Motor Bearing Currents - Danfoss VLT AQUA Instruction Manual

VLT AQUA High Power Instruction Manual

3.6.19 Motor Bearing Currents

All motors installed with 150 hp [110 kW] or higher power drives should have NDE (Non-Drive End) insulated bearings installed to eliminate circulating
bearing currents. To minimize DE (Drive End) bearing and shaft currents proper grounding of the drive, motor, driven machine, and motor to the driven
machine is required.
Standard Mitigation Strategies:
1. Use an insulated bearing
2. Apply rigorous installation procedures
- Strictly follow the EMC Installation guideline
- Provide a good high frequency connection between the motor and the adjustable frequency drive for instance by shielded cable which
has a 360° connection in the motor and the adjustable frequency drive.
- Provide a low impedance path from adjustable frequency drive to building ground and from the motor to building ground. This can be
difficult for pumps
- Make a direct ground connection between the motor and load machine
- Reinforce the PE so the high frequency impedance is lower in the PE
- Ensure the motor and load motor are aligned
3. Lower the IGBT switching frequency
4. Modify the inverter waveform, 60° AVM vs. SFAVM
5. Install a shaft grounding system or use an isolating coupling between motor and load
6. Apply conductive lubrication
7. If the application allows, avoid running at low motor speeds by using the minimum speed settings of the drive.
8. Try to ensure the line voltage is balanced to ground. This can be difficult for IT, TT, TN-CS or Grounded leg systems
9. Use a dU/dt or sinus filter
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MG.20.P3.22 - VLT is a registered Danfoss trademark
3 How to Install
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