du/dt and common mode filtering 169
du/dt and common mode
filtering
Contents of this chapter
This chapter describes how to select du/dt and common mode filtering for the drive
module. The chapter also contains the relevant technical data.
When is du/dt or common mode filtering required?
The output of the drive comprises – regardless of output frequency – pulses of
approximately 1.35 times the equivalent supply voltage with a very short rise time.
This is the case with all drives employing modern IGBT drive technology. The motor
and motor cable insulation may undergo the following situation:
• The voltage of the pulses can be almost double at the motor terminals, depending
on the attenuation and reflection properties of the motor cable and the terminals.
This in turn 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.
Use the,
• optional ABB du/dt filters to avoid stress on motor insulation
• common mode filters to reduce bearing currents.
Note: To avoid damage to the motor bearings, select and install the cables according
to the instructions given in Electrical installation on page 73.
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