FC 300 Design Guide
How to S elect Your VLT
" Peak Voltage on Motor
When a transistor in the adjustable frequency drive is opened, the voltage across the
motor increases by a dV/dt ratio depending on:
- the motor cable (type, cross-section, length shielded or non-shielded)
- inductance
The natural induction causes an overshot U
PEAK
in the motor voltage before it stabilizes itself at a level
depending on the voltage in the intermediate circuit. The rise time and the pe ak voltage U
PEAK
affect the
service life of the motor. If the peak voltage i
s too high, motors without phase coil insulation in particular
are affected. If the motor cable is short (a few meters), the rise time and peak voltage are lower.
Ifthemotorcableislong(300ft/100m),therisetimeandpeakvoltageincrease.
If very small motors are used without phase coil insulation, connect an LC fil-
ter to the adjustable frequency drive.
61
MG.33.B3.22 - VLT is a registered Danfoss trademark
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