ABB ACS880-17 - Protecting the Motor Insulation and Bearings

70 Guidelines for planning the electrical installation
Select the motor size and drive type from to the rating tables in chapter Technical data on
basis of the AC line voltage and motor load. Use the DriveSize PC tool if you need to tune
the selection more in detail.
Make sure that the motor withstands the maximum peak voltage in the motor terminals.
See the Requirements table on page 71. For basics of protecting the motor insulation and
bearings in drive systems, refer to section Protecting the motor insulation and bearings
below.
Note:
• Consult the motor manufacturer before using a motor whose nominal voltage differs
from the AC line voltage connected to the drive input.
• The voltage peaks at the motor terminals are relative to the supply voltage of the drive,
not the drive output voltage.
• If the motor and drive are not of the same size, consider the following operation limits
of the drive control program:
• motor nominal voltage range 1/6 ... 2 · U
N
• motor nominal current range 1/6 ... 2 · I
N
of the drive in DTC control and 0 ... 2 · I
N
in scalar control. The control mode is selected by a drive parameter.
 Protecting the motor insulation and bearings
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. This can
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.