5-8 Power Wiring 3AXD50000011888
5.5.1 Protecting the Motor Insulation and Bearings
The drive employs modern IGBT inverter technology. Regardless of frequency, the drive output comprises pulses of
approximately the drive DC bus voltage with a very short rise time. The pulse voltage can almost double at the motor
terminals, depending on the attenuation and reection properties of the motor cable and the terminals. This can cause
additional stress on the motor and motor cable insulation. Modern variable speed drives with their fast rising voltage pulses
and high switching frequencies can generate current pulses that ow through the motor bearings. This can gradually erode
the bearing races and rolling elements. Optional du/dt lters protect motor insulation system and reduce bearing currents.
Optional common mode lters mainly reduce bearing currents. Insulated N-end (non-drive end) bearings protect the motor
bearings. Cooling tower motors are also available with optional grounding brushes and insulated bearings, which also
reduce bearing currents.
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