ABB FOCH, Hardware Manual, Page: 9 / 38

Operation principle
Contents of this chapter
This chapter describes the operation principle of the d u/dt filter.
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.
There are optional common mode filters and d u/dt filters available for the ABB drives.
The common mode filters mainly reduce bearing currents. The d u/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 drive
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.
￭
Graphs illustrating the effect of the du/dt filter
The graphs show the peak line-to-line voltage ( Û
LL
) and voltage change (d u/dt) at the
motor terminals as a function of the motor cable length.
Û
LL
and d
u/dt are scaled to
2
Operation principle 9