EN / ACS800-31/U31 Hardware Manual - Simark Controls

41Protecting the motor insulation and bearingsThe output of the drive comprises – regardless of output frequency – pulses ofapproximately 1.35 times the equivalent mains network voltage with a very short risetime. This is the case with all drives employing modern IGBT inverter technology.The voltage of the pulses can be almost double at the motor terminals, depending onthe attenuation and reflection properties of the motor cable and the terminals. This inturn 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, whichcan gradually erode the bearing races and rolling elements.The stress on motor insulation can be avoided by using optional ABB du/dt filters.du/dt filters also reduce bearing currents.To avoid damage to motor bearings, the cables must be selected and installedaccording to the instructions given in the hardware manual. In addition, insulated N-end (non-driven end) bearings and output filters from ABB must be used accordingto the following table. Two types of filters are used individually or in combinations:• optional du/dt filter (protects motor insulation system and reduces bearingcurrents).• common mode filter (mainly reduces bearing currents).Planning the electrical installation