Danfoss VLT 2800 Series, Operating Instructions Manual

Page: 84 / 103

Derating for high switching frequency - VLT 2800
A higher switching frequency (to be set in parameter
411,
Switching frequency ) leads to higher losses in the
electronics of the frequency converter.
VLT 2800 has a pulse pattern in which it is possible to
set the switching frequency from 3.0- 10.0/14.0 kHz.
The frequency converter will automatically derate the
rated output current I
VLT,N,
when the switching frequen-
cy exceeds 4.5 kHz.
In both cases, the reduction is carried out linearly,
down to 60% of I
VLT,N
.
Temperature-dependent switch frequency
This function ensures the highest possible switch fre-
quency without the frequency converter becoming
thermally overloaded. The internal temperature is the
actual expression of the degree to which the switch
frequency can be based on the load, the ambient tem-
perature, the supply voltage and the cable length.
The function ensures that the frequency converter au-
tomatically adjusts the switch frequency between f
sw,
min
and f
sw, max
(parameter 411), see drawing below.
When using the LC filter the minimum switch frequen-
cy is 4.5 kHz.
Galvanic Isolation (PELV)
PELV (Protective Extra Low Voltage) insulation is ach-
ieved by inserting galvanic isolators between the con-
trol circuits and circuits that are connected to the mains
potential. The VLT is designed to meet the require-
ments for protective separation by means of having the
necessary creepage and clearance distances. These
requirements are described in standard EN 50 178. It
is also a requirement that the installation is carried out
as described in local/national regulations regarding
PELV.
The Protective Extra Low Voltage (PELV) require-
ments stated in IEC 61800-5-1 are not fulfilled at alti-
tudes above 2000 m (6562 ft.). For 200V frequency
converters the requirements are not fulfilled at alti-
tudes above 5000 m (16 404 ft.). Please contact Dan-
foss Drives for further information.
All control terminals, terminals for serial communica-
tion and relay terminals are safely separated from the
mains potential, i.e. they comply with the PELV re-
quirements. Circuits that are connected to control ter-
minals 12, 18, 19, 20, 27, 29, 33, 42, 46, 50, 53, 55
and 60 are galvanically connected to one another. Se-
rial communication connected to fieldbus is galvani-
cally insulated from the control terminals, although this
is only a functional insulation.
The relay contacts on terminals 1 - 3 are insulated from
the other control circuits with reinforced/double isola-
tion, i.e. PELV is observed for these, even though
there is mains potential at the relay terminals.
The circuit elements described below form the safe
electric separation. They fulfill the requirements for re-
VLT
®
2800 Series
MG.27.A2.02 - VLT
®
is a registered Danfoss trademark 83
All a
bou
t
VLT 2
800