Motor Thermal Protection - Danfoss VLT Automation Drive FC 300 Instruction Manual

3 How to Install
3.10.2 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
NOTE!
Installation with cables connected in a common joint,
3
as in the illustration below, is only recommended for
short cable lengths.
NOTE!
When motors are connected in parallel, par. 1-29
tomatic Motor Adaptation (AMA)
NOTE!
The electronic thermal relay (ETR) of the adjustable
frequency drive cannot be used as motor protection for
the individual motor of systems with parallel-connec-
ted motors. Provide further motor protection with, for
example, thermistors in each motor or individual ther-
mal relays (circuit breakers are not suitable for pro-
tection).
Problems may arise at start and at low RPM values if motor sizes are widely different because small motors' relatively high ohmic resistance in the stator
calls for a higher voltage at start and at low RPM values.

3.10.3 Motor Thermal Protection

The electronic thermal relay in the adjustable frequency drive has received UL approval for single motor protection when par. 1-90
Protection is set for ETR Trip
For thermal motor protection, it is also possible to use the MCB 112 PTC thermistor card option. This card provides an ATEX certificate to protect motors
in explosion hazard areas, Zone 1/21 and Zone 2/22. Please refer to the
3-64
for the adjustable frequency drive.
M,N
cannot be used.
and par. 1-24 Motor current, I
M,N
MG.33.U2.22 - VLT
Au-
is set to the rated motor current (see motor nameplate).
Design Guide for further information.
® is a registered Danfoss trademark
VLT ® Automation Drive FC 300
Instruction Manual High Power
Motor Thermal