Danfoss VLT AQUA Drive FC 202 Design Manual page 55

System Integration
The ground leakage current is made up of several contri-
butions and depends on various system configurations,
including:
•
RFI filtering
•
Motor cable length
•
Motor cable shielding
•
Adjustable frequency drive power
Leakage current
Figure 3.6 Motor Cable Length and Power Size Influence on
Leakage Current. Powersize a > Powersize b
The leakage current also depends on the line distortion.
Leakage current
Figure 3.7 Line Distortion Influences Leakage Current
MG20N622
Design Guide
Compliance with EN/IEC61800-5-1 (power drive system
product standard) requires special care if the leakage
current exceeds 3.5 mA. Reinforce grounding with the
following protective ground connection requirements:
•
•
See EN/IEC61800-5-1 and EN50178 for further information.
a
Using RCDs
Where residual current devices (RCDs), also known as
ground leakage circuit breakers (GLCBs), are used, comply
with the following:
•
•
b
•
Motor cable length
The leakage current includes several frequencies
originating from both the line power frequency and the
switching frequency. Whether the switching frequency is
detected depends on the type of RCD used.
Leakage current
THVD=0%
THVD=5%
Figure 3.8 Main Contributions to Leakage Current
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Ground wire (terminal 95) of at least 10 mm
AWG) cross-section.
Two separate ground wires both complying with
the dimensioning rules
Use RCDs of type B only as they are capable of
detecting AC and DC currents.
Use RCDs with a delay to prevent faults due to
transient ground currents.
Dimension RCDs according to the system configu-
ration and environmental considerations.
RCD with low f
cut-
RCD with high f
50 Hz 150 Hz
Mains 3rd harmonics
2
(7
cut-
Frequency
f
sw
Cable
53
3 3