AKD 5000
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Electrical installation - motor cables
NB!:
If an unscreened cable is used, some
EMC requirements are not complied with,
see the Design Guide.
If the EMC specifications regarding emission are
to be complied with, the motor cable must be
screened, unless otherwise stated for the RFI filter
in question. It is important to keep the motor cable
as short as possible so as to reduce the noise level
and leakage currents to a minimum.
The motor cable screen must be connected to the
metal cabinet of the frequency converter and to the
metal cabinet of the motor. The screen connections
are to be made with the biggest possible surface
(cable clamp). This is enabled by different installation
devices in the different frequency converters.
Installation with twisted screen ends (pigtails) is
to be avoided, since these spoil the screening
effect at higher frequencies.
If it is necessary to break the screen to install a motor
isolator or motor contactor, the screen must be
continued at the lowest possible HF impedance.
The frequency converter has been tested with a given
length of cable and a given cross-section of that cable.
If the cross-section is increased, the cable capacitance
- and thus the leakage current - increases, and the
cable length must be reduced correspondingly.
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Connection of motor
All types of 3-phased asynchronous standard motors
can be used with the AKD 5000 Series.
Normally, small motors are star-connected
(200/400 V,
/Y).
Large motors are delta-connected (400/690 V,
/Y).
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Direction of motor rotation
The factory setting is for clockwise rotation with the
frequency transformer output connected as follows.
Terminal 96 connected to U-phase
Terminal 97 connected to V-phase
Terminal 98 connected to W-phase
The direction of motor rotation can be changed by
switching two phases in the motor cable.
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Parallel coupling of motors
Frequency converters are able to control several
motors connected in parallel. If the motors are to
have different rpm values, the motors must have
different rated rpm values. Motor rpm is changed
simultaneously, which means that the ratio between
the rated rpm values is maintained across the range.
The total current consumption of the motors is
not to exceed the maximum rated output current
I
N
for the frequency converter.
Problems may arise at the start and at low rpm values if
the motor sizes are widely different. This is because the
relatively high ohmic resistance in small motors calls for
a higher voltage at the start and at low rpm values.
MG.50.R3.02 -
38
