VLT
®
5000 Series
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.
When frequency converters are used together with
LC filters to reduce the acoustic noise from a motor,
the switching frequency must be set according to
the LC filter instruction in Parameter 411. When
setting the switching frequency higher than 3 kHz,
the output current is derated in SFAVM mode. By
changing Parameter 446 to 60° AVM mode, the
frequency at which the current is derated is moved
upwards. Please see Design Guide.
■ Connection of motor
All types of 3-phased asynchronous standard motors
can be used with the VLT 5000 Series.
Normally, small motors are star-connected
(200/400 V,
/Y).
Large motors are delta-connected (400/690 V,
/Y).
■ 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.
■ 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
VLT,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.51.A9.02 - VLT is a registered Danfoss trademark
44
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