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Posted By Topic: VSD cable

Mar 18 2020 08:37

Hi All,

I have a number of Teco FM50 VSD's paired with some small motors between 50-80m away. Some VSD's haven't been functioning for many years due to water damage and will be getting replaced. The motor cable originally installed is standard 3c+e tps run with the other installation wiring through multiple tenancy's. I'm concerned due to the lack of proper VSD cable being used that once these are powered up again there will be an impact from interference on some of the other tenancy's. As far as I can see this model VSD recommends shielded cable but was wondering if there is any reason why this may be ok to run as is. To replace the cabling will be a major undertaking due to cable routes and want to be 100% sure it will be required. I suspect that the whole setup was never very well done anyway, with some motors wired from the vsd in star, others in delta, no earthing on the drives, no ventilation etc.. Last thing I want to do is get everything up and running again and find I have created a whole lot of new problems.

Any advise would be appreciated before I make any recommendations.

Mar 18 2020 09:07

Not a nice position to be in, I guess relocating the drives to a place nearer the motors where you can use vsd cable between motor and drive is not an option?

Mar 18 2020 12:35

"3000" 4.12 applies to VFDs.
However on this case you're not installing, just replacing existing fittings [ESR 59(3)]. So no absolute requirement to upgrade provided the original installation was compliant with rules of the time. Which depends on when it was installed; and would take some working through.

But you're right that using TPS was asking for trouble

Mar 18 2020 18:57

4.12 doesn't seem to have anything relevant to EMI?

Fitting output filtering to the drives may be possible.

Depending on the design and requirements, mounting the VFD at the motor and using the TPS for supply might be an option. This would depend on how much control you need. It might also be possible to run the control signals via e.g. industrial ethernet.

Whether the motor should be connected in star or delta is entirely dependant on whether the motor is wound for 230/400 or 400/690, and what the incoming supply voltage is. If the VFDs are all 3~400V in, you would normally expect star for motors about 4kW or less, and delta for motors larger. Check the nameplates as this varies. 230V delta would be reasonable for small motors on single-phase input VFDs.

Mar 19 2020 07:26

We had issues with TPS feeding fans from VSDs 40-50 meters away, mainly induction into other cables. We ended up locating VSDs closer to fans about 10 meters away and installing screened VSD cables from VSDs TO fans. Problem sorted.

Mar 19 2020 08:34

As already mentioned, I'd say the best solution would be either relocate VSD local to the fans, or install a sinusoidal filter on their outputs.

Mar 19 2020 09:35

True 4.12 doesn't specifically cover VFDs; just making the point, because many people don't make the association.
Also there's reference in 5.4.8 that is directly relevant to VFDs; though relating to carrying HF currents rather than EMI.
Both issues may need to be dealt with, and no amount of filtering can improve the generally poor HF conductivity of PECs of cables designed for 50 Hz.

Mar 19 2020 11:55

Thanks all for your advice. Relocating the drives closer to the motors is probably not an option. Motors are up on a couple of 4 story buildings and access not possible without an ewp and alot of hassle. Just for control purposes I think I'll leave them in the switchroom for now. I have emailed Teco to see about filtering for their drives. I think I will probably just err on the side of caution though and just look at getting the cabling replaced as well.