Danfoss VLT Series Design Manual page 54

2. Introduction to the VLT HVAC Drive
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
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voltage level.
Line Drop-out
During a line drop-out, the adjustable frequency drive keeps running until the intermediate circuit
voltage drops below the minimum stop level, which is typically 15% below the adjustable fre-
quency drive's lowest rated supply voltage.
The line voltage before the drop-out and the motor load determine how long it takes for the
inverter to coast.
Static Overload in VVCplus mode
When the adjustable frequency drive is overloaded (the torque limit in par. 4-16/4-17 is reached),
the control reduces the output frequency to reduce the load.
If the overload is excessive, a current may occur that makes the adjustable frequency drive cut
out after approximately 5-10 s.
Operation within the torque limit is limited in time (0-60 s) in par. 14-25.
2.14.1. Motor Thermal Protection
The motor temperature is calculated on the basis of motor current, output frequency, and time
or thermistor. See par. 1-90 in the Programming Guide.
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MG.11.B4.22 - VLT ® is a registered Danfoss trademark.
VLT ® HVAC Drive Design Guide
Overvoltage Control .