Planning the electrical installation 61 Protecting the motor insulation and bearingsThe drive employs modern IGBT inverter technology. Regardless of frequency, thedrive output comprises pulses of approximately the drive DC bus voltage with a veryshort rise time. The pulse voltage can almost double at the motor terminals,depending on the attenuation and reflection properties of the motor cable and theterminals. This can cause additional stress on the motor and motor cable insulation.Modern variable speed drives with their fast rising voltage pulses and high switchingfrequencies can generate current pulses that flow through the motor bearings. Thiscan 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 tableThe following table shows how to select the motor insulation system and when anoptional drive du/dt and common mode filters and insulated N-end (non-drive end)motor bearings are required. Ignoring the requirements or improper installation mayshorten motor life or damage the motor bearings and voids the warranty.
