4.7.1 Acoustic NoiseThe acoustic noise from the adjustable frequency drive comes from three sources:1. DC intermediate circuit coils.2. Integrated fan.3. RFI filter choke.Typical values are measured at a distance of 3.28 ft. [1 m] from the unit:Frame size At reduced fan speed (50%) [dBA] *** Full fan speed [dBA]A1 51 60A2 51 60A3 51 60A5 54 63B1 61 67B2 58 70C1 52 62C2 55 65D1+D3 74 76D2+D4 73 74E1/E2 * 73 74E1/E2 ** 82 83F1/F2/F3/F4 78 80* 350–675 hp [250 kW], 380–500 V AC and hp 500–550 hp [355–400 kW], 525–690 V AC only** Remaining E1+E2 power sizes.*** For D and E sizes, reduced fan speed is at 87%.4.8.1 du/dt ConditionsNOTE!380–690 VTo avoid premature ageing of motors (without phase insulation paper or other insulation reinforcement) not designed for adjustablefrequency drive operation, Danfoss strongly recommends fitting a du/dt filter or a sine-wave filter on the output of the adjustablefrequency drive. For further information about du/dt and sine-wave filters, see the Output Filters Design Guide - MG90NYXX.When a transistor in the inverter bridge switches, the voltage across the motor increases by a du/dt ratio depending on:- the motor cable (type, cross-section, length, shielded or unshielded)- inductanceThe natural induction causes an overshoot UPEAK in the motor voltage before it stabilizes itself at a level depending on the voltage in the intermediatecircuit. The rise time and the peak voltage U PEAK affect the service life of the motor. If the peak voltage is too high, motors without phase coil insulationare especially affected. If the motor cable is short (by a few yards), the rise time and peak voltage are lower.If the motor cable is long (328 ft. [100 m]), the rise time and peak voltage are higher.Peak voltage on the motor terminals is caused by the switching of the IGBTs. The AutomationDrive FC 300 complies with the demands of IEC 60034-25regarding motors designed to be controlled by adjustable frequency drives. The AutomationDrive FC 300 also complies with IEC 60034-17 regarding normmotors controlled by adjustable frequency drives.Measured values from lab tests:AutomationDrive FC 300, P5K5T2Cablelength [m]AC linevoltage [V]Rise time[μsec]Upeak[kV]du/dt[kV/μsec]5 240 0.13 0.510 3.09050 240 0.23 2.034100 240 0.54 0.580 0.865150 240 0.66 0.560 0.6744 AutomationDrive FC 300 Selection FC 300 Design Guide4-26 MG.33.BC.22 - VLT® is a registered Danfoss trademark4
