Du/Dt Conditions - Danfoss FC 300 Design Manual

4. FC 300 Selection
Typical values are measured at a distance of 3.28 ft. [1 m] from the unit:
FC 301/FC 302
PK25-P7K5: @ 400 V
PK25-P7K5
Reduced fan speed
Full fan speed
When a transistor in the inverter bridge switches, the voltage across the motor in-
4
creases by a du/dt ratio depending on:
-
-
The natural induction causes an overshoot U
a level depending on the voltage in the intermediate circuit. The rise time and the peak voltage
U
PEAK
coil insulation are especially affected. If the motor cable is short (by a few yards), the rise time
and peak voltage are lower.
If the motor cable is long (328 ft. [100 m]), the rise time and peak voltage are higher.
In motors without phase insulation paper or other insulation reinforcement suitable for operation
with voltage supply (such as an adjustable frequency drive), fit a du/dt filter or a sine-wave filter
on the output of the adjustable frequency drive.

4.6.1. du/dt conditions

Peak voltage on the motor terminals is caused by the switching of the IGBTs. The FC300 complies
with the requirements of IEC 60034-25 regarding motors designed to be controlled by adjustable
frequency drives. The FC 300 also complies with IEC 60034-17 regarding norm motors controlled
by adjustable frequency drives.
Measured values from lab tests:
Cable length
5
50
150
1) FC 302 only
82
the motor cable (type, cross-section, length, shielded or unshielded)
inductance
affect the service life of the motor. If the peak voltage is too high, motors without phase
FC 300
2 hp [1.5 kW], 400 V
du/dt
U [V]
peak
V/μ s
690 1329
985 985
1) 1045 947
MG.33.B9.22 - VLT
IP 20/IP 21/NEMA TYPE 1
IP55/NEMA TYPE 12
in the motor voltage before it stabilizes itself at
PEAK
FC 300 FC 300
5 hp [4.0 kW], 400 V 10 hp [7.5 kW], 400 V
du/dt
U [V] U [V]
peak peak
V/μ s
890 4156 739
180 2564 1040
1190 1770 1030
® is a registered Danfoss trademark.
FC 300 Design Guide
51 dB(A)
60 dB(A)
du/dt
V/μ s
8035
4548
2828