Operation principle
7
Operation principle
What this chapter contains
The chapter describes the operation of the du/dt filter and the intended use.
Operation principle
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, which
can gradually erode the bearing races and rolling elements.
The common mode filters mainly reduce bearing currents. The du/dt filters also
protect the motor insulation system.
To avoid damage to motor bearings and insulation system:
• Select and install the cables according to the instructions given in the hardware
manual.
• Check if the installation needs to be equipped with additional protection
equipment, such as insulated N-end bearings in the motor, or the drive output
filters. The requirements are specified in the drive Hardware manual. See chapter
Planning the electrical installation, section Selecting the motor, and chapter du/dt
filter.
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