Planning the electrical installation
58
Checking the compatibility of the motor and drive
Use an AC induction motor or a permanent magnet synchronous motor with the
drive. Several induction motors can be connected at a time but only one permanent
magnet motor.
Select the motor and drive according to the rating tables in chapter Technical Data.
Use the DriveSize PC tool if the default load cycles are not applicable.
1. Check that the motor ratings lie within the allowed ranges of the drive control
program:
• motor nominal voltage is in the range of 1/2...2 · U
N
• motor nominal current is 1/6 ... 2 · I
Hd
of the drive in DTC control and
0 ... 2 · I
Hd
in scalar control. The control mode is selected by a drive parameter.
2. Check that the motor voltage rating meets the application requirements:
See note 6 below the Requirements table, page 61.
3. Consult the motor manufacturer before using a motor in a drive system where the
motor nominal voltage differs from the AC power source voltage.
4. Ensure that the motor insulation system withstands the maximum peak voltage in
the motor terminals. See the Requirements table below for the required motor
insulation system and drive filtering.
Example 1: When the supply voltage is 440 V and the drive 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.
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, which
can gradually erode the bearing races and rolling elements.
Optional du/dt filters protect motor insulation system and reduce bearing currents.
Common mode filters mainly reduce bearing currents.
When … the motor voltage rating should be …
No resistor braking is in use U
N
Frequent or long term brake cycles will
be used
1.21
· U
N
U
N
input voltage of the drive
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