Danfoss VLT Series Design Manual page 113

VLT ® HVAC Drive Design Guide
5.4.5. Parallel Connection of Motors
The adjustable frequency drive can control
several parallel-connected motors. The total
current consumption of the motors must not
exceed the rated output current I
adjustable frequency drive.
Problems may arise at start and at low RPM
values if motor sizes are widely different, be-
cause small motors' relatively high ohmic re-
sistance in the stator calls for a higher voltage
at start and at low RPM values.
The electronic thermal relay (ETR) of the ad-
justable frequency drive cannot be used as
motor protection for the individual motor of
systems with parallel-connected motors. Pro-
vide further motor protection with, for exam-
ple, thermistors in each motor or individual
thermal relays (circuit breakers are not a suit-
able means of protection).
for the
INV
NOTE
When motors are connected in
Automatic
parallel, par. 1-02
Motor Adaptation (AMA)
cannot
be used.
MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
5. How to Install
5
113