Danfoss VLT 6000 HVAC Series User Manual

Extreme running conditions
Short circuit
VLT 6000 HVAC is protected against short circuits by
means of current measurement in each of the three
motor phases. A short circuit between two output pha-
ses will cause an overcurrent in the inverter. However,
each transistor of the inverter will be turned off indi-
vidually when the short circuit current exceeds the
permitted value.
After a few microseconds 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 a few micorseconds in
case of an earth fault on a motor phase, although de-
pending 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 6000 HVAC 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 mo-
ment 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 con-
verter, the motor and the installation.
The control unit attempts to correct the ramp if possi-
ble.
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 6000 HVAC continues
until the intermediate circuit voltage drops below the
minimum stop level, which is typically 15% below VLT
6000 HVAC'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.
Static overload
When VLT 6000 HVAC is overloaded (the current limit
in parameter 215 Current limit, I
LIM
has been reached),
the controls will reduce the output frequency in an at-
tempt 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
LIM
.
VLT
®
6000 HVAC Series
196 MG.61.B5.02 - VLT
®
is a registered Danfoss trademark

Danfoss VLT 6000 HVAC Series Specifications

General

Brand	Danfoss
Model	VLT 6000 HVAC Series
Category	DC Drives
Language	English