VLT
®
4000 VT
All about VLT 4000
VT
■
Extreme running conditions
Short circuit
VLT 4000 VT is protected against short circuits
by means of current measurement in each of the
three motor phases. A short circuit between two
output phases will cause an overcurrent in the
inverter. However, each transistor of the inverter
will be turned off individually when the short circuit
current exceeds the permitted value.
After 5-10 ms the driver card turns off the inverter and
the AFD will display a fault code, although depending
on impedance and motor frequency.
Ground fault
The inverter cuts out within 100 ms in case of an
ground fault on a motor phase, although depending
on impedance and motor frequency.
Switching on the output
Switching on the output between the motor and the
AFD is fully permitted. It is not possible to damage
VLT 4000 VT 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 two cases:
1. The load drives the motor (at constant
output frequency from the AFD), i.e. the
load generates energy.
2. During deceleration ("ramp-down") if the moment of
inertia is high, the load is low and the ramp-down
time is too short for the energy to be dissipated as a
loss in the VLT AFD, the motor and the installation.
The control unit attempts to correct the ramp if
possible. The inverter turns off to protect the
transistors and the intermediate circuit capacitors
when a certain voltage level is reached.
Line drop-out
During a line drop-out, VLT 4000 VT continues until
the intermediate circuit voltage drops below the
minimum stop level, which is typically 15% below
VLT 4000 VT
’
s lowest rated supply voltage.
The time before the inverter stops depends on the line
voltage before the drop-out and on the motor load.
Static overload
When VLT 4000 VT is overloaded (the current
limit in parameter 215
Current limit, I
LIM
has been
reached), the controls will reduce the output frequency
in an attempt to reduce the load.
If the overload is excessive, a current may occur that
makes the VLT AFD cut out after approx. 1.5 sec.
Operation within the current limit can be limited in time
(0- 60 s) in parameter 412
Trip delay overcurrent, I
LIM
.
MG.40.A7.22 - VLT is a registered Danfoss trademark
125