Danfoss VLT 5005 Design Guide

Extreme Running Conditions
Short circuit
The frequency converter is protected against short cir-
cuits 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. How-
ever, each transistor of the inverter will be turned off
individually when the short circuit current exceeds the
permitted value.
After 5-10 s the driver card turns off the inverter and
the frequency converter will display a fault code, al-
though depending on impedance and motor frequen-
cy.
Earth fault
The inverter cuts out within a few s in case of an earth
fault on a motor phase, although depending on impe-
dance 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 5000 Series 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), ie.
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 requency 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, the frequency converter con-
tinues until the intermediate circuit voltage drops be-
low the minimum stop level, which is typically 15%
below the frequency converter'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 the frequency converter is overloaded (the tor-
que limit in parameter 221/222 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 frequency converter cut out after approx.
1.5 sec.
Operation within the torque limit can be limited in time
(0-60 s) in parameter 409.
VLT
®
5000 Design Guide
MG.52.B2.02 - VLT
®
is a registered Danfoss trademark 111
Special conditions

Danfoss VLT 5005 Specifications

General

Brand	Danfoss
Model	VLT 5005
Category	DC Drives
Language	English