Motor Bearing Currents - GE AF-600 FP Design And Installation Manual

Installation Consideration

7.7 Motor Bearing Currents

All motors installed with 150 hp 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
- Ensure the motor and load motor are
aligned
- Strictly follow the EMC Installation
guideline
- Reinforce the PE so the high frequency
impedance is lower in the PE than the
input power leads.
- 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
- Make sure that the impedance from
adjustable frequency drive to building
ground is lower that the grounding
impedance of the machine. This can be
difficult for pumps.
- Make a direct ground connection
between the motor and load motor.
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.
6. Apply conductive lubrication
7. Use minimum speed settings, if possible.
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
AF-600 FP Design and Installation Guide
DET-768A
7 7
7-9