Danfoss VLT FC 100 Operating Instructions Manual

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Contents

Danfoss VLT FC 100 Operating Instructions Manual Manual pdf 72 page image

4.1.19 Motor Bearing CurrentsIt is generally recommended that motors of a rating 110kW or higheroperating via Variable Frequency Drives should have NDE (Non-DriveEnd) insulated bearings installed to eliminate circulating bearing cur-rents due to the physical size of the motor. To minimize DE (Drive End)bearing and shaft currents proper grounding of the drive, motor, drivenmachine, and motor to the driven machine is required. Although failuredue to bearing currents is low and very dependent on many differentitems, for security of operation the following are mitigation strategieswhich can be implemented.Standard Mitigation Strategies:1. Use an insulated bearing2. Apply rigorous installation proceduresEnsure the motor and load motor are alignedStrictly follow the EMC Installation guidelineReinforce the PE so the high frequency impedance is lower inthe PE than the input power leadsProvide a good high frequency connection between the motorand the frequency converter for instance by screened cablewhich has a 360° connection in the motor and the frequencyconverterMake sure that the impedance from frequency converter tobuilding ground is lower that the grounding impedance of themachine. This can be difficult for pumps- Make a direct earthconnection between the motor and load motor.3. Apply conductive lubrication4. Try to ensure the line voltage is balanced to ground. This canbe difficult for IT, TT, TN-CS or Grounded leg systems5. Use an insulated bearing as recommended by the motor man-ufacturer (note: Motors from reputable manufacturers will typ-ically have these fitted as standard in motors of this size)If found to be necessary and after consultation with Danfoss:6. Lower the IGBT switching frequency7. Modify the inverter waveform, 60° AVM vs. SFAVM8. Install a shaft grounding system or use an isolating couplingbetween motor and load9. Use minimum speed settings if possible10. Use a dU/dt or sinus filter4.1.20 Control Cable RoutingTie down all control wires to the designated control cable routing asshown in the picture. Remember to connect the shields in a proper wayto ensure optimum electrical immunity.Fieldbus connectionConnections are made to the relevant options on the control card. Fordetails see the relevant fieldbus instruction. The cable must be placedin the provided path inside the frequency converter and tied down to-gether with other control wires (see illustrations).176FA246.10U/T1 96-DC 88R/L1 91 S/L2 92 T/L3 93+DC 89V/T2 97 W/13Illustration 4.16: Control card wiring path for the D3. Con-trol card wiring for the D1, D2, D4, E1 and E2 use thesame path.VLT HVAC Drive High Power Operating In-structions 4 Electrical InstallationMG.11.F3.02 - VLT® is a registered Danfoss trademark 714