Protecting The Motor Insulation And Bearings - ABB ACS800 Hardware Manual

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Example 1: When the supply voltage is 440 V and a drive with a diode supply is
operating in motor mode only, the maximum peak voltage in the motor terminals
can be approximated as follows: 440 V · 1.35 · 2 = 1190 V. Check that the motor
insulation system withstands this voltage.
Example 2: When the supply voltage is 440 V and the drive is equipped with an
IGBT supply, the maximum peak voltage in the motor terminals can be
approximated as follows: 440 V · 1.41 · 2 = 1241 V. Check that the motor
insulation system withstands this voltage.

Protecting the motor insulation and bearings

The output of the drive comprises – regardless of output frequency – pulses of
approximately 1.35 times the equivalent mains network voltage with a very short rise
time. 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 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.
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 installed
according 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 according
to the following table. Two types of filters are used individually or in combinations:
• optional du/dt filter (protects motor insulation system and reduces bearing
currents).
• common mode filter (mainly reduces bearing currents).
Planning the electrical installation