Derating for Running at Low Speed
When a motor is connected to an adjustable frequency
drive, 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 con-
veyor 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 addi-
tional air for cooling.
Instead of such extra cooling, the load level of the mo-
tor can be reduced. This can be done by choosing a
bigger motor. However, the design of the adjustable
frequency drive sets limits as to the size of motor that
can be connected to it.
Derating for Installing Long Motor Cables or Ca-
bles with Larger Cross-section
The adjustable frequency drive has been tested using
300 m unscreened cable and 150 m screened 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 to be used, it is
recommended to reduce the output current by 5% for
every step the cross-section is increased.
(Increased cable cross-section leads to increased ca-
pacity to earth, and thus an increased earth leakage
current).
Derating for high switching frequency
A higher switching frequency (to be set in parameter
411) leads to higher losses in the electronics of the
adjustable frequency drive.
If
SFAVM
has been selected in parameter 446, the ad-
justable frequency drive will automatically derate the
rated output current I
VLT,N
when the switching frequen-
cy exceeds 3.0 kHz.
If
60°AVM
is selected, the adjustable frequency drive
will automatically derate when the switching frequency
exceeds 4.5 kHz. In both cases, the reduction is car-
ried out linearly, down to 60% of I
VLT,N
. The table gives
the min., max. and factory-set switching frequencies
for adjustable frequency drive. The switching pattern
can be changed in parameter 446 and the switching
frequency in parameter 411.
SFAVM
60 deg. AVM
Min. [kHz]
Max. [kHz]
Fac. [kHz]
Min. [kHz]
Max. [kHz]
Fac. [kHz]
VLT 5001-5006, 200 V
3.0
5.0
3.0
3.0
10.0
4.5
VLT 5008-5027, 200 V
3.0
10.0
3.0
3.0
14.0
4.5
VLT 5032-5052, 200 V
3.0
4.5
3.0
3.0
4.5
4.5
VLT 5001-5011, 500 V
3.0
5.0
3.0
3.0
10.0
4.5
VLT 5016-5052, 500 V
3.0
10.0
3.0
3.0
14.0
4.5
VLT 5062-5102, 500 V
3.0
4.5
3.0
3.0
4.5
4.5
VLT 5122-5302, 500 V
3.0
8.0
3.0
2.0
10.0
4.5
VLT 5352-5552, 600 V
1.5
2.0
2.0
1.5
3.0
3.0
VLT 5001-5011, 600 V
3.0
5.0
3.0
4.5
7.0
4.5
VLT 5016-5027, 600 V
3.0
10.0
3.0
3.0
14.0
4.5
VLT 5032-5052, 600 V
3.0
7.0
3.0
3.0
10.0
4.5
VLT 5062, 600 V
3.0
4.5
3.0
3.0
4.5
4.5
VLT 5042-5302, 690 V
1.5
2.0
2.0
1.5
3.0
3.0
VLT 5352-5602, 690 V
1.5
1.5
1.5
1.5
2.0
2.0
VLT
®
5000 Series
MG.51.C5.22 - VLT
p
is a registered Danfoss trademark.
213
List of functions
Summary of Contents for VLT 5000 Series
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