Efficiency - Danfoss VLT AutomationDrive FC 300 Design Manual

FC 300 Design Guide

Efficiency

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To reduce energy consumption, it is very important
to optimize the efficiency of a system. The
efficiency of each single element in the system
should be as high as possible.
Efficiency of FC 300 Series (η
The load on the adjustable frequency drive has little effect on its efficiency. In general, the
efficiency is the same at the rated motor frequency f
of the rated shaft torque or only 75%, i.e. partial loads.
This also means that the efficiency of the adjustable frequency drive does not change
even if other U/f characteristics are chosen.
However, the U/f characteristics influence the efficiency of the motor.
There is a slight decline in efficiency when the switching frequency is set to a value above
5 kHz. The rate of efficiency will also be slightly reduced if the mains voltage is 500 V,
or if the motor cable is longer than 100 ft (30 m).
Efficiency of the motor (η
The efficiency of a motor connected to the adjustable frequency drive depends on the sine
shape of the current. In general, the efficiency is just as good as with mains operation. The
efficiency of the motor depends on the type of motor.
In the range of 75-100% of the rated torque, the efficiency of the motor is practically constant, both
when it is controlled by the adjustable frequency drive and when it runs directly on mains.
In small motors, the influence of the U/f characteristic on efficiency is marginal. However, in
motors from 15 HP (11 kW) and up, the advantages are significant.
In general, the switching frequency does not affect the efficiency of small motors. Motors from
15 HP (11 kW) and up have their efficiency improved (1-2%). This is because the sine shape
of the motor current is almost perfect at high switching frequency.
Efficiency of the system (η
To calculate the system efficiency, the efficiency of FC 300 Series (η
by the efficiency of the motor (η
η ) = η x η
SYSTEM VLT MOTOR
Estimate the efficiency of the system at different loads based on the graph above.
How to Select Your VLT
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VLT
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MOTOR
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SYSTEM
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MOTOR
MG.33.B3.22 - VLT is a registered Danfoss trademark
, even if the motor supplies 100%
M,N
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VLT
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