132
MG.30.A7.02 - VLT
®
is a registered Danfoss trademark
Derating for air pressure
Below 1000 m altitude no derating is
necessary.
Above 1000 m the ambient temperature
(t
AMB
) or max. output current (I
VLT,MAX
) must
be derated according to the graph below:
1. Derating of output current versus
altitude at t
AMB
= max. 40
°
C.
2. Derating of max. t
AMB
versus altitude
at 100% output current.
Derating
teristic for centrifugal pumps/fans. Motors
running constant load torque applications
at low speed must be derated or force-
cooled (see graph).
Motor derating for running at low speed
When a centrifugal pump or fan is con-
trolled by the VLT
®
Series 3000 it is not
necessary to reduce the output current at
low speed because of the load charac-
Derating for running at low speed
Derating for higher switching frequencies
Applies only to VLT
®
types 3002-52 as the
maximum switching frequency is 4.5 kHz
set in the VLT
®
types 3060-3250.
A higher switching frequency (para. 224)
results in greater loss and stronger heat
formation in the frequency converter’s tran-
sistors and motor coils.
The frequency converter therefore auto-
matically derates the maximum permitted
constant output current I
VLT,N
, when the
switching frequency exceeds 4.5 kHz.
Linear reduction is performed down to 60%
at 14 kHz (see graph).
Derating for higher switching frequencies
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