Danfoss VLT Design Guide

8.5 Special Conditions
8.5.1 Purpose of Derating
Take derating into account when using the at low air
pressure (heights), at low speeds, with long motor cables,
cables with a large cross section or at high ambient
temperature. The required action is described in this
section.
8.5.2 Derating for Ambient Temperature
90% output current can be maintained up to max. 50 °C
ambient temperature.
With a typical full load current of EFF 2 motors, full output
shaft power can be maintained up to 50 °C.
For more specific data and/or derating information for
other motors or conditions, please contact Danfoss.
8.5.3 Automatic Adaptations to Ensure
Performance
The constantly checks for critical levels of internal
temperature, load current, high voltage on the
intermediate circuit and low motor speeds. As a response
to a critical level, the can adjust the switching frequency
and / or change the switching pattern in order to ensure
the performance of the . The capability to automatically
reduce the output current extends the acceptable
operating conditions even further.
8.5.4 Derating for Low Air Pressure
The cooling capability of air is decreased at lower air
pressure.
Below 1000m altitude no derating is necessary but above
1000m the ambient temperature (T
AMB
) or max. output
current (I
out
) should be derated in accordance with the
shown diagram.
Illustration 8.3 Derating of output current versus altitude at T
AMB,
MAX
for frame sizes A, B and C. At altitudes above 2km, please
contact Danfoss regarding PELV.
An alternative is to lower the ambient temperature at high
altitudes and thereby ensure 100% output current at high
altitudes. As an example of how to read the graph, the
situation at 2 km is elaborated. At a temperature of 45° C
(T
AMB, MAX
- 3.3 K), 91% of the rated output current is
available. At a temperature of 41.7° C, 100% of the rated
output current is available.
Illustration 8.4
Illustration 8.5
Derating of output current versus altitude at T
AMB, MAX
for
frame size D.
General Specifications and ...
VLT
®
Refrigeration Drive Design Guide
122 MG16G102 - VLT
®
is a registered Danfoss trademark
8
8

Danfoss VLT Specifications

General

Frequency	50/60 Hz
Enclosure	IP20, IP21, IP55, IP66
Series	VLT
Control Technique	Flux Vector Control
Output Voltage	0-Vinput
Control Method	Fieldbus
Communication Interface	PROFIBUS, CANopen
Protection Features	Overload, Overvoltage, Undervoltage, Short Circuit, Ground Fault
Cooling Method	Liquid Cooled
Storage Temperature	-25°C to +70°C
Relative Humidity	5-95% non-condensing
Altitude	Up to 1000m (3280ft) without derating, up to 4000m (13120ft) with derating
Operating Temperature	-10°C to +50°C (14°F to 122°F)