Motor Thermal Protection - Danfoss vlt fc 300 Instruction Manual

VLT
How to Install
Instruction Manual High Power
3.7.2 Parallel Connection of Motors
The adjustable frequency drive can control several motors
connected in parallel. The total current consumption of the
3 3
motors must not exceed the rated output current I
the adjustable frequency drive.
NOTE!
Installations with cables connected in a common joint as in
Figure 3.48, is only recommended for short cable lengths.
NOTE!
When motors are connected in parallel, 1-29 Automatic
Motor Adaptation (AMA) cannot be used.
NOTE!
The electronic thermal relay (ETR) of the adjustable
frequency drive cannot be used as motor protection for
the individual motor of systems with motors connected in
parallel. Provide further motor protection with, for
example, thermistors in each motor or individual thermal
relays (circuit breakers are not suitable for protection).
3-48 MG34Q222 - VLT
Remote Site Products - 1-888-532-2706 - www.remotesiteproducts.com
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®
Automation Drive FC 300 12-Pulse
for
M,N
LC lter
Figure 3.48
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.

3.7.3 Motor Thermal Protection

The electronic thermal relay in the adjustable frequency
drive has received UL-approval for single motor protection,
when 1-90 Motor Thermal Protectionis set for ETR Trip and
1-24 Motor Current is set to the rated motor current (see
motor nameplate).
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. When 1-90 Motor Thermal
Protection is set to [20] ATEX ETR is combined with the use
of MCB 112, it is possible to control an Ex-e motor in
explosion hazardous areas. Consult the programming
guide for details on how to set up the drive for safe
operation of Ex-e motors.
® is a registered Danfoss trademark