Danfoss VLT AutomationDrive FC 300 Design Manual page 49

FC 300 Design Guide
Short Circuit (Motor Phase – Phase)
The frequency converter is protected against short circuits by means of current measurement in
each of the three motor phases or in the DC link. A short circuit between two output phases will
cause an overcurrent in the inverter. The inverter will be turned off individually when the short
circuit current exceeds the permitted value (Alarm 16 Trip Lock.
To protect the drive against a short circuit at the load sharing and brake outputs please see the
design guidelines.
Switching on the Output
Switching on the output between the motor and the frequency converter is fully permitted. You
cannot damage the frequency converter in any way by switching on the output. However, fault
messages may appear.
Motor-generated Overvoltage
The voltage in the intermediate circuit is increased when the motor acts as a generator. This occurs
in following cases:
1.
2.
3.
The control unit may attempt to correct the ramp if possible (par. 2-17
The inverter turns off to protect the transistors and the intermediate circuit capacitors when a
certain voltage level is reached.
See par. 2-10 and par. 2-17 to select the method used for controlling the intermediate circuit
voltage level.
Mains Drop-out
During a mains drop-out, the frequency converter keeps running until the intermediate circuit
voltage drops below the minimum stop level, which is typically 15% below the frequency conver-
ter's lowest rated supply voltage.
The mains voltage before the drop-out and the motor load determines how long it takes for the
inverter to coast.
Static Overload in VVCplus mode
When the frequency converter is overloaded (the torque limit in par. 4-16/4-17 is reached), the
controls reduces the output frequency to reduce the load.
The load drives the motor (at constant output frequency from the frequency converter),
ie. the load generates energy.
During deceleration ("ramp-down") if the moment of inertia is high, the friction is low
and the ramp-down time is too short for the energy to be dissipated as a loss in the
frequency converter, the motor and the installation.
In-correct slip compensation setting may cause higher DC link voltage.
MG.33.B9.02 - VLT ® is a registered Danfoss trademark
3. Introduction to FC 300
Over-voltage Control
.
3
49