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.
3.9.3. Motor Thermal Protection
The electronic thermal relay in the frequency converter has received the UL-approval for single
motor protection, when par. 1-90
Motor Thermal Protection
is set for
ETR Trip
and par. 1-24
Motor
current, I
M,N
is set to the rated motor current (see motor name plate).
For thermal motor protection it is also possible to use the MCB 112 PTC Thermistor Card option.
This card provides ATEX certificate to protect motors in explosion hazardous areas, Zone 1/21 and
Zone 2/22. Please refer to the
Design Guide
for further information.
3. How to Install
VLT
®
Automation Drive FC 300
Operating Instructions High Power
70
MG.33.U1.02 - VLT
®
is a registered Danfoss trademark
3