Danfoss VT2800 Series User Manual

VLT
®
2800 Series
Problems may arise at the start and at low rpm
values if the motor sizes are widely different. This
is because the small motors’ relatively high ohmic
resistance in the stator ca lls 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 frequency
converter cannot be used as motor protection
for the individual motor. For this reason further
motor protection must be used, e.g. thermistors in
each motor or an individual the rmal relay. (Circuit
breakers are not suitable as protection).
NB!:
Parameter 107 Automatic m otor adaption, AMT
cannot be used when motors are connected
in parallel. Parameter 101 Torque characteristic
must be set to Special motor characteristics [8]
when motors are connected in parallel.
■ Motor cables
See Technical data for correct dimensioning of motor
cable cross-section and length. Always comply with
national and local regulations on cable cross-section.
NB!:
If an unscreened/unarmoured cable is used,
some EMC requirements are not complied with,
see EMC test results in the Design Guide.
If the EMC specificat ions 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 connect ions are to be made
with the biggest possible surface area (cable clamp) .
This is enabled b y different installation devices in
different frequency converters. Mount ing with twisted
screen ends (pigtails) is to be avoided, since these
spoil the screening effect at high frequencies. If it
is necessary to break the screen to install a motor
isolator or motor relay, the screen must be continued
at the lowest possible HF impe da nce.
■ Motor thermal protection
The electronic thermal relay in U L-approved frequency
converters has received the UL-approval for single
motor protection, when pa rame ter 128 Motor thermal
protection has been set for ETR Trip and parameter
105 Motor current, I
M, N
has been programmed to
the rated motor current (see motor nameplate).
■ Brake connection
No. 81 82 Brake resistor
R- R+ terminals
The connection cable to the brake resistor must
be screened/armoured. Connect the screen to the
metal cabinet of the frequency c
onverter and to the
metal cabinet of the brake resistor by means of
cable clamps. Dimension the cross-section of the
brake cable to match the bra
ke torq ue.
See the Design Guide fo
r dimensioning
of brake resistors.
NB!:
Please note that voltages up to 850 V
DC occur on the te
rminals.
■ Earth connection
As leak current to the earth is higher than 3.5 mA, the
frequency conve
rter must always be earthed according
to prevailing national and local regulations. To
guarantee that the earth cable has a good mechanic al
connection
to terminal 95, the cable cross section
must be at least 10 mm
2
or 2 rated earth wires
that are terminated separately. To increa se safety
you can i
nstall a n RCD (Residual Current Device),
which guarantees that the frequency converter trips
when leak current becomes too high. See also
RCD A
pplication Note MN.90.GX.02.
MG.28.E9.02 - VLT is a registered Danfoss trademark
52

Danfoss VT2800 Series Specifications

General

Brand	Danfoss
Model	VT2800 Series
Category	Controller
Language	English