Danfoss VLT 5000 Series Instruction Manual page 220

Efficiency
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 VLT 5000 Series (
The load on the frequency converter has little effect on
its efficiency. In general, the efficiency is the same at
the rated motor frequency f
M,N
the motor supplies 100% of the rated shaft torque or
only 75%, i.e. in case of part loads.
This also means that the efficieny of the frequency
converter does not change even if other U/f charac-
teristics are chosen.
However, the U/f characteristics influence the efficien-
cy of the motor.
Efficiency of the motor (
MOTOR
The efficiency of a motor connected to the frequency
converter 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 effi-
ciency of the motor is practically constant, both when
it is controlled by the frequency converter and when it
runs directly on mains.
In small motors, the influence from the U/f character-
istic on efficiency is marginal; however, in motors from
11 kW and up, the advantages are significant.
In general, the switching frequency does not affect the
efficiency of small motors. Motors from 11 kW and up
have their efficiency improved (1-2%). This is because
MG.51.C5.22 - VLT is a registered Danfoss trademark.
The efficiency declines a little when the switching fre-
)
VLT
quency is set to a value of above 4 kHz (3 kHz for VLT
5005) (parameter 411). The rate of efficiency will also
be slightly reduced if the mains voltage is 500 V, or if
, regardless of whether
the motor cable is longer than 30 m.
the sine shape of the motor current is almost perfect
)
at high switching frequency.
®
VLT 5000 Series
217