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Galvanic Isolation (PELV)
PELV offers protection by way of extra low voltage.
Protection against electric shock is considered to be
ensured when the electrical supply is of the PELV type
and the installation is made as described in local/na-
tional regulations on PELV supplies.
All control terminals and relay terminals 01-03 comply
with PELV (Protective Extra Low Voltage) (Does not
apply to 525-600 V units).
Galvanic (ensured) isolation is obtained by fulfilling re-
quirements concerning higher isolation and by provid-
ing the relevant creapage/clearance distances. These
requirements are described in the EN 50178 standard.
The components that make up the electrical isolation,
as described below, also comply with the requirements
concerning higher isolation and the relevant test as
described in EN 50178.
The galvanic isolation can be shown in five locations
(see drawing below), namely:
1.
Power supply (SMPS) incl. signal isolation of
U
DC
, indicating the intermediate current volt-
age.
2.
Gate drive that runs the IGBTs (trigger trans-
formers/opto-couplers).
3.
Current transducers (Hall effect current
transducers).
4.
Opto-coupler, brake module.
5.
Opto-coupler, 24 V external supply.
Galvanic isolation
Earth leakage current
Earth leakage current is primarily caused by the ca-
pacitance between motor phases and the motor cable
screen. When an RFI filter is used, this contributes ad-
ditional leakage current, as the filter circuit is connec-
ted to earth through capacitors.
The size of the leakage current to the ground depends
on the following factors, in order of priority:
1.
Length of motor cable
2.
Motor cable with or without screen
3.
Switching frequency
4.
RFI filter used or not
5.
Motor grounded on site or not
The leakage current is of importance to safety during
handling/operation of the adjustable frequency drive if
(by mistake) the adjustable frequency drive has not
been earthed.
NOTE
Since the leakage current is >3.5 mA, re-
inforced earthing must be established,
which is required if EN 50178 is to be
complied with. For 3-phased adjustable
frequency drives, only fault current relays
which are suitable for protection against
DC currents (Din VDE 0664) are to be
used. RCD fault current relays type B
comply with these requirements accord-
ing to the norm IEC 755-2.
VLT
®
5000 Series
MG.51.C5.22 - VLT
p
is a registered Danfoss trademark.
207
List of functions
Summary of Contents for VLT 5000 Series
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