Hardware Manual

Planning the electrical installation 59
 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 reflection 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 flow through the motor bearings. This
can gradually erode the bearing races and rolling elements.
Optional du/dt filters protect motor insulation system and reduce bearing currents.
Optional common mode filters mainly reduce bearing currents. Insulated N-end (non-
drive end) bearings protect the motor bearings.
 Requirements table
The following table shows how to select the motor insulation system and when an
optional drive du/dt and common mode filters and insulated N-end (non-drive end)
motor bearings are required. Ignoring the requirements or improper installation may
shorten motor life or damage the motor bearings and voids the warranty.