Decentral Solutions
All About FCD
300
■
dU/dt on motor
When a transistor in the inverter is opened, the
voltage across the motor terminals will rise by a
voltage/time ratio (dU/dt) determined by:
-
the motor cable (type, cross-section, induction,
capacity, length and shielded/armoured/un-
shielded/unarmoured)
-
the AC line voltage
Self-induction in the motor cable leads to an overswing
U
PEAK
of the output voltage each time a transistor in
the inverter is opened. After U
PEAK
the output voltage
will stabilize at a level determined by the voltage in the
intermediate circuit. U
PEAK
and dU/dt influence the
lifetime of the motor, especially motors without phase
insulation paper in the coils. If the motor cable is short
(a few feet), the overshoot U
PEAK
is low, while the
dU/dt is high. If the motor cable length is increased,
U
PEAK
is increased, while dU/dt decreases.
■
Switching on the input
The waiting time between switching the electrical
voltage on terminals 91, 92 and 93 must be min.
30 sec. Start up time appr. 2.3 sec.
■
Acoustic noise
The acoustic noise from the variable frequency
drive comes from two sources:
1. DC intermediate circuit coils.
2. Inverter.
Below are the typical values measured at a distance
of 3 ft from the unit at full load:
FCD 303-335 3 x 400 V: 52 dB(A).
MG.90.F2.22 - VLT is a registered Danfoss trademark
181
