Danfoss VLT AutomationDrive FC 300 Series - Du;Dt Conditions; Special Conditions; Derating for Ambient Temperature, Frame Size a

4.5 dU/dt Conditions
To avoid damage to motors without phase insulation
paper or other insulation reinforcement designed for
frequency converter operation, it is strongly recommend to
install a dU/dt filter or LC filter on the output of the
converter.
When a transistor in the inverter bridge switches, the
voltage across the motor increases by a dU/dt ratio
depending on:
•
Motor inductance
•
Motor cable (type, cross-section, length, screened
or unscreened)
The natural induction causes an overshoot voltage peak in
the motor voltage before it stabilises. The level depends
on the voltage in the intermediate circuit.
Peak voltage on the motor terminals is caused by the
switching of the IGBTs. The rise time and the peak voltage
affect the service life of the motor. If the peak voltage is
too high, motors without phase coil insulation can be
adversely affected over time.
With short motor cables (a few metres), the rise time and
peak voltage are lower. The rise time and peak voltage
increase with cable length (100 m).
The FC frequency converter complies with IEC 60034-25
and IEC 60034-17 for motor design.
4.6
Special Conditions
This section provides detailed data regarding the operating
of the frequency converter in conditions the require
derating. In some conditions, derating must be done
manually. In other conditions, the frequency converter
performs a degree of automatic derating when necessary.
This is done to ensure proper performance at critical
stages where the alternative could be a trip.
4.6.1
Manual Derating
Consider derating when any of the following conditions
are present.
•
Operating above 1000 m (low air pressure)
•
Low speed operation
•
Long motor cables
•
Cables with a large cross section
•
High ambient temperature
4.6.2 Derating for Ambient Temperature,
Frame Size A
60° AVM - Pulse Width Modulation
2
20%
4 6 8 10 12 14 16
40%
60%
80%
100%
110%
I
out
(%)
f
sw
(kHz)
A1-A3 45°C, A5 40°C
A1-A3 50°C, A5 45°C
A1-A3 55°C, A5 50°C
130BA393.10
0
0
Illustration 4.3 Derating of I
out
for different T
AMB, MAX
for frame
size A, using 60° AVM
SFAVM - Stator Frequency Asyncron Vector Modulation
2
20%
4 6 8 10 12 14 16
40%
60%
80%
100%
110%
f
sw
(kHz)
A1-A3 45°C, A5 40°C
A1-A3 50°C, A5 45°C
A1-A3 55°C, A5 50°C
0
0
130BA395.10
I
out
(%)
Illustration 4.4 Derating of I
out
for different T
AMB, MAX
for frame
size A, using SFAVM
When using only 10 m motor cable or less in frame size A,
less derating is necessary. This is due to the fact that the
length of the motor cable has a relatively high impact on
the recommended derating.
60° AVM
2
20%
4 6 8 10 12 14 16
40%
60%
80%
100%
110%
I
out
(%)
f
sw
(kHz)
A1-A3 45°C, A5 40°C
A1-A3 50°C, A5 45°C
A1-A3 55°C, A5 50°C
0
0
130BA394.10
Illustration 4.5 Derating of I
out
for different T
AMB, MAX
for frame
size A, using 60° AVM and maximum 10 m motor cable
FC 300 Selection
VLT
®
AutomationDrive FC 300 Design Guide, 0.25-75 kW
MG33BE02 - VLT
®
is a registered Danfoss trademark 79
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