with ferrite cores or similar?

On the topic of shielded vs unshielded being proper and per code, what I can say, at least on the large HVAC equipment I work with is many cables are not shielded. EMC is dealt with using other methods such as having the cables in a metal raceway, so I think it’s fair to say that shielded cable isn’t always required but some form of mitigation for EMC is generally needed, whether that is in the form of shielded VFD cable or not. Also I don’t see much attention paid to EMC in the States vs Europe where it gets more attention.

Yes it is quite common practice to use unshielded cable in industrial settings, buy way of conduit or steel race ways or even just twisted wires, the US is the only country I know of that does noncompliant installs, most VFD Drives used in the US industry are EMC compliant so this eliminates most of the noise problems anyway

Just remember the industry is using 3Ph power which is balanced this in it's self creates lower harmonic noise problems, it is very different from unbalanced residential 240v single phase supply, this creates a lot more harmonics in your power system when using a VFD Drive