Extreme Running Conditions - Danfoss VLT 8000 AQUA series Operating Instructions Manual

Extreme running conditions

Short circuit
VLT 8000 AQUA 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 frequency converter will display
a fault code, although depending on impedance
and motor frequency.
Earth fault
The inverter cuts out within 100 ms in case of an
earth 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
frequency converter is fully permitted. It is not possible
to damage VLT 8000 AQUA 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 frequency converter), 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 frequency converter,
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.
Mains drop-out
During a mains drop-out, VLT 8000 AQUA continues
until the intermediate circuit voltage drops below the
minimum stop level, which is typically 15% below VLT
8000 AQUA's lowest rated supply voltage.
The time before the inverter stops depends on the mains
voltage before the drop-out and on the motor load.
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VLT 8000 AQUA
Static overload
When VLT 8000 AQUA is overloaded (the current
limit in parameter 215 Current limit, I
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 frequency converter 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
MG.83.A2.02 - VLT is a registered Danfoss trademark
has been
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