VLT
®
6000 HVAC
63
MG.60.B1.02 - VLT is a registered Danfoss trade mark
Installation
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Motor cables
See
Technical data
for correct sizing of motor cable
cross-section and length.
Always comply with national and local regulations on
cable cross-sections.
NB!
If an unscreened/unarmoured cable is used,
some EMC requirements are not complied
with, see
EMC test results
.
If the EMC specifications regarding emission are to be
complied with, the motor cable must be screened/
armoured, 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 VLT frequency converters.
Mounting 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.
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Parallel coupling of motors
VLT 6000 HVAC is able to control several motors
connected in parallel. If the motors are to have diffe-
rent 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 VLT frequency converter.
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Direction of motor rotation
The factory setting is for clockwise rotation with the
VLT 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 rotation can be changed by switching
two phases in the motor cable.
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.
In systems with motors connected in parallel, the
electronic thermal relay (ETR) of the VLT frequency
converter cannot be used as motor protection for the
individual motor. Consequently, additional motor
protection is required, such as thermistors in each
motor (or individual thermal relays).
NB!
Parameter 107
Automatic Motor Adaptation,
AMA
and
Automatic Energy Optimization, AEO
in parameter 101
Torque characteristics
cannot be
used if motors are connected in parallel.