Galvanic Isolation (Pelv); Pelv - Protective Extra Low Voltage - Danfoss VLT Decentral Drive FCD 302 Design Manual

Product Overview
2.4.1 Earth Leakage Current
2 2 Follow national and local codes regarding protective
earthing of equipment with a leakage current >3.5 mA.
Frequency converter technology implies high frequency
switching at high power. This will generate a leakage
current in the earth connection. A fault current in the
frequency converter at the output power terminals might
contain a DC component which can charge the filter
capacitors and cause a transient earth current.
The earth leakage current is made up of several contri-
butions and depends on various system configurations
including RFI filtering, screened motor cables, and
frequency converter power.
Illustration 2.20 Influence of Cable Length and Power Size on
Leakage Current for Pa>Pb
The leakage current also depends on the line distortion
Illustration 2.21 Influence of Line Distortion on Leakage Current
NOTE
When a filter is used, turn off 14-50 RFI Filter when
charging the filter, to avoid that a high leakage current
makes the RCD switch.
EN/IEC61800-5-1 (Power Drive System Product Standard)
requires special care if the leakage current exceeds 3.5 mA.
Earth grounding must be reinforced in one of the
following ways:
24
Leakage current [mA]
a
b
Cable length [m]
Leakage current [mA]
THVD=0%
THVD=5%
MG04H102 - VLT
®
VLT Decentral Drive FCD 302
•
•
See EN/IEC61800-5-1 and EN50178 for further information.
Using RCDs
Where residual current devices (RCDs), also known as earth
leakage circuit breakers (ELCBs), are used, comply with the
following:
•
•
•
Illustration 2.22 Main Contributions to Leakage Current
Illustration 2.23 Influence of Cut-off Frequency of the RCD
See also RCD Application Note, MN90G.

2.5 Galvanic Isolation (PELV)

2.5.1 PELV - Protective Extra Low Voltage

PELV offers protection by way of extra low voltage.
Protection against electric shock is ensured when the
electrical supply is of the PELV type and the installation is
made as described in local/national regulations on PELV
supplies.
®
is a registered Danfoss trademark
Earth ground wire (terminal 95) of at least 10
2
mm
Two separate earth ground wires both complying
with the dimensioning rules
Use RCDs of type B only which are capable of
detecting AC and DC currents
Use RCDs with an inrush delay to prevent faults
due to transient earth currents
Dimension RCDs according to the system configu-
ration and environmental considerations
RCD with low f
L [mA]
leakage
RCD with high f
50 Hz 150 Hz f
sw
Mains 3rd harmonics
Cable
f
s
Leakage current [mA]
100 Hz
2 kHz
100 kHz
cut-off
cut-off
f [Hz]