Danfoss VLT Refrigeration Drive FC 103 Design Manual page 50

System Integration
Leakage current
3 3
Illustration 3.6 Motor cable length and power size influence
on leakage current. Power size a > power size b
The leakage current also depends on the line distortion.
Leakage current
Illustration 3.7 Line Distortion Influences Leakage Current
If the leakage current exceeds 3.5 mA, compliance with
EN/IEC61800-5-1 (power drive system product standard)
requires special care. Reinforce grounding with the
following protective ground connection requirements:
•
Ground wire (terminal 95) of at least 10 mm
cross-section.
•
2 separate ground wires both complying with the
dimensioning rules.
See EN/IEC61800-5-1 and EN 50178 for further information.
48
®
VLT Refrigeration Drive FC 103
Using RCDs
Where residual current devices (RCDs), also known as earth
leakage circuit breakers (ELCBs), are used, comply with the
following:
a
•
•
•
The leakage current includes several frequencies
b
originating from both the mains frequency and the
switching frequency. Whether the switching frequency is
Motor cable length
detected depends on the type of RCD used.
Leakage current
THDv=0%
Illustration 3.8 Main Contributions to Leakage Current
THDv=5%
The amount of leakage current detected by the RCD
depends on the cut-off frequency of the RCD.
2
Illustration 3.9 Influence of the RCD Cut-off Frequency on
Leakage Current
Danfoss A/S © 08/2015 All rights reserved.
Use RCDs of type B only as they can detect 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
RCD with high f
50 Hz 150 Hz
Mains 3rd harmonics
Leakage current [mA]
cut-
cut-
Frequency
f
sw
Cable
100 Hz
2 kHz
100 kHz
MG16G202