Derating For Installing Long Motor Cables Or Cables With Larger Cross-Section; Temperature-Dependent Switch Frequency - Danfoss FC 300 Design Manual

FC 300 Design Guide
ventilation available determines 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 (or use a motor designed for this type of operation).
Instead of such extra cooling, the load level of the motor can be reduced e.g. by choosing a larger
motor. However, the design of the adjustable frequency drive sets a limit to the motor size.
Derating for Installing Long Motor Cables or
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Cables with Larger Cross-Section
The max. cable length for FC 301 is 492 ft. [150 m] non-shielded cable and 164 ft. [50 m] shielded cable,
respective for FC 302 is 984 ft. [300 m] non-shielded and 492 ft. [150 m] shielded cable.
The adjustable frequency drive has been tested using 984 ft. [300 m] non-shielded
cable and 492 ft. [150 m] shielded cable.
The adjustable frequency drive has been designed to work using a motor cable with a rated
cross-section. If a cable with a larger cross-section is used, reduce the output current
by 5% for every step the cross-section is increased.
(Increased cable cross-section leads to increased capacity to ground, and thus
an increased ground leakage current).

Temperature-Dependent Switch Frequency

"
This function ensures the highest possible switch
frequency without causing a thermal overload
of the adjustable frequency drive. The internal
temperature indicates whether the switch frequency
can be based on the load, the ambient temperature,
the supply voltage, or the cable length.
The switch frequency is set in par. 14-01.
FC 300 Selection
MG.33.B6.22 - VLT is a registered Danfoss trademark
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