Rfi Switch; Direction Of Motor Rotation; Parallel Connection Of Motors - Danfoss VLT 2800 Manual

RFI switch

Mains supply isolated from earth:
If the frequency converter is supplied from an isolated
mains source ( IT mains) or TT/TN-S mains with groun-
ded leg, the RFI switch is recommended to be turned
off (OFF). For further reference, see IEC 364-3. In
case optimum EMC performance is needed, parallel
motors are connected or the motor cable length is
above 25 m, it is recommended to set the switch in ON
position.
In OFF position, the internal RFI capacities (filter ca-
pacitors) between the chassis and the intermediate
circuit are cut off to avoid damage to the intermediate
circuit and to reduce the earth capacity currents (ac-
cording to IEC 61800-3).
Please also refer to the application note VLT on IT
mains, MN.90.CX.02. It is important to use isolation
monitors that are capable for use together with power
electronics (IEC 61557-8).
NB!
The RFI switch is not to be operated with
mains connected to the unit. Check that
the mains supply has been disconnected
before operating the RFI switch.
NB!
The RFI switch disconnects the capaci-
tors galvanically from ground.
The switch Mk9, placed next to terminal 96, should be
removed to disconnect the RFI-filter.
The RFI switch is only available on VLT 2880-2882.
50

Direction of motor rotation

The factory setting is for clockwise rotation with the
frequency converter 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 on the motor terminals.

Parallel connection of motors

The frequency converter is able to control several mo-
tors connected in parallel. If the motors are to have
different rpm values, use motors with different rated
rpm values. Motor rpm is changed simultaneously,
which means that the ratio between the rated rpm val-
ues is maintained across the range. The total current
consumption of the motors is not to exceed the maxi-
mum rated output current I
verter.
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
MG.27.E2.02 - VLT is a registered Danfoss trademark
for the frequency con-
INV