VLT® 5000 Crane
■
Derating for Ambient Temperature
The ambient temperature (T
AMB,MAX
) is the maximum
temperature allowed. The average (T
AMB,AVG
) is
measured over 24 hours and must be at least 5ºC lower.
NB!:
VLT 5000 Crane is already derated for
operational temperature (55° T
AMB,MAX
and 50° T
AMB,AVG
.
■
Derating for air pressure
Below 1000 m derating is not necessary.
Above 1000 m the ambient temperature (T
AMB
)
or max. output current (I
MAX
) must be derated in
accordance with the diagram below:
1. Derating of output current versus altitude
2. Derating of max. T
AMB
versus altitude at
100% output current.
■
Derating for Running at Low Speed
When a motor is connected to a frequency
converter, it is necessary to check whether the
cooling of the motor is adequate.
At low RPM values, the motor fan is not able to
supply the required volume of air for cooling. This
problem occurs when the load torque is constant
(e.g. a conveyor belt) across the regulating range.
The reduced ventilation available decides the size of
the torque that can be permitted under a continuous
load. If the motor is to run continuously at an RPM
value lower than half the rated value, the motor must
be supplied with additional air for cooling.
Instead of such extra cooling, the load level of
the motor can be reduced. This can be done by
choosing a bigger motor. However, the design of
the frequency converter sets limits as to the size
of motor that can be connected to it.
MG.50.N4.02 - VLT is a registered Danfoss trademark
94
