VFD Power Cable

<...Shielded cable for connecting the motor having a low lineic capacitance if the switching frequency is high, How the cable capacitance affect the motor...>

A non-CE-marked VFD may fall outside radio frequency emissions parameters necessary for CE marking to be valid. For this reason, shielded cables downstream of it have been recommended.

Cable capacitance does not affect the motor but might disturb the VFD.

I suspect that your VFD can be used in a servo operation. So despite the advantage that cable shielding gives to an installation to prevent RFI, I believe you'll find your answer back in feedback basics. Adding the pole of higher cable capacitance to the circuit may have inadvertently made an undamped mechanical oscillator for somebody's installation. It was far easier for the manufacturer to say "don't use a shield" than expecting a technician to parametrize the driver and mechanics so that a proper Routh test analysis could be accomplished.

its not a VFD for Servo motor its for asynchronous motor,3 phase squirrel cage induction motor.

I realize that this is a VFD driving a 3 phase induction motor and not a DC servomotor. My comment is that this motor and drive system maybe configured in a servo or negative feedback control loop. Not all servo loops use servomotors.

This drives name is Altivar 31 manufactured by Telemacanique a brand of Schneider Electric. For an encoder feedback application we user a higher version of this drive called Altivar 71.

1. Supply cable has a high harmonic current content causing extra cable heat, however, if you take the RMS value and usual selection criteria, it may be screened or not. The motor cable is normally recommended as screened to leesen the electromagnetic radiation emanating from motor cables. If this is not important, its not necessary e.g. short cable run not close to other sensitive (vulnerable) equipment / cables. If the switching frequency is high with higher capacitance cable (longer run etc) this can cause a transmission line effect doubling voltage at the motor which potentially can damage the motor insulation causing motor failure. This normally can also cause High current trip on VFD but normally does no harm if corrected.

2. ' Non shielded wires for relay contacts' - maybe this refers to the VFD control circuit where digital I/O are less susceptible to noise than analogues. If there'e noise about, use screened cable for all control wiring to VFD with screen tied down at the source end ONLY. Its quite common to see analogue screened, I/O not screened but VFD manuals normally ask for all screened when directly connected to VFD.